volume 13, 2003 british columbia birdsvolume 13, 2003 british columbia birds page 1 contents observ...

Volume 13, 2003 British Columbia Birds Page 1

CONTENTS

OBSERV ATIONS OF NEST PREDATION BY COOPER' S HAWKS ON VANCOUVER ISLAND,BRITISH COLUMBIA

BOOK REVIEWS

BIRDS OF THE YUKON TERRITORY, edited by Pamela H. Sinclair, Wendy A. Nixon, Cameron D. Eckert and Nancy L. HughesReviewed by John B. Sprague 11

COMMON BIRDS OF BRITISH COLUMBIA, by J. Duane SeptReviewed by John Vooys 12

BEGINNERS GUIDE TO B.C. BIRD SONG, by John Neville and Mel CoulsonReviewed by Lloyd Esralson 12

BIRDS OF COASTAL BRITISH COLUMBIA, by Nancy Baron and John AcornReviewed by Michael Price 14

SEABIRD BYCATCH: TRENDS, ROADBLOCKS, AND SOLUTIONS, edited by Edward F. Melvin and Julia K. Parrish.Reviewed by Alan E. Burger 15

NESTBOXES FOR PRAIRIE BIRDS, by Myrna PearmanReviewed by Eva Durance 17

BIRD SOUNDS B WESTERN BOREAL FOREST, by John NevilleReviewed by Russell Tkachuk 18

THE BIRD ALMANAC: A GUIDE TO ESSENTIAL FACTS AND FIGURES OF THE WORLD'S BIRDS, by David M. BirdReviewed by R.A. (Andy) Buhler 18

BIRDS OF THE RAINCOAST, by Harvey Thommasen and Kevin Hutchings, with R. Wayne Campbell and Mark HurneReviewed by Barbara Begg 19

BIRD ECOLOGY AND CONSERVATION: A HANDBOOK OF TECHNIQUES, by William J. Sutherland,Ian Newton and Rhys E. GreenReviewed by Phil Henderson 21

THE SPECIATION AND BIOGEOGRAPHY OF BIRDS, by Ian NewtonReviewed by Phil Henderson 23

EXPLORING ALASKA'S BIRDS, by Alaska Geographic SocietyReviewed by Stephen R. Johnson 25

MOUNTAIN BLUEBIRD TRAIL MONITORING GUIDE, by Myrna PearmanReviewed by Katie Aitken 25

A BIRDER'S GUIDE TO WASHINGTON, by Hal OppermanReviewed by Lloyd Esralson 26

ACKNOWLEDGEMENTS 28

DO BLACK-THROATED GREEN WARBLERS IN NORTHEAST B.C. REQUIRE RIPARIAN FOREST?Mark Phinney . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

NOTES ON PARENTAL CARE BY CASSIN'S VIREOSJanice Arndt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Andrew C. Stewart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

PURPLE FINCHES FEED ON WILLOW CATKINSAI Grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

APPARENT HYBRID LINCOLN'S X SONG SPARROW AT BOUNDARY LAKEChris Charlesworth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

British Columbia Birds Volume 13, 2003

DO BLACK-THROATED GREEN WARBLERS IN NORTHEAST B.C. REQUIRE RIPARIAN FOREST?

Mark Phinney

Louisiana-Pacific Canada Ltd Dawson Creek, B.C. V1G 3CB

[email protected]

Abstract -- Literature about Black-throated Green Warblers in British Columbia generally states that the species requires riparian habitat. This was not my impression during bird surveys in the Peace River district. This study showed that warblers were farther from water than were random points. There was a significant (p<0.001) difference between (a) distances from singing Black-throated Green Warblers to the nearest waterbody (n = 262, average distance = 270 m), and (b) distances from randomly selected points to the nearest waterbody (n = 300, average distance = 188 m). Apparently this species avoids riparian habitat in northeastern British Columbia. Key words: Black-throated Green Warbler, Dendroica virens, riparian, habitat, Peace River, British Columbia, survey, preference, selection, forest type. INTRODUCTION

The Black-throated Green Warbler (Dendroica virens, hereafter B-t Green Warbler) is a relatively recent addition to the avifauna of B.C.; having colonized the Peace River area from neighbouring Alberta during the latter half of the 1900s (Campbell et al. 2001). The species is currently ‘Blue-Listed’ (of Special Concern) in both provinces (Alberta 2001; B.C. 2003). As a species of management interest in both provinces, numerous status reports have been compiled, which summarize information on the species’ life history and habitat requirements. The majority of reports for B.C. emphasize the need for riparian mixedwood forests (mixed conifer and deciduous) as breeding habitat (e.g. Enns and Siddle 1996; Cooper et al. 1997; Blood and Barkhouse 1998; Fraser et al. 1999; Campbell et al. 2001). Alberta reports are in agreement with the requirement for mature mixedwood forest, but mention the riparian aspect only in passing (Semenchuk 1992; Norton 1999). See Collins (1983) and Morse (1993), however, for discussion on the range of forested habitats used by this species in eastern and central North America.

