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Population size estimation of breeding Red-faced and Grace’s Warblers in pine woodlands of New Mexico: 2015 Report

Prepared for: Share with Wildlife Program

New Mexico Department of Game and Fish 1 Wildlife Way

Santa Fe, NM 87507

Prepared by: Envirological Services, Inc.

www.enviroinc.org

January 29, 2016

Table of Contents

Introduction............................................................................................................................... 3

Methods ..................................................................................................................................... 5 Site Selection ................................................................................................................... 5 Survey Methodology ....................................................................................................... 5 Analysis .......................................................................................................................... 5

Results ....................................................................................................................................... 7 Suitable Habitat ............................................................................................................... 7 Target Species Density and Population Estimate .............................................................. 7 Species Diversity and Abundance .................................................................................... 8 Species of Greatest Conservation Need ….. ................................................................... 10

Discussion ................................................................................................................................ 11 Habitat and Microhabitat ............................................................................................... 11 Evaluation of Suitable Habitat ....................................................................................... 11 Presence and Density of Target Species ......................................................................... 13 Study Limitations .......................................................................................................... 14 Population Trends and Estimates ................................................................................... 14 Future Work .................................................................................................................. 15

Acknowledgements .................................................................................................................. 16

Literature Cited ...................................................................................................................... 17

List of Tables Table 1. Total size of survey areas, and extent and breakdown of suitable habitat within these

areas ............................................................................................................................. 7 Table 2. Detection probability (p̂ ), density (D), total suitable habitat, and population estimates

with upper and lower limits for Grace’s (GRWA) and Red-faced Warblers (RFWA) in the six mountain ranges surveyed in New Mexico ......................................................... 8

Table 3. Number and location of Species of Greatest Conservation Need recorded during 2015 surveys ....................................................................................................................... 10

List of Maps Map 1. Overview of Grace’s and Red-faced Warbler survey route locations in the Zuni, San

Mateo, and Magdalena Mountains in New Mexico. ...................................................... 19 Map 2. Overview of Grace’s and Red-faced Warbler survey route locations in the Jemez, Sandia,

and Manzano Mountains of New Mexico. .................................................................... 20

Population size estimation of breeding Red-faced and Grace’s Warblers in pine woodlands of NM, 2015

Envirological Services, Inc. www.enviroinc.org

Map 3. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Sandia Mountains, Sandia Ranger District, Cibola National Forest, New Mexico. .................................................................................................... 21

Map 4. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Manzano Mountains, Mountainair Ranger District, Cibola National Forest, New Mexico. ...................................................................................... 22

Map 5. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Zuni Mountains, Mt. Taylor Ranger District, Cibola National Forest, New Mexico. .................................................................................................... 23

Map 6. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Magdalena Mountains, Magdalena Ranger District, Cibola National Forest, New Mexico. ...................................................................................... 24

Map 7. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the San Mateo Mountains, Magdalena Ranger District, Cibola National Forest, New Mexico. ...................................................................................... 25

Map 8. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Jemez Mountains, Jemez Ranger District, Santa Fe National Forest, New Mexico. .................................................................................................... 26

List of Appendices Appendix A. Species detected during surveys, listed in taxonomic order, and their NMDGF

conservation status .............................................................................................. 27 Appendix B. Species relative abundance by site, and total abundance and diversity measures for

each site including total number of individuals recorded, total abundance, Shannon’s index, evenness, and species richness ................................................. 30

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Introduction

The Red-faced Warbler (Cardellina rubrifrons) and the Grace’s Warbler (Setophaga graciae) are New Mexico Department of Game and Fish (NMDGF) Species of Greatest Conservation Need (NMDGF 2015), and they are current priority nongame bird species. However, much of the information necessary for effective conservation and management is lacking. Population estimates are limited for Grace’s Warblers and unavailable for Red-faced Warblers. Information about breeding biology for these two species is also limited, and for the Red-faced Warbler, no specific information exists for New Mexico (Martin and Barber 1995, Stacier and Guzy 2002). Nevertheless, both warbler species face high risk as they breed in pine habitats that have experienced loss and degradation over time. This project was conducted to establish baseline population size estimates of breeding Red-faced and Grace’s Warblers in six mountain ranges of New Mexico, to allow for identification and documentation of status and trends, and aid NMDGF with management decisions.

The breeding distributions for both the Red-faced and Grace’s Warbler are primarily limited to New Mexico, Arizona, and the Sierra Madre Occidental mountains of Mexico; thus New Mexico serves an important role and has a high stewardship responsibility for these species with limited ranges. The ranges of these two species overlap in parts of New Mexico including in the San Mateo, Magdalena, Sacramento, and Gila mountain ranges. Grace’s Warblers are additionally present in most mountain ranges of central and northern New Mexico. Both species occupy pine-oak woodlands at elevations from 1,800 – 2,800 m. Red-faced Warblers additionally utilize habitats including Douglas fir, spruce, or aspen trees while the Grace’s Warbler is considered a pine specialist, most commonly occurring in ponderosa pine (Pinus ponderosa) woodlands in New Mexico.

Size of the New Mexico population for both of these species is unknown (NMPIF 2007). Grace’s Warblers are more common, with a larger range, and are encountered more frequently on surveys such as the North American Breeding Bird Survey (BBS) than Red-faced Warblers (Sauer et al. 2014). Red-faced Warblers are detected on very few BBS routes, and their low detection rates prevent population size estimates using this method. Both Red-faced and Grace’s Warbler are listed as a national and Southwest Region Bird of Conservation Concern by the United States Fish and Wildlife Service (USFWS 2008). New Mexico Partners in Flight ranks both species as high priority with high vulnerability as Level 1 Species of Conservation Concern, with Grace’s Warblers’ vulnerability due to sharp population declines in New Mexico and Red-faced Warblers’ ranking stemming from small distribution and small population size (NMPIF 2007). It is suggested these species are relatively intolerant of disturbance and habitat degradation (Martin and Barber 1995, Stacier and Guzy 2002). Potential factors influencing Red-faced and Grace’s Warbler populations in New Mexico include habitat loss and alteration due to timber harvest and grazing, as well as recent loss from fire and current risk of catastrophic fire (NMDGF 2015). Therefore, it is important to establish baseline information on population sizes in order to understand how these species are affected by potentially harmful activities.

