Precipitation Effects on Winter Bird Species Utilizing Christmas Bird CountsIsaac Morgan, Elizabeth Tanner, Jeff Monroe, Jason