During the past 14 years I have done bird surveys in the Peace River area of northeastern B.C., and this has led me to believe that the B-t Green Warbler is not at all dependent on riparian forest. In fact, the highest densities I have encountered were in mature/old aspen-spruce mixedwood stands on upland sites. General perceptions can be misleading, however, so I tested the concept as outlined in this paper. METHODS

If B-t Green Warblers are dependent on riparian forest, then they should be found closer to waterbodies (on average) than are random locations. Therefore I tested distances from identified bird locations to the nearest waterbody, against distances for random points in the same area.

Locations for 262 male B-t Green Warblers, as determined by Global Positioning System (GPS) were extracted from an existing data set of Red- and Blue-listed warbler locations. These locations were not detected through random sampling. Rather, large areas that were of forest management interest (i.e. containing harvestable timber) were selected, and logging roads, seismic lines, pipelines and other trails were used as transects, along which surveys were conducted. The transects were traversed by foot, bicycle, all-terrain vehicle or pickup truck. Efforts were made to reduce the effect of vehicle noise on detection of birds. For example, a stop was made every 100 m in order to listen for 20-30 seconds.

Warbler songs could easily be heard over 50 m away, so there were no ‘gaps’ in coverage. When a warbler was heard singing, the surveyor found and marked the tree it was singing from, then continued on to the next bird. GPS location and vegetation sampling was done at a later date in order to maximize survey time during the relatively brief singing period. This procedure was adopted because the purpose of the original survey was to document the presence of selected bird species, particularly B-t Green Warblers and Connecticut Warblers (Oporornis agilis), within the areas of management interest, but not necessarily to detect all birds along the survey route. In addition, the survey gathered information on habitat being used in these areas. The two species of particular interest occupy different habitats.

For comparison purposes, a number of random point locations were generated within the same range of latitude and longitude as the warbler points. This was done with a random number generator which creates Universal Transverse Mercator coordinates. Both data sets were then plotted in relation to waterbody information provided by B.C. TRIM (Terrain Resource Information Mapping) using ARCVIEW® geographic information system. An example is presented in Figure 1. All TRIM rivers, creeks, lakes and wetlands were considered as ‘sources’ of riparian areas. The width of specific riparian areas is unknown in this exercise; tiny trickles may flow through a broad drainage


and have a relatively wide riparian influence. Conversely, large rivers may flow through steep gorges and have minimal riparian influence on forests high above. Field experience has shown that a small proportion of TRIM creeks do not actually exist on the ground; apparently because of errors in aerial photo interpretation. In these cases, however, there is always an identifiable drainage pattern and low-lying ground, often with riparian characteristics -- even without surface water. The reverse case of an existing stream missing from TRIM data is extremely rare.

Thus, as a measure of the warbler’s affinity for riparian areas, the distance from each bird location to the nearest TRIM waterbody was measured (to the line indicating streams or nearest edge of river, lake or wetland). The same procedure was then repeated for all of the random points (see Figure 2). All measurements were done at an approximate scale of 1:1000. Potential Bias:

There are several potential sources of bias associated with this manner of identifying locations. Are the birds representative? While it is possible that some birds were migrating or not singing on territory, the surveys were conducted between late May and late June, when most B-t Green Warblers should be establishing or defending territories in acceptable habitat. All habitats along the transects were surveyed, i.e. the surveyor did not ‘skip’ habitat that looked ‘unsuitable’. It might be argued that the transect locations were biased, because roads typically avoid riparian areas. There appeared to be no consistent bias in this regard. While some roads might avoid low-lying areas as a general route, they can also cross many streams. Some roads actually ran parallel to watercourses.

Some factors reduced the potential bias. Warblers were frequently detected a considerable distance from the transect. Subsequent detections were also common (birds that could not be detected from the road were heard farther off once the surveyor had reached the ‘original’ singing bird). Thus, the sample width of the transects was variable, and not limited to ~50 m. In addition, potential bias associated with road locations becomes irrelevant when considering seismic lines and pipelines, which were also used as transects. Readers from other areas might think that the sound of running water in riparian areas would drown out the warbler songs, thereby reducing the number of detections near water. In reality, few of the creeks or rivers presented a noise problem. The terrain in the study area has rather gentle relief, and water flow is usually low and slow (aside from springtime runoff and after a major rain). Accordingly, although the sampling strategy was ‘haphazard’ rather than random, there does not appear to be any procedural reason for the warbler locations to be systematically biased with regard to distance from riparian areas. It is unlikely that warblers are randomly distributed across a natural landscape; they are almost certainly clumped in areas of suitable habitat.