In order to document population sizes over the vast state of New Mexico, surveys were spread geographically over multiple years. Surveys in 2015 were conducted in the Sandia, Manzano, Magdalena, San Mateo, Zuni, and Jemez mountain ranges. Future surveys will take place during the 2016 breeding season in the San Juan, Jemez, Sangre de Cristo, and Sacramento mountain ranges. A third year of surveys will be proposed for the Gila mountain region of




southwestern New Mexico. Together, these surveys will build towards estimating statewide population sizes for these two species.

Methods

Site Selection

The 2015 surveys were conducted in six mountain ranges in central New Mexico (Maps 1 – 2). These survey sites included: the Sandia (Map 3), Manzano (Map 4), Zuni (Map 5),Magdalena (Map 6), and San Mateo (Map 7) Mountains of the Cibola National Forest and the Jemez Mountains (Map 8) of the Santa Fe National Forest. All surveys were conducted on public lands and required no infrastructure or ground disturbance. Project areas of suitable habitat for breeding Red-faced and Grace’s Warblers were identified using range maps, habitat maps, GIS layers, published literature, BBS sightings, eBird sightings, and general knowledge. Survey sites were selected in areas where approximately 2 miles of surveyable habitat was present, where land-ownership was public, and in ponderosa pine habitats, especially with oak associations, along part of or the entire survey route. Survey routes were placed most frequently along drainage bottoms, but also on trails or lightly used roads. Survey routes were conducted at elevations between 2,064 – 2,779 m (6,771 – 9,117 ft). Four survey routes were selected in each mountain range, and were surveyed twice. In the San Mateo Mountains, five routes were selected in order to avoid a fire closure area during the second round of surveys. A total of 25 survey routes were sampled.

Survey Methodology

Point count surveys were conducted between May 1 and June 30 and followed survey guidelines outlined in Ralph et al. (1993, 1995). Two surveys were conducted at each survey route, and the two sampling periods at each site were spaced at least 10 days apart. Surveys were not conducted during periods of inclement weather, including periods with winds > 10 mph or periods of prolonged rain. Surveys began at sunrise and concluded at 10 AM. Survey routes varied in length according to access, terrain, and habitat, but were approximately 2 miles long and typically contained 16-18 points. Point count locations were recorded using GPS receivers (UTM zone 13 in meters, NAD 1983 datum). Points were spaced 200 m apart along each transect, and all avian species either seen or heard within a 100 m radius from each point were recorded; detections outside this radius were excluded. Each point was surveyed for 10 minutes, and the 10 minute duration was divided into three time periods in order to determine detection probability: 0-3 minutes, 3-5 minutes, and 5-10 minutes (Farnsworth et al. 2002). Birds were recorded separately during each time period, and for auditory or visual detections. Location information was also recorded for all other Species of Greatest Conservation Need detected during surveys. A habitat description at each point location was also recorded.

Analysis

Detection probability (p̂ ) for Grace’s and Red-faced Warblers was determined according to time removal model methods described in Farnsworth et al. (2002) and was calculated using




Program SURVIV (White 1992) and R (R Core Team 2013). Density was calculated using p̂ and total survey area. Detection probabilities and densities were calculated separately for each mountain range, and were made only for singing birds; visual detections were not included in analyses. Differences between detection probabilities between survey bouts were tested using student’s two-sample t-tests. Population estimates were extrapolated from the calculated density of each target species within a mountain range and the total estimated suitable habitat within that range. Because density was calculated from singing males only, density was doubled for the population estimate to reflect the assumption that the males were paired.

Suitable habitat was estimated within each mountain range using the best available, large-scale habitat information for the area. GIS layers were acquired from the U.S. Forest Service, Santa Fe (http://www.fs.usda.gov/detail/r3/landmanagement/gis/?cid=stelprdb5203736) and Cibola (http://www.fs.usda.gov/detail/r3/landmanagement/gis/?cid=stelprdb5212078) National Forests. We used mid-scale existing vegetation dominance type, canopy cover, and elevation data. Remote sensing data (NLCD) available from the U.S. Geological Survey was also considered, but NLCD data only defines either evergreen, deciduous, or mixed forest types, and vegetation type is not further defined from these broad categories. Forest Service GIS layers provided the best resolution for smaller-scale habitat features. Because we estimated p̂ separately for each mountain range we also estimated total suitable habitat separately for each range. We estimated total suitable habitat for each ranger district or for each separate unit when ranger districts were made up of distinct units. For example, the Mount Taylor Ranger District on the Cibola National Forest contains two discrete units, one encompassing the Zuni Mountains where our surveys were conducted, and the other unit encompassing Mount Taylor and the surrounding area where no surveys were conducted.

To estimate total suitable habitat for each range, we included mid-scale existing vegetation dominance types defined in the Cibola National Forest as: ponderosa pine mix; ponderosa pine-Douglas fir (Pseudotsuga menziesii) mix; Douglas fir, white fir (Abies concolor), and deciduous-evergreen tree mix; and in the Santa Fe National Forest as: ponderosa pine mix; upper deciduous-evergreen forest tree mix; and spruce-fir (Picea, Abies). Because the two warbler species occupy mature ponderosa habitat, we only included suitable habitat types with greater than 30% canopy cover. Finally, because Grace’s Warblers breed between 1,800 – 2,700 m (Stacier and Guzy 2002), and Red-faced Warbler breed between 2,000 – 2,800 m (Martin and Barber 1995), we also excluded any habitat above 2,820 m. All mapping analysis was completed using ESRI ArcMap 10.1.

To examine abundance and diversity of all recorded species, point count data was analyzed by calculating species richness (total number of species detected), Shannon’s index (H = -∑ [(pi)(lnpi)]), evenness (E = H/lnS), total number of individuals, and total abundance of all species combined. Relative abundance (pi = ni/N) was calculated to describe the proportion of total individuals comprised of any single species, and was used to describe species relatively common or rare within the study area. Differences in abundance and diversity between study sites were tested using one-way ANOVA. Statistical analyses were performed in R version 3.0.1 (R Core Team 2013) and were evaluated at an α-level of 0.05.


http://www.fs.usda.gov/detail/r3/landmanagement/gis/?cid=stelprdb5203736

http://www.fs.usda.gov/detail/r3/landmanagement/gis/?cid=stelprdb5212078



Results

Suitable Habitat

We estimated that 223,700 ha of suitable habitat are present in the six mountain ranges that we surveyed (Table 1).