Figure 1. Mapsheet 93P.065 showing all TRIM waterbodies. Murray

River is on the left, with Coldstream Creek at top and bottom right. Ten dots represent warbler locations, while three stars represent random locations. Area within the box is shown at smaller scale below.

Figure 2. Close-up view of a section of Figure 1. In this case, the

random point was found to be 66 m from the nearest waterbody, while the warbler was found to be 140 m away.

RESULTS

The mean distance-to-water for warbler locations was 270 m (n = 262) while the mean distance for random points was 188 m (n =300, see Figure 3). This is a significant difference (p <0.001; t-test with unequal variances). The 95% confidence limits do not overlap (Figure 4). This result indicates an avoidance of waterbodies (and associated riparian zones) rather than a preference. Even if there had been no statistical difference between the means, the null hypothesis of ‘no difference’ would not have been rejected and there would again have been no evidence to suggest warbler preference of riparian forest.


Figure 3. Proportions of warbler locations and random locations at

various distances from water.

Figure 4. Mean distances to TRIM waterbody, plus and minus 95%

confidence limits. DISCUSSION

The results suggest that B-t Green Warblers may be avoiding riparian habitat; at least warbler locations are situated farther from waterbodies than random points. This is a surprising result, because the species has been documented in riparian habitat (Enns and Siddle 1996). To further investigate the possibility of avoidance, it would be useful to document warbler habitat use in blocks of forest containing both riparian and upland habitat.

Until then, however, and in light of the findings from this study, it is worth considering two questions: (1) Why would B-t Green Warblers avoid riparian forest? and (2) Why does so much of the B.C. literature claim the opposite? I can only speculate on the answers.

Riparian habitat exists as a band of moisture-influenced vegetation extending outward from a waterbody. This band may be less than a metre or over 100 m in width, depending on a number of factors. In any case, however, it tends to be longer than it is wide (e.g. a ring around a lake or wetland,

or a strip along a stream or river). The linear nature of the habitat means that there is a higher edge-to-area ratio than for non-linear habitat blocks. It has been suggested that B-t Green Warblers avoid edges and prefer ‘interior’ forest conditions (Germaine et al. 1997; Norton 1999). Thus, although the tree species found in riparian habitats may be suitable, it is possible that there is insufficient ‘core’ habitat in many cases. The argument is admittedly tenuous, however, since locally I have noticed no obvious avoidance of abrupt or subtle edges by this species (except in agricultural landscapes; e.g. Hobson and Bayne 2000). See also Blood and Backhouse (1998).

There is no question that some B-t Green Warblers occupy riparian mixedwood habitat in northeastern British Columbia. How this came to be known as the primary or required habitat in the B.C.-based literature is uncertain. Part of the reason likely stems from the general scarcity of published literature on the topic; a few papers are cited frequently, and statements are perpetuated. Most of the B-t Green Warbler habitat citations can be traced back to Enns & Siddle (1996) and Francis and Lumbis (1979). Enns & Siddle (1996) tallied 50 Black-throated Green Warblers during 33 field days in 1992 (some of this time was spent outside the geographic range of the warbler). About half of the B-t Green Warblers encountered were found in riparian habitat - just as many were found in upland mixedwood habitat, yet the “proposed habitat model” for the species includes only “mixed, tall white spruce and poplar stands within the Boreal White Spruce-Balsam Poplar Riparian habitat type”. Was omission of upland habitats an oversight? The often-cited report by Francis and Lumbis (1979) states that two territories were found in riparian balsam poplar / aspen forest with a few scattered tall white spruce.

A related factor is that much of the past work on northeastern B.C. birds (especially the Red- and Blue-listed species) has been done by visitors to the area, often working under time constraints. There is a tendency to look for the species where it is ‘expected’ (that being mature riparian mixedwood forest, according to the literature) and the entire exercise becomes a self-fulfilling prophecy. These issues are acknowledged by Enns and Siddle (1996). That the species is typically considered ‘uncommon and local’ (e.g. Campbell et al. 2001) supports the notion that assessments are made by evaluating its status within this ‘expected’ habitat, where it is uncommon and local. The species is actually common and quite widespread in the region (Phinney 1998, South Peace Bird Atlas Society, unpublished data).

Confirming that B-t Green Warblers in northeastern B.C. are not dependent on riparian forest has implications for managing the species within the province. The status of the species is not as tenuous as was once thought, and more effective habitat modelling and management is now possible. Despite this more optimistic status assessment, there are still factors that warrant continued concern for the species in B.C. The B-t Green Warbler appears to have the


most limited distribution of any ‘listed’ warbler in northeastern B.C., being largely restricted to the Peace River area. There are records from farther north at Tuchodi River, but the status of the species in that area is uncertain (Campbell et al. 2001; Cooper et al. 1997). Timber harvesting will have a detrimental effect on warbler numbers. Most plans call for rotation ages in managed forests to be less than the ages of stands currently used by this species. In addition, government policy effectively prohibits the re-establishment of ‘salt and pepper’ mixedwood forest that the warbler prefers. Instead of mixedwood, pure coniferous or deciduous stands are regenerated, limiting future B-t Green Warbler habitat to the interface of these stand types. Thus, it seems certain that the local population of this species will ultimately decline, but it is doubtful that it will disappear from the province altogether. LITERATURE CITED Alberta 2001. List of species currently listed under the

wildlife act and new species assessed by the Alberta Endangered Species Conservation Committee since its inception. Alberta Endangered Species Conservation Committee, Edmonton, Alta.

http://www3.gov.ab.ca/srd/fw/escc/aaisar_1.html B.C. 2003. Species and Ecosystems Explorer. Government

of British Columbia, Victoria, B.C. http://srmapps.gov.bc.ca/apps/eswp/ Blood, D.A. and F. Barkhouse. 1998. Rare warblers of

northeastern British Columbia. B.C. Ministry of Environment, Lands, and Parks, Wildlife Branch, Victoria, B.C. 6 p.

Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M.

Cooper, G.W. Kaiser, A.C. Stewart, and M.C.E. McNall. 2001. The birds of British Columbia, Vol. IV. UBC Press, Vancouver, B.C. 739 p.

Collins, S.L. 1983. Geographic variation in habitat structure

of the Black-throated Green Warbler (Dendroica virens). Auk 100:382-389.

Cooper, J.M., K.A. Enns, and M.G. Shepard. 1997. Status

of the Black-throated Green Warbler in British Columbia. B.C. Ministry of Environment, Lands and Parks, Wildlife Working Report WR-80. Victoria, B.C. 24 + x p.

Enns, K.A. and C. Siddle. 1996. The distribution, abundance and habitat requirements of selected passerine birds of the Boreal and Taiga Plains. B.C. Ministry of Environment, Lands and Parks, Wildlife Branch, Victoria, B.C. Wildlife Working Report WR-76. 44 p.

Francis, J. and K. Lumbis. 1979. Habitat relationships and management of terrestrial birds in northeastern Alberta. AOSERP Report No. 78, Alberta Oil Sands Environmental Research Program, Canadian Wildlife Service, Edmonton, Alta. 365 p.

Fraser, D.F., W.L. Harper, S.G. Cannings, and J.M. Cooper.

1999. Rare birds of British Columbia. B.C. Ministry of Environment, Lands, and Parks, Wildlife Branch and Resource Inv. Branch, Victoria, B.C. 244 p.

Germaine, S.S., S.H. Vessey, and D.E. Capen. 1997.

Effects of small forest openings on the breeding bird community in a Vermont hardwood forest. Condor 99:708-718.

Hobson, K.A. and E. Bayne. 2000. Effects of forest

fragmentation by agriculture on avian communities in the southern boreal mixedwoods of western Canada. Wilson Bulletin: 112:373-387.

Morse, D. H. 1993. Black-throated Green Warbler

(Dendroica virens). In A. Poole and F. Gill (Editors). The Birds of North America, No. 55. The Birds of North America, Inc., Philadelphia, Pa.

Norton, Michael R. 1999. Status of the Black-throated

Green Warbler (Dendroica virens) in Alberta. Alberta Environment, Fisheries and Wildlife Management Division, and Alberta Conservation Association, Wildlife Status Report No. 23, Edmonton, Alta.. 24 p.

Phinney, Mark. 1998. Spring and summer birds of Dawson

Creek 1991-1995. Wild Bird Trust of British Columbia, Wildlife Report No.4. 63 p.

Semenchuck, Glen. P. 1992. The atlas of breeding birds of

Alberta. Federation of Alberta Naturalists, Edmonton, Alta. 297 p.