Table 1. Total size of survey areas, and extent and breakdown of suitable habitat within these areas. All survey areas lie within the Cibola National Forest except the Jemez Ranger District that lies in the Santa Fe National Forest. All sizes are reported in hectares. Survey area (mountain

range)

Total size Suitable habitat

Ponderosa pine mix

Ponderosa pine - Douglas

fir mix

Douglas fir, white fir or spruce-fir

Deciduous -evergreen tree mix

Jemez 99,375 52,956 37,239 * 218 15,499 Magdalena 39,865 10,472 3,631 2,767 944 3,130 Manzano 48,788 21,091 14,009 2,129 2,327 2,625

Sandia 49,192 13,040 6,787 732 2,791 2,730 San Mateo 165,033 30,691 13,280 10,121 3,146 4,143

Zuni 175,818 95,450 79,918 6,225 981 8,325 * Each forest uses slightly different habitat designations in their GIS mapping products. Ponderosa pine-Douglas firmix designation is not used on Santa Fe National Forest.

Target Species Density and Population Estimate

Grace’s Warblers were detected in all of the sampled mountain ranges and were detected along every survey route. Red-faced Warblers were detected only in the Magdalena and San Mateo mountain ranges. In the Magdalena and San Mateo ranges, Red-faced Warblers were detected along every survey route. Both warbler species were detected along the entire range of elevations surveyed.

Detection probability (p̂ ) did not vary between survey bouts for Grace’s Warblers (t = 0.4491, df = 7.841, P = 0.6655) or for Red-faced Warblers (t = -1.7589, df = 2.201, P = 0.2091). Therefore we used the combined detection probability from both survey bouts to estimate density for both species. Detection probabilities were estimated separately for each mountain range.

Density of target species varied between mountain ranges (Table 2). The highest Grace’s Warbler density was recorded in the Manzano Mountains (0.93 ± 0.09 singing birds ha-1) and the lowest density was recorded in the San Mateo Mountains (0.28 ± 0.11 singing birds ha-1). Red-faced Warbler density was higher in the San Mateo Mountains (0.42 ± 0.07 singing birds ha-1) than in the Magdalena Mountains (0.22 ± 0.04 singing birds ha-1). Within the six mountain ranges that we surveyed, we estimate the population size of Grace’s Warblers to be between 201,094 and 358,615 individuals, and Red-faced Warblers to be between 19,950 and 40,598 individuals.




Table 2. Detection probability (p̂ ), density (D), total suitable habitat, and population estimates with upper and lower limits based on 95% confidence intervals for Grace’s (GRWA) and Red-faced Warblers (RFWA) in the six mountain ranges surveyed in New Mexico. Densities were estimated for singing males, therefore total population estimates reflect 2(D)*suitable habitat (see Table 1 for habitat estimates).

Range Species p̂ ± SE D (SE) (singing

birds ha-1)

Total suitable

habitat (ha)

Population estimate

Population estimate (95% CI)

Jemez GRWA 0.75 ± 0.10 0.76 (0.11) 52,956 80,515 58,115 – 102,914 Magdalena GRWA 0.75 ± 0.14 0.39 (0.07) 10,472 8,070 5,030 – 11,110 Manzano GRWA 0.76 ± 0.07 0.93 (0.09) 21,091 39,127 31,331 – 46,924

San Mateo GRWA 0.64 ± 0.25 0.28 (0.11) 30,691 17,384 3,608 – 31,162 Sandia GRWA 0.77 ± 0.09 0.79 (0.09) 13,040 20,504 15,747 – 25,261 Zuni GRWA 0.78 ± 0.09 0.60 (0.07) 95,450 114,253 87,263 – 141,243 Total GRWA 279,854 201,094 – 358,615 Jemez RFWA - 0 52,956 - -

Magdalena RFWA 0.81 ± 0.12 0.22 (0.04) 10,472 4,678 3,182 – 6,174 Manzano RFWA - 0 21,091 - -

San Mateo RFWA 0.75 ± 0.12 0.42 (0.07) 30,691 25,596 16,768 – 34,424 Sandia RFWA - 0 13,040 - - Zuni RFWA - 0 95,450 - - Total 30,274 19,950 – 40,598

Species Diversity and Abundance

Eighty-three species were recorded during surveys (Appendix A). Species richness was highest in the Magdalena Mountains (n = 56 species) and was lowest in the Zuni Mountains (n = 44 species). Examining diversity metrics, there was no significant difference in species richness (F5,18 = 1.823, P = 0.159), Shannon’s index (F5,18 = 2.131, P = 0.108), or evenness (F5,18 = 1.082, P = 0.404) among the six mountain ranges.

Including all bird species, 9,080 bird records were obtained during the surveys (Appendix B). Avian abundance was highest in the Sandia Mountains (4.3 birds ha-1) and lowest in the Magdalena Mountains (3.1 birds ha-1). Examining measures of abundance, there was no significant difference in the total number of individuals (F5,18 = 2.000, P = 0.127) or total abundance (F5,18 = 1.527, P = 0.231) among the six mountain ranges.

In the Jemez Mountains, the Grace's Warbler, American Robin, and Hermit Thrush were the most abundant birds. Approximately half (52%) of the total individuals were comprised of Grace's Warbler, American Robin, Hermit Thrush, Mountain Chickadee, Ruby-crowned Kinglet, Western Tanager, Pine Siskin, Turkey Vulture, Yellow-rumped Warbler, and Cordilleran Flycatcher.

In the Manzano Mountains, the American Robin, Grace's Warbler, and Mountain Chickadee were the most abundant birds. 53% of the total individuals were comprised of American Robin, Grace's Warbler, Mountain Chickadee, Hermit Thrush, Western Tanager, Spotted Towhee, and Dark-eyed Junco.

In the Magdalena Mountains, the Western Tanager, Plumbeous Vireo, and Mountain Chickadee were the most abundant birds. 53% of the total individuals were comprised of




Western Tanager, Plumbeous Vireo, Mountain Chickadee, Spotted Towhee, Grace's Warbler, Cordilleran Flycatcher, Hermit Thrush, Black-headed Grosbeak, and Broad-tailed Hummingbird.

In the Sandia Mountains, the Mountain Chickadee, Broad-tailed Hummingbird, and Grace's Warbler were the most abundant birds. 50% of the total individuals were comprised of Mountain Chickadee, Broad-tailed Hummingbird, Grace's Warbler, Black-headed Grosbeak, Plumbeous Vireo, Western Tanager, and Pine Siskin.

In the San Mateo Mountains, the Pine Siskin, Mountain Chickadee, and Steller's Jay were the most abundant birds. 50% of the total individuals were comprised of Pine Siskin, Mountain Chickadee, Steller's Jay, American Robin, Dark-eyed Junco, Red-faced Warbler, and Hermit Thrush.

In the Zuni Mountains, the Mountain Chickadee, Black-headed Grosbeak, and Pine Siskin were the most abundant birds. 53% of the total individuals were comprised of Mountain Chickadee, Black-headed Grosbeak, Pine Siskin, Grace's Warbler, Steller's Jay, Western Tanager, and Common Raven.




Species of Greatest Conservation Need

Twenty-two Species of Greatest Conservation Need were recorded during surveys (Table 3, Appendix A). The number of species was highest in the San Mateo Mountains (n = 12 species) and was lowest in the Sandia Mountains (n = 8 species).

Table 3. Number and location of Species of Greatest Conservation Need recorded during 2015 surveys.

Common Name Number of individuals

Jemez Manzano Magdalena Sandia San Mateo Zuni Montezuma Quail 5 Northern Goshawk 2 Band-tailed Pigeon 2 1 6 11 Mourning Dove 4 14 10 24 1 1 Flammulated Owl 1 1 1 Mexican Spotted Owl 3 Williamson's Sapsucker 2 Peregrine Falcon 1 Olive-sided Flycatcher 1 2 2 1 Pinyon Jay 2 8 65 Clark's Nutcracker 38 4 6 Juniper Titmouse 2 Pygmy Nuthatch 55 6 10 53 38 Western Bluebird 36 7 19 15 Virginia's Warbler 6 3 11 16 5 Grace's Warbler 118 167 68 118 45 91 Black-throated Gray Warbler 4 7 5 Red-faced Warbler 42 80 Painted Redstart 7 Black-chinned Sparrow 4 Cassin's Finch 1 Evening Grosbeak 1

Total individuals of all SGCN 227 235 160 184 224 229 Total abundance of all SGCN

combined (individuals/ha) 0.547 0.502 0.374 0.465 0.509 0.583 SGCN species richness 9 10 10 8 12 9




Discussion

Habitat and Microhabitat

Grace’s Warblers and Red-faced Warblers use largely similar habitats, occupying mature ponderosa pine forests in New Mexico. However, they specialize in ponderosa habitats to different degrees and vary in their specific habitat preferences. These differences should be considered when examining the results of this study. Grace’s Warblers are characteristic of ponderosa habitats, and are 2-3 times more abundant in ponderosa habitats than in comparison areas (Carothers et al. 1973, in Block and Finch 1997). They rely heavily on pines for foraging activities (Szaro and Balda 1979). Grace’s Warblers are found in forests with relatively high canopy closure (the average canopy closure was 46% in an Arizona study), and they are especially associated with ponderosa pine woodlands with Gambel’s oak (Quercus gambelii) understories (Stacier and Guzy 2002). Grace’s Warblers are often found in dry, park-like habitats and may occupy mesa tops and lower canyon bottoms (Stacier and Guzy 2002).

Red-faced Warblers also utilize ponderosa habitats, but do not use these habitats as exclusively as Grace’s Warblers. Red-faced Warblers are associated with fir, spruce, Douglas fir, aspen (Populus), and maple (Acer) in addition to ponderosa pine. A ground-nesting species, Red-faced Warblers most frequently place nests at the bases of fir or maple trees and only rarely at the base of ponderosa pine, and they are commonly found in drainage bottoms (Martin and Barber 1995).

The two warbler species also show differences in their tolerance of disturbance and their elevational range. Although both species are relatively intolerant of disturbance and habitat degradation (Martin and Barber 1995, Stacier and Guzy 2002), Red-faced Warblers use mature ponderosa forests in undisturbed or lightly disturbed areas, while Grace’s Warblers use lightly to moderately disturbed ponderosa habitats (Szaro and Balda 1982). There is a large degree of overlap in the elevational ranges that these two species occupy, though Red-faced Warblers occupy a slightly higher range of elevations. However, both species occupied the entire range of elevations that we surveyed, so we believe their presence is not defined solely by elevation.

Evaluation of Suitable Habitat

We estimated the extent of mature ponderosa pine and other appropriate habitat types for these two species using GIS map layers. These layers approximate the dominant vegetation type and the canopy cover for the areas that we surveyed. However, as discussed above, these two species utilize different microhabitats that cannot be described by large-scale GIS layers. The basic habitat types used by these two species (ponderosa pine, Douglas fir, fir, spruce, and deciduous tree species) are similar, but each species shows a preference to, but not exclusion of, certain habitat types (i.e. Grace’s Warblers in ponderosa, Red-faced Warbler association with fir and maple). For this reason, estimates of suitable habitat based on broad scale information will likely overestimate actual suitable habitat for both species. In order to more specifically determine total suitable habitat for these species, a large-scale vegetation survey would need to occur. To ground-truth GIS layers and differentiate smaller scale habitat features would be a very large undertaking, and was beyond the scope of this project.