Black-throated Green Warbler / Bill Heybroek


NOTES ON PARENTAL CARE BY CASSIN’S VIREOS

Janice Arndt 901 Highway 3A

Nelson BC V1L 6J5 Abstract -- A pair of Cassin’s Vireos were observed at their nest near Nelson, British Columbia. Both the male and female brooded and fed the nestlings. Shared parental care has not previously been reported for this species. Key words: behaviour, breeding, Cassin’s Vireo, Kootenay region, parental care, Vireo cassinii

Cassin’s Vireo (Vireo cassinii) was until recently considered to be a western subspecies of the widespread Solitary Vireo (V. solitarius). Molecular genetic studies (Murray et al. 1994, Johnson 1995) showed sufficient differences for the Solitary Vireo complex to be split into three distinct species: Cassin’s Vireo in western North America, Blue-headed Vireo (V. solitarius) in the north and east, and Plumbeous Vireo (V. plumbeus) in the southwestern portion of its range (AOU 1997). Prior to splitting, most behavioural studies of Solitary Vireo appear to have been performed on the eastern and southwestern forms; consequently, there are major gaps in our knowledge of Cassin’s Vireo life history (Goguen and Curson 2002).

On 31 May 2004, I located an active Cassin’s Vireo nest near Nelson, British Columbia. The nest was placed 2.0 m off the ground in a twig fork of a Douglas Maple (Acer glabrum) sapling and was poorly concealed. An adult was incubating four eggs. When I returned to the nest on 2 June the presumed male (based on singing behaviour) of the pair was singing overhead while the presumed female was incubating. Over the next five minutes the male descended toward the nest and continued singing until it alighted in the nest tree. The female left the nest and the male settled into it to incubate.

On the afternoon of 3 June the nest contained one egg and three young. Both adults were present. The bird in the nest continued brooding for 15 min after my arrival, then the second bird came with food, fed one or more chicks, and brooded for nearly 15 min. The first bird returned with food, fed a chick, and brooded for 40 minutes, after which I left. The sex of the individuals was not known during these observations but it was clear that both members of the pair participated in the brooding and feeding of the young.

I continued to observe the nest, making six more visits between 4 and 14 June. Brooding continued until at least 8 June and both adults fed the young throughout the nestling period. Once, I saw an adult vireo remove a faecal sac. On 15 June the four young were huddled inside the nest. On the following day the nest was empty and fresh droppings were found on the ground below. Although I searched the area for several minutes, I did not see any fledgling vireos. However, the pair scolded me vigorously and one adult was carrying food. In addition, one bird fluttered its wings as if begging in an apparent distraction display, while the other flew at my head and snapped its beak.

The account for Cassin’s Vireo in the Birds of North America indicates a lack of information on many aspects of the species’ biology, particularly its breeding behaviour (Goguen and Curson 2002). While incubation by both adults was reported, it was not known whether one or both provided care of the young after hatching. Under the section titled “Parental Care”, the statement “no information” occurs in all three subheadings: brooding, feeding, and nest sanitation. Cassin’s Vireo was assumed to behave similarly to the closely related Plumbeous and Blue-headed vireos, in which both adults care for young, but those details had not been confirmed at the time of the publication of the Cassin’s account (Goguen and Curson 2002). Although based on a single pair of unmarked birds, my observations show that male and female Cassin’s Vireos share the feeding and brooding of young in the nest. In addition, one of the pair was observed to remove a faecal sac to provide nest sanitation. The four young likely hatched on 3 June and left the nest 16 June, indicating a fledgling period of approximately 13 days which falls within the range of 11-15 days noted by Goguen and Curson (2002).

Many aspects of the life history of Cassin’s Vireo remain poorly known, providing birders in British Columbia with an unusual opportunity to make significant contributions to the knowledge of this species’ biology. LITERATURE CITED American Ornithologists’ Union. 1997. Forty-first

supplement to the American Ornithologists’ Union Check-list of North American Birds. Auk 114:542-552.

Goguen, C.B. and D.R. Curson. 2002. Cassin’s Vireo

(Vireo cassinii). In A. Poole and F. Gill (Editors). The Birds of North America, No. 615. The Birds of North America, Inc., Philadelphia, Pa.

Johnson, N.K. 1995. Speciation in vireos. I.

Macrogeographic patterns of allozymic variation in the Vireo solitarius complex in the contiguous United States. Condor 97:903-919.

Murray, B.W., W.B. McGillivray, J.C. Barlow, R.N. Beech

and C. Strobeck. 1994. The use of cytochrome B sequence variation in estimation of phylogeny in the Vireonidae. Condor 96:1037-1054.