This study did not take into account certain habitat features that could impact habitat suitability, such as location on a slope, steepness of a slope, recent wildfire activity, or tree




density. Often, survey routes were located at the bottom of drainages, with some point count locations mid-slope and a few points along ridges or mesa tops. The drainages varied in steepness from broad, park-like forests with shallow slopes to more incised, narrow drainages with steep slopes. It is not known whether density of our target species varied according to location on a slope or steepness, and these two factors could be confounding. Location on a slope may play a role in determining presence for Red-faced Warblers, who may preferentially use steeper-walled canyon bottoms, where mesic tree species such as maple or fir are more likely to occur (Martin and Barber 1995). Grace’s Warblers may use more park-like habitats or mesa tops, both of which are relatively flat habitats, and these habitats may occur both in drainage bottoms and on the uppermost slopes. There is no quantitative information that defines habitat use by location on a slope or steepness for these species. The presence or density of Grace’s and Red-faced Warblers may be defined more by the microhabitat conditions that are created by steepness or location on a slope than by these factors intrinsically. Future studies may aim to determine whether density of Grace’s and Red-faced Warblers are similar along drainage bottoms, mid-slope, and upper slopes, and whether steepness plays a differential role in defining occurrence or density.

Recent wildfires could also affect the availability of suitable habitat for these two species. Historically, wildfire has played an important ecological role in southwestern ponderosa pine forests. Frequent, low-intensity fires burned every 2-47 years (Fitzgerald 2005), clearing ground fuels, saplings, and shrub layers, but leaving mature trees intact. After decades of fire suppression, fuels accumulated, and present-day fires now burn at greater sizes and intensities and often result in catastrophic stand-replacing fires (Fitzgerald 2005). The impact of fires on these two warbler species is not clear, and should vary based on fire intensity. Two Arizona studies showed conflicting results: in one study, Grace’s Warblers were more abundant in non-burned areas (Overturf 1979, in Block and Finch 1997), and in another study, they were more abundant in burned areas (Blake 1982, in Block and Finch 1997); fire intensity was not discussed.

The occurrence of wildfire in ponderosa pine forests in New Mexico does not necessarily result in loss of suitable habitat, but severe fires that destroy ground cover and small trees as well as mature trees will result in habitat loss. In calculating total suitable habitat for this study, we attempted to eliminate some habitat that had recently burned, but found the available GIS layers inadequate at describing whether suitable habitat had actually been lost. For example, in 2014, the Pino fire on the Jemez Ranger District burned approximately 4,300 acres. The boundary of this fire lies along one of our survey routes in Paliza Canyon (Map 8), which was a route where we observed mature ponderosa pine and detected Grace’s Warbler at nearly every point. However, the 2004 Trigo fire that burned 14,000 acres in the Manzano Mountains was a severe, stand-replacing fire within much of the burn area. This burn scar is mostly devoid of mature live trees and does not provide suitable ponderosa pine habitat for these species. However, in available GIS layers, only the boundaries and not the severity of fires are displayed, and this information does not accurately describe whether the habitat within fire boundaries is suitable for these species. Therefore we did not attempt to exclude suitable habitat from areas recently impacted by wildfire, though severe wildfire will certainly limit available habitat for these species.




Presence and Density of Target Species

The variation in density of Grace’s and Red-faced Warblers across the mountain ranges we surveyed may reflect the distributional limits of these two species, the availability of suitable microhabitat, and the quality of habitat. Grace’s Warblers were detected on every survey route, although they occurred in varying densities. Density ranged from 0.28 ± 0.11 singing birds ha-1

in the San Mateo Mountains to 0.93 ± 0.09 singing birds ha-1 in the Manzano Mountains (Table 2). Grace’s Warbler density was considerably lower in the Magdalena and San Mateo mountains than in the other four ranges (Table 2). Interestingly, these two ranges were also the only ranges where Red-faced Warblers were detected. Red-faced Warbler densities were similar in the Magdalena (0.22 ± 0.04 singing birds ha-1) and San Mateo (0.42 ± 0.07 singing birds ha-1) mountains, though somewhat greater in the San Mateo Mountains. The combined density of Grace’s and Red-faced Warblers was 0.61 singing birds ha-1 in the Magdalena Mountains and 0.70 singing birds ha-1 in the San Mateo Mountains; densities much more similar to those recorded for Grace’s Warblers alone in the four other mountain ranges.

Though these species co-occur in pine-oak woodlands, they differ in microhabitat preferences, breeding sites, and foraging behaviors. These differences are likely to alleviate direct competition for resources, but the similarities in habitat use for these two species could potentially be a limiting factor in ranges where both species occur, and could in part explain lower Grace’s Warbler densities in ranges where Grace’s and Red-faced Warblers co-occur. Alternatively, the neighboring Magdalena and San Mateo mountains are the southernmost ranges that we surveyed in 2015. On average, these ranges are drier and hotter than the other ranges we surveyed, with some of the cooler, more mesic habitats occurring above the elevational limit of the two target species. The drier nature of these ranges could also limit total bird density. We did not evaluate the density of all species on these ranges, but we found no significant difference in total abundance and diversity between the six mountain ranges that we surveyed, and the Magdalena Mountains had the highest species diversity.

We detected Red-faced Warblers in areas where they were previously known to breed (Magdalena and San Mateo mountains), but did not detect this species in the Zuni Mountains, which is included in the northern extent of the species breeding range (NMPIF 2007). Only one eBird sighting in this mountain range is documented (McCallum 1999), but birders have reported occasional sightings of this species in the Zuni Mountains. It is possible that we failed to detect this species in the Zuni Mountains due to a small sampling area. However, this species was easily detected in the ranges where it occurs, and while the Zuni Mountains may be a region of occasional sightings or even breeding, we do not expect that this range is the site of a significant breeding population. If present, they may be highly localized within suitable microhabitat.

According to eBird, Red-faced Warblers have also been detected in the Sandia Mountains, at the Rio Grande Nature Center (RGNC) in Albuquerque, and in Galisteo, NM (eBird 2012). These detections occurred in April and May and are likely representative of migrant or vagrant individuals. Two of these locations, the RGNC and Galisteo, do not offer suitable breeding habitat for this species. While the Sandia Mountains do have suitable breeding habitat, we did not detect Red-faced Warblers during these surveys, and we do not expect that sizable breeding populations occur in the Sandia Mountains.