OBSERVATIONS OF NEST PREDATION BY COOPER’S HAWKS ON VANCOUVER ISLAND, BRITISH COLUMBIA

Andrew C. Stewart

3932 Telegraph Bay Road Victoria, B.C. V8N 4H7

Abstract -- Nest predation by Cooper's Hawks (Accipiter cooperii) is rarely observed and has largely been inferred from prey deliveries or bird remains found at hawk nests. Here I describe two independent observations of breeding male Cooper’s Hawks raiding nests of American Robin (Turdus migratorius) on southern Vancouver Island, British Columbia. Key words: nest predation, Cooper’s Hawk, Accipiter cooperii, American Robin, Turdus migratorius, Vancouver Island.

Juvenile birds and mammals comprise a significant proportion of the breeding diet of the Cooper’s Hawk (Accipiter cooperii) across its North American range (Rosenfield and Bielefeldt 1993). In Michigan, 74% of avian prey deliveries and bird remains found at Cooper’s Hawk nest sites were young of the year, of which 10% were nestlings (Bielefeldt et al. 1992). Meng (1959) twice observed a male Cooper's Hawk delivering passerine nestlings to its own young. Nest-robbing is likely a common foraging tactic employed by this hawk during the breeding period, but has rarely been observed. Linduska (1943) and Nelson (1968) reported the only direct observations of nest predation by this accipiter. Increasingly, nest cameras are being employed by researchers to help determine the causes of passerine nest failures. In some of these studies, accipiters have been shown to be an important nest predator (McCallum and Hannon 2001, Williams and Wood 2002). Here I describe two direct observations of nest predation by different breeding male Cooper’s Hawks in urban Greater Victoria, on southern Vancouver Island, British Columbia (48˚ 27´N, 123˚ 20´W).

The first observation occurred on 19 July 1997 while I monitored an active Cooper’s Hawk nest site located in a wooded area on the campus of the University of Victoria. Both parents were present and actively feeding their four fledged but still dependent young. At 10:35 PST, while watching one of these fledglings eat a recently delivered American Robin (Turdus migratorius) nestling, my attention was drawn to the agitated calls of a pair of adult robins located about 50 m away in a wooded ravine. Through binoculars I could see an unbanded adult male Cooper’s Hawk perched on a limb near the broken top of a 6-metre-tall snag. About 40 cm from this hawk was a robin nest built amongst the ivy-covered trunk of the snag. The hawk faced the nest, but appeared distracted by the parent robins which were both repeatedly diving at it. At one point the hawk made a “ka-ka-ka” call, presumably in response to this harassment. Within seconds it abruptly moved towards the nest, snatched a nestling in one of its talons, and immediately departed with both adult robins in close pursuit. The hawk flew quickly from view and at 10:38 I heard the excited begging calls of fledgling hawks on the edge of the ravine, suggesting a prey delivery had occurred. Although unable to observe these hawks from my location,

I presumed the adult male had delivered the nestling I had just seen taken from its nest. The robin nest was located approximately 170 m away from the Cooper’s Hawk nest tree and was just beyond the area that the fledgling hawks had been observed to range.

On inspection, the robin’s nest still contained a single

nestling estimated to be about 9 days of age. The surviving young appeared to be of the same age class as the nestling I had observed earlier (10:28 - 10:35) being eaten by a fledgling hawk and had possibly been taken from this same nest. From 10:40 - 12:00, I continued to monitor the robin nest from a distance to determine if the Cooper’s Hawk would return for the remaining nestling. The hawk did not return during this period and the nestling was still present in its nest when last checked at 20:00 the following day.

The second nest-robbing incident occurred on 27 July 1997 near my residence in the Cadboro Bay area of Saanich. As in the first predation event, my attention was initially drawn by alarm calls of an adult American Robin, as well as several Chestnut-backed Chickadees (Poecile rufescens). These birds were located about 30 m away from me in a neighbouring yard. On closer investigation, a colour-banded adult male Cooper’s Hawk was observed perched in the top of a low tree. The hawk flew between several trees and appeared to be actively hunting. From the distressed behaviour of the robin, I presumed it had young close by. The hawk did not appear to have located its intended prey when first observed and may have been cueing on the excited response of this solitary adult robin. At 15:00, as I watched it through binoculars, the hawk disappeared into the foliage to emerge moments later with a robin-sized bird in its talons. It quickly flew from view with the adult robin pursuing it. Less than 1 minute later I saw the hawk emerge from cover carrying its prey in the direction of its own nest, located approximately 375 m distant. This marked hawk was known to have three dependent fledglings.