Study Limitations

This study estimated the population of two forest-dwelling warblers based on density determined through survey data and estimation of suitable habitat. There are, of course, limitations associated with a study of this nature. First, there are assumptions inherent in establishing detection probabilities and therefore densities. These assumptions are fully discussed in Farnsworth et al. (2002), but in summary are: the population of birds within the detection radius does not change during the count interval, individuals are not double-counted, detection probability is constant throughout the count interval, and birds are correctly assigned to a distance category. Though these assumptions are likely to be violated to some degree, count-removal modeling is still one of the most robust methods available (Farnsworth et al. 2002).

We estimated detection probability and density for Grace’s and Red-faced Warblers within the areas that we surveyed. In extrapolating these estimates to large areas that were not surveyed, we make the assumptions that our survey areas are indicative of habitat as a whole within each mountain range, and the true density of these species is constant over the entire range of suitable habitat. We selected survey routes randomly, as long as they met certain criteria of general habitat type and overall length; therefore, routes should be representative of habitat within a mountain range. However, only four sampling sites per range may not truly capture the habitat characteristics or variability present within each mountain range.

We have attempted to conservatively estimate suitable habitat for these species using the best information available. However, limitations are also inherent in estimating total suitable habitat for a large area. As discussed above, large-scale GIS mapping is incapable of designating microhabitat features that may affect the presence or density of these two species, and may overestimate the suitable habitat, and therefore population sizes for these species.

Though there are limitations to making population estimates, this study provides baseline information about density and population size of Grace’s and Red-faced Warblers in New Mexico. We used the best available methods to cost-effectively cover a large portion of suitable habitat across many of the geographically disparate mountain ranges of New Mexico in a single breeding season. There is currently only limited information about the population size of these two species in New Mexico. This information is based on methods not specifically designed to estimate population size (discussed below). Here, we selected methodology targeted to making robust density estimates for forest dwelling species and provide current information about population sizes.

Population Trends and Estimates

Partners in Flight (PIF), using data from the North American Breeding Bird Surveys (BBS), estimate the population of Grace’s Warblers at around 414,825 individuals in New Mexico (Blancher et al. 2013). We estimated between 201,094 and 358,615 Grace’s Warblers in the six mountain ranges that we surveyed, and our estimates account for between 48% and 86% of the total population as estimated by PIF. However, we have surveyed only a small portion of the mountain ranges in New Mexico where this species is known to occur. Following future surveys, it is reasonable to assume that our estimate of the Grace’s Warbler population in New Mexico will exceed the estimate provided by PIF.

Partners in Flight estimate the population of Red-faced Warblers at around 106,399 individuals in New Mexico (Blancher et al. 2013). We estimated between 19,950 and 40,598




Red-faced Warblers in the mountain ranges that we surveyed, accounting for between 19% and 38% of the total population in New Mexico as estimated by PIF. The distribution of Red-faced Warblers in New Mexico is more confined than that of Grace’s Warblers, and the only remaining unsurveyed population centers for this species are the Sacramento and Gila mountains. However, these areas, and especially the Gila Mountains, are likely to house large numbers of Red-faced Warblers. It is unclear at this point how our population estimate for this species will compare to PIF population estimates.

Breeding Bird Surveys, which were used by PIF to make population estimates, were not designed to estimate population sizes, but rather to provide information on relative abundance and to evaluate trends in species abundance over time (Sauer et al. 2014). Neither of our target species receive “good” data quality ratings as described by BBS for New Mexico. Grace’s Warblers and Red-faced Warblers show high degrees of variance, and sample size for Red-faced Warblers on BBS routes is quite small. Indeed, not enough data is collected during BBS routes on Red-faced Warblers to estimate population trends, much less population size. The BBS trend for Grace’s Warbler shows a slight downward trend of 2.73% (between -0.43 and -5.17) per year between 1966 and 2013 in New Mexico (Sauer et al. 2014). BBS routes are placed along roads and only detect Grace’s Warblers on 18 of 66 routes, and Red-faced Warblers on 4 of 66 routes. Because these species inhabit mature forests, and prefer moderate degrees of disturbance at most, roadside habitats are unlikely to be representative of habitats most often used by these species. Grace’s Warblers were one of the most commonly detected species during our surveys in each mountain range, and Red-faced Warblers were fairly common where they occurred. Thus, due to the nature of BBS routes, populations of these forest-dwelling birds are unlikely to be accurately described via this method.

Our study provides a targeted approach to estimating the population of these two warbler species in New Mexico. These methods can easily be applied in the future to evaluate additional population centers for these birds, and to reevaluate the 2015 survey areas in order to determine changes in population size and trends. This information will be useful in making management decisions regarding these species and their preferred habitats.

Future Work

To expand on these 2015 results, Grace’s and Red-faced Warbler surveys will be conducted in 2016 in additional regions of New Mexico. Locations for 2016 surveys will include the San Juan, Jemez, Sangre de Cristo, and Sacramento mountain ranges. Standardized surveys will follow the same methodology established for the 2015 project. In addition, the Gila National Forest and surrounding areas are important for both of these species. Due to the large size and numerous reports of Red-faced and Grace’s Warblers in this region, a third year of surveys will be proposed to estimate population sizes for these species in the Gila mountain region of southwestern New Mexico for 2017. Together with the 2015 results, these future studies will build towards statewide population estimates for these two warbler species.




Acknowledgements

We thank the New Mexico Department of Game and Fish for funding this project through the Share with Wildlife Program. This project was also supported by US Fish and Wildlife Service State Wildlife Grant T-32-4 project 5. We specifically thank Peggy Darr and Ginny Seamster of the NMDGF for their support and interest. Surveys were conducted by Ken Babcock, Corrie Borgman, Octavio Cruz-Carretero, and Kirsten Cruz-McDonnell of Envirological Services, Inc. Corrie Borgman performed the detection probability, density, and habitat analysis, created final map products, and prepared this report. Kirsten Cruz-McDonnell performed all other analyses and prepared this report.




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Map 1. Overview of Grace’s and Red-faced Warbler survey route locations in the Zuni, San Mateo, and Magdalena Mountains in New Mexico.




Map 2. Overview of Grace’s and Red-faced Warbler survey route locations in the Jemez, Sandia, and Manzano Mountains of New Mexico.




Map 3. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Sandia Mountains, Sandia Ranger District, Cibola National Forest, New Mexico.




Map 4. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Manzano Mountains, Mountainair Ranger District, Cibola National Forest, New Mexico.


Map 5. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Zuni Mountains, Mt. Taylor Ranger District, Cibola National Forest, New Mexico.

Map 6. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Magdalena Mountains, Magdalena Ranger District, Cibola National Forest, New Mexico.



Map 7. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the San Mateo Mountains, Magdalena Ranger District, Cibola National Forest, New Mexico.




Map 8. Location and name of Grace’s and Red-faced Warbler survey routes and type and extent of suitable habitat in the Jemez Mountains, Jemez Ranger District, Santa Fe National Forest, New Mexico.




Appendix A. Species detected during surveys, listed in taxonomic order, and their NMDGF conservation status.

Common Name Scientific Name NMDGF status*

Species detected by location Jemez Manzano Magdalena Sandia San Mateo Zuni

Montezuma Quail Cyrtonyx montezumae SGCN, Tier 3 X

Wild Turkey Meleagris gallopavo X X X X X X

Turkey Vulture Cathartes aura X X X X X X

Cooper's Hawk Accipiter cooperii X X

Northern Goshawk Accipiter gentilis SGCN X

Red-tailed Hawk Buteo jamaicensis X X X X

Band-tailed Pigeon Patagioenas fasciata SGCN, Tier 2 X X X X

White-winged Dove Zenaida asiatica X X X X

Mourning Dove Zenaida macroura SGCN, Tier 3 X X X X X X

Flammulated Owl Psiloscops flammeolus SGCN, Tier 2 X X X

Great Horned Owl Bubo virginianus X

Northern Pygmy-Owl Glaucidium gnoma X

Mexican Spotted Owl Strix occidentalis lucida SGCN, Tier 1 X

White-throated Swift Aeronautes saxatalis X X

Black-chinned Hummingbird Archilochus alexandri X X

Broad-tailed Hummingbird Selasphorus platycercus X X X X X X

Acorn Woodpecker Melanerpes formicivorus X X X

Williamson's Sapsucker Sphyrapicus thyroideus SGCN, Tier 3 X

Red-naped Sapsucker Sphyrapicus nuchalis X X X X

Downy Woodpecker Picoides pubescens X X X X X X

Hairy Woodpecker Picoides villosus X X X X X X

American Three-toed Woodpecker Picoides dorsalis X

Northern Flicker Colaptes auratus X X X X X X

American Kestrel Falco sparverius X

Peregrine Falcon Falco peregrinus SGCN, Tier 2 X

Olive-sided Flycatcher Contopus cooperi SGCN, Tier 2 X X X X




Western Wood-Pewee Contopus sordidulus X X X X X X

Hammond's Flycatcher Empidonax hammondii X

Dusky Flycatcher Empidonax oberholseri X

Cordilleran Flycatcher Empidonax occidentalis X X X X X X

Unknown Empidonax Flycatcher Empidonax X X X

Say's Phoebe Sayornis saya X X

Ash-throated Flycatcher Myiarchus cinerascens X X X X X X

Western Kingbird Tyrannus verticalis X

Plumbeous Vireo Vireo plumbeus X X X X X X

Warbling Vireo Vireo gilvus X X X X X X

Pinyon Jay Gymnorhinus cyanocephalus SGCN, Tier 2 X X X

Steller's Jay Cyanocitta stelleri X X X X X X

Clark's Nutcracker Nucifraga columbiana SGCN, Tier 2 X X X

Common Raven Corvus corax X X X X X X

Tree Swallow Tachycineta bicolor X X X X

Violet-green Swallow Tachycineta thalassina X X X X

Mountain Chickadee Poecile gambeli X X X X X X

Juniper Titmouse Baeolophus ridgwayi SGCN, Tier 2 X

Bushtit Psaltriparus minimus X X X X

Red-breasted Nuthatch Sitta canadensis X X X X X X

White-breasted Nuthatch Sitta carolinensis X X X X X X

Pygmy Nuthatch Sitta pygmaea SGCN, Tier 3 X X X X X

Brown Creeper Certhia americana X X X X X X

Canyon Wren Catherpes mexicanus X X

House Wren Troglodytes aedon X X X X X

Bewick's Wren Thryomanes bewickii X X

Blue-gray Gnatcatcher Polioptila caerulea X X

Golden-crowned Kinglet Regulus satrapa X X

Ruby-crowned Kinglet Regulus calendula X X X X X X

Western Bluebird Sialia mexicana SGCN, Tier 2 X X X X




Townsend's Solitaire Myadestes townsendi X X X X X

Hermit Thrush Catharus guttatus X X X X X X

American Robin Turdus migratorius X X X X X X

Orange-crowned Warbler Oreothlypis celata X X X X X X

Virginia's Warbler Oreothlypis virginiae SGCN, Tier 2 X X X X X

MacGillivray's Warbler Geothlypis tolmiei X X X X X

Yellow-rumped Warbler Setophaga coronata X X X X X X

Grace's Warbler Setophaga graciae SGCN, Tier 2 X X X X X X

Black-throated Gray Warbler Setophaga nigrescens SGCN, Tier 2 X X X

Townsend's Warbler Setophaga townsendi X X

Wilson's Warbler Cardellina pusilla X X X X

Red-faced Warbler Cardellina rubrifrons SGCN, Tier 3 X X

Painted Redstart Myioborus pictus SGCN, Tier 3 X

Green-tailed Towhee Pipilo chlorurus X

Spotted Towhee Pipilo maculatus X X X X X X

Chipping Sparrow Spizella passerina X X X X X X

Black-chinned Sparrow Spizella atrogularis SGCN, Tier 2 X

Dark-eyed Junco Junco hyemalis X X X X X X

Hepatic Tanager Piranga flava X X

Summer Tanager Piranga rubra X

Western Tanager Piranga ludoviciana X X X X X X

Black-headed Grosbeak Pheucticus melanocephalus X X X X X X

Brown-headed Cowbird Molothrus ater X X

House Finch Haemorhous mexicanus X

Cassin's Finch Haemorhous cassinii SGCN, Tier 2 X

Pine Siskin Spinus pinus X X X X X X

Lesser Goldfinch Spinus psaltria X X X

Evening Grosbeak Coccothraustes vespertinus SGCN, Tier 2 X *Species of Greatest Conservation Need (SGCN) and tier based on conservation urgency: Tier 1 = most urgent, Tier 2 = moderately urgent, and Tier 3 = leasturgent (NMDGF 2015)




Appendix B. Species relative abundance by site, and total abundance and diversity measures for each site including total number of individuals recorded, total abundance, Shannon’s index, evenness, and species richness.