Following the hawk’s departure, I checked the area and found a robin nest situated about 5.5 m above the ground in a small tree. At 15:13, while inspecting the contents of this nest with a pole-mirror, the hawk returned to within about 1 m of the nest but was apparently frightened away by the mirror. On this second visit, the hawk flew directly to the


robin nest from the general direction of its own nest. Close inspection of the nest revealed a solitary nestling, which I estimated to be about 10 days of age. Unfortunately, I was unable to continue monitoring this nest but when I rechecked it at 17:35 the following day, it was empty, with no sign of an adult robin in the vicinity. Presumably the hawk had returned to take this last nestling, as it was too young to have fledged during the intervening period.

The perch-and-scan hunting technique employed by the Cooper’s Hawk is an effective and economical method of finding prey and may predispose active passerine nests to detection by this predator (Bielefeldt et al. 1992). Robin nestlings are fed at a rate of 35 - 40 times/day and become more vocal with age (Sallabanks and James 1999). Research on other passerines has shown that predation risk increases with nestling age (Pietz and Granfors 2000), possibly the result of an increased rate of parental feeding and more vocal young.

In both of these predation events, the parents were present but ineffective in preventing predation of their nests. Moreover, parental behaviour in the second incident may have assisted the hawk in locating the nest. Robins with recently fledged young behave similarly (personal observation) and through experience Cooper’s Hawks probably learn to exploit this behaviour to locate these vulnerable prey. As was demonstrated in the latter incident, once occupied nests are discovered, breeding hawks may return until all young are taken thereby maximizing their own reproductive efforts. Male Cooper’s Hawks do most of the hunting during the breeding period (Meng 1959, Rosenfield and Beilefeldt 1993) and nest-robbing could be a common foraging strategy employed by this sex. ACKNOWLEDGMENTS

These observations were made during a study funded by the Province of British Columbia, Habitat Conservation Trust Fund, Public Conservation Assistance Fund, Wild Bird Trust of British Columbia, James L. Baillie Memorial Fund of Bird Studies Canada, BC Field Ornithologists, and the Municipality of Saanich Parks Dept. I thank John B. Sprague, Ken H. Morgan, and an anonymous reviewer for comments on this manuscript. LITERATURE CITED Bielefeldt, J., R.N. Rosenfield, and J.M. Papp. 1992.

Unfounded assumptions about diet of the Cooper’s Hawk. Condor 94:427-436.

Linduska, J.P. 1943. Cooper’s Hawk carrying a nest of

young goldfinches. Auk 60:597. McCallum, C.A. and S.J. Hannon. 2001. Accipiter

predation of American Redstart nestlings. Condor 103:192-194.

Meng, H. 1959. Food habits of nesting Cooper's Hawks and goshawks in New York and Pennsylvania. Wilson Bulletin 71:169-174.

Nelson, R.W. 1968. Nest-robbing by the Cooper’s Hawk.

Auk 85:696-697. Pietz, P.A. and D.A. Granfors. 2000. Identifying predators

and fates of grassland passerine nests using miniature video cameras. Journal of Wildlife Management 64:71-87.

Rosenfield, R.N. and J. Bielefeldt. 1993. Cooper’s Hawk

(Accipiter cooperii). No. 75 in A. Poole and F. Gill (Editors). The birds of North America. The Academy of Natural Sciences, Philadelphia, Pennsylvania; American Ornithologists’ Union, Washington, D.C.

Sallabanks, R. and F.C. James. 1999. American Robin

(Turdus migratorius). No. 462 in A. Poole and F. Gill (Editors). The birds of North America. The Academy of Natural Sciences, Philadelphia, Pennsylvania; American Ornithologists’ Union, Washington, D.C.

Williams, G.E. and P.B. Wood. 2002. Are traditional

methods of determining nest predators and nest fates reliable? An experiment with Wood Thrushes (Hylocichla mustelina) using miniature video cameras. Auk 119:1126-1132.

Cooper’s Hawk / Bill Heybroek


PURPLE FINCHES FEED ON WILLOW CATKINS

Al Grass 17375 - 27A Avenue Surrey, B.C. V3S 0E9

Abstract -- Two male Purple Finches (Carpodacus purpureus) were seen feeding on willow catkins. Members of this genus, and also sparrows, are known to feed on parts of flowers, but there does not appear to be previous documentation of willow catkins being consumed. Key words: Purple Finches, Carpodacus purpureus, food, feeding habits, willow, Salix, flowers, catkins.

On March 13, 2004, two male Purple Finches (Carpodacus purpureus) were observed feeding on willow catkins (Salix sp.), in the Conservation Area at Maplewood Flats, North Vancouver, B.C. Martin, et.al. (1951) do not list Salix in their analysis of the feeding habits of this species, however, those authors note “…the rosy coloured warbling songsters obtain a large share of their springtime food by eating buds or tree flowers…”. At Maplewood, I have seen Purple Finches feeding on both cherry (Prunus avium) and Pacific crabapple (Malus fusca) flowers.

Flower consumption is a habit shared by other Carpodacus species, as well as sparrows. Both the Spotted Towhee (Papilio maculatus) and Song Sparrow (Melospinza melodia) regularly consume the inner parts (stamens, pistil) of salmonberry (Rubus spectabilis). Petals, and other non-reproductive parts, which apparently have no food value, are not consumed (Jude Grass, Surrey, B.C., personal communication). Nectar consumption is borne out by the fact that Carpodacus finches are regular visitors to hummingbird feeders.

Foraging on willow catkins may not be a rare occurrence, but I could not find it documented in the literature. For willow flowers, it seems reasonable to speculate that staminate flowers, in particular, are consumed for their pollen content (fat and protein). LITERATURE CITED Clements, P. 1999. Finches and sparrows. Princeton

University Press, Princeton, N.J. 500 p. Martin, A, H. Zim and A. Nelson. 1951. American wildlife

plants: a guide to wildlife food habits. Dover Publications, Mineola, N.Y. 473 p.

Purple Finch / Bill Heybroek


APPARENT HYBRID LINCOLN’S X SONG SPARROW AT BOUNDARY LAKE

Chris Charlesworth 725 Richards Road

Kelowna, B.C., V1X 2X5 Abstract -- Accompanied by a second observer, I found an apparent Lincoln’s Sparrow (Melospiza lincolnii) X Song Sparrow (Melospiza melodia) hybrid at Boundary Lake, east of Fort St. John in the Peace River Region of British Columbia. The bird was seen on June 27, 2003, along a gravel oil exploration road on the west side of Boundary Lake. No mention of such a hybrid was found in the literature. Key words: hybrid, sparrows, Lincoln’s Sparrow, Melospiza lincolnii, Song Sparrow, Melospiza melodia, size, plumage.

While birding along a gravel road on the west side of Boundary Lake, east of Fort St. John, Ryan Tomlinson (Kelowna, B.C.) and I were studying sparrows, present in good numbers alongside the road. We had recorded over 6 sparrow species when one bird caught my eye. The bird appeared to be a hybrid Lincoln’s X Song sparrow. It was intermediate in size between the two species and showed plumage traits of both. The facial pattern resembled a Lincoln’s Sparrow more closely than Song, and I noted a buffy malar stripe, gray supercilium and rusty crown. The bird had the “surprised” facial expression associated with Lincoln’s. The breast was similar to that of a typical Song Sparrow, but it was buffier than normal. The bird’s upper parts, including back and wings, were closely matched to that of Song Sparrow. The bird did not vocalize.

Following observation of the sparrow for about 5 minutes at close range both Ryan and I came to the conclusion that it was a hybrid Lincoln’s X Song Sparrow. According to the literature, hybridization of these two species has never been recorded (Beadle & Rising, 2002).

In North America, 31 subspecies of Song Sparrow have been recorded. The subspecies present in northeast British Columbia is M. m. juddi. Two of the three known subspecies of Lincoln’s Sparrow are present in British Columbia, with M. l. lincolnii occurring in the Peace River Region, where they are common breeding birds in shrubby habitats near the forest edge. The Song Sparrow is more of a generalist and will nest in a wide variety of habitats, however it is usually found near water. Cassin’s Vireo / Bill Heybroek

See article on page 6, this issue.

Unfortunately, we did not have a camera to record this bird. Although Lincoln’s Sparrows have not been recorded hybridizing with any other species, Song Sparrows have hybridized with White-crowned Sparrow (Zonotrichia leucophrys) (Pale, 1997). It is not unexpected that these two similar species (Lincoln’s and Song Sparrows) should occasionally hybridize, given that they are closely related and that they nest in similar habitats throughout British Columbia and much of their range. Similarities in plumage between Song and Lincoln’s sparrows makes identification of a hybrid quite difficult. Capturing, documenting and photographing such a bird would be extremely useful in determining the lineage of a hybrid of this type. Perhaps if observers are aware of the possibility of these two species interbreeding there will be further discoveries and the proper documentation can be provided. LITERATURE CITED Beadle, D. and J. Rising. 2002. Sparrows of the United

States and Canada (Photographic guide). Academic Press, London, U.K.

Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M.

Cooper, G.W. Kaiser, A.C. Stewart, M.C.E. McNall. 2001. The birds of British Columbia. Volume IV. University of British Columbia Press, Vancouver, B.C.

Pale, P. 1997. Identification guide to North American birds.

Slate Creek Press, Bolinas, Calif.

volume 13, 2003 british columbia birdsvolume 13, 2003 british columbia birds page 1 contents observ...

Documents