Common Name Relative abundance (%) by location - Percent of total

Jemez Manzano Magdalena Sandia San Mateo Zuni Montezuma Quail 0.347 Wild Turkey 0.060 0.750 0.455 0.475 1.109 0.081 Turkey Vulture 4.450 0.173 2.729 0.416 0.208 0.081 Cooper's Hawk 0.241 0.115 Northern Goshawk 0.139 Red-tailed Hawk 0.120 0.231 0.059 0.069 Band-tailed Pigeon 0.120 0.058 0.416 0.889 White-winged Dove 0.120 0.834 1.426 0.081 Mourning Dove 0.241 0.807 0.758 1.426 0.069 0.081 Flammulated Owl 0.060 0.058 0.081 Great Horned Owl 0.076 Northern Pygmy-Owl 0.120 Mexican Spotted Owl 0.208 White-throated Swift 0.782 0.076 Black-chinned Hummingbird 0.058 0.119 Broad-tailed Hummingbird 2.526 1.557 4.094 8.378 1.455 2.423 Acorn Woodpecker 0.227 1.663 0.081 Williamson's Sapsucker 0.120 Red-naped Sapsucker 0.115 0.152 0.535 0.646 Downy Woodpecker 1.143 0.807 0.834 0.713 0.762 0.646 Hairy Woodpecker 0.842 0.980 1.213 0.951 1.317 0.081 American Three-toed Woodpecker 0.060 Northern Flicker 2.526 2.307 2.123 1.842 3.812 2.181 American Kestrel 0.208 Peregrine Falcon 0.069 Olive-sided Flycatcher 0.060 0.115 0.152 0.059 Western Wood-Pewee 0.722 1.615 1.820 1.188 0.416 0.404 Hammond's Flycatcher 0.541 Dusky Flycatcher 0.058 Cordilleran Flycatcher 4.149 3.518 4.776 1.129 4.435 3.312 Unknown Empidonax Flycatcher 0.120 0.076 0.069 Say's Phoebe 0.060 0.119 Ash-throated Flycatcher 0.301 0.231 1.365 1.188 0.277 0.404 Western Kingbird 0.059 Plumbeous Vireo 2.165 2.595 8.415 6.239 1.663 1.050 Warbling Vireo 3.608 4.325 3.260 1.664 0.832 0.565




Pinyon Jay 0.152 0.475 5.250 Steller's Jay 3.848 3.172 2.350 4.159 7.484 7.270 Clark's Nutcracker 2.285 0.277 0.485 Common Raven 2.165 1.499 0.758 0.654 1.733 6.947 Tree Swallow 0.541 0.058 0.178 0.139 Violet-green Swallow 0.842 0.404 0.119 0.081 Mountain Chickadee 5.232 8.939 6.520 8.913 7.554 8.966 Juniper Titmouse 0.119 Bushtit 0.519 1.516 0.594 0.208 Red-breasted Nuthatch 0.722 0.519 1.213 1.307 0.901 1.939 White-breasted Nuthatch 3.367 1.615 2.199 4.100 2.911 0.889 Pygmy Nuthatch 3.307 0.346 0.594 3.673 3.069 Brown Creeper 0.782 0.288 0.076 0.238 1.178 0.081 Canyon Wren 0.060 0.758 House Wren 0.120 0.607 0.475 1.940 0.162 Bewick's Wren 0.058 0.076 Blue-gray Gnatcatcher 3.184 0.069 Golden-crowned Kinglet 0.060 0.139 Ruby-crowned Kinglet 5.111 1.845 0.303 0.772 1.733 1.939 Western Bluebird 2.076 0.531 1.317 1.212 Townsend's Solitaire 0.301 0.173 0.152 0.416 1.535 Hermit Thrush 5.713 7.497 4.549 3.565 4.435 5.977 American Robin 6.314 10.265 2.805 3.684 7.277 3.150 Orange-crowned Warbler 0.601 0.750 0.152 0.059 0.069 0.081 Virginia's Warbler 0.361 0.173 0.834 0.951 0.347 MacGillivray's Warbler 0.421 0.346 0.682 1.307 0.242 Yellow-rumped Warbler 4.209 4.729 2.805 4.575 1.802 1.939 Grace's Warbler 7.096 9.631 5.155 7.011 3.119 7.351 Black-throated Gray Warbler 0.231 0.531 0.297 Townsend's Warbler 0.059 0.069 Wilson's Warbler 0.060 0.058 0.152 0.297 Red-faced Warbler 3.184 5.544 Painted Redstart 0.531 Green-tailed Towhee 0.058 Spotted Towhee 1.443 5.190 6.065 4.694 2.772 0.889 Chipping Sparrow 2.946 2.076 2.047 1.367 0.277 0.969 Black-chinned Sparrow 0.303 Dark-eyed Junco 3.909 4.902 1.137 2.139 6.930 3.473 Hepatic Tanager 0.058 0.986 Summer Tanager 0.115 Western Tanager 4.931 6.978 8.795 5.764 2.841 6.947




Black-headed Grosbeak 3.127 3.979 4.246 6.952 2.218 8.320 Brown-headed Cowbird 0.379 0.772 House Finch 0.152 Cassin's Finch 0.058 Pine Siskin 4.630 0.923 0.379 5.645 11.088 7.674 Lesser Goldfinch 0.241 0.303 0.178 Evening Grosbeak 0.081

Total individuals of all species 1663 1734 1319 1683 1443 1238 Total abundance of all species

combined (individuals/ha) 4.010 3.704 3.087 4.252 3.281 3.153 Shannon's index 3.417 3.191 3.444 3.302 3.281 3.134

Evenness 0.853 0.804 0.856 0.840 0.834 0.828 Species richness 55 53 56 51 51 44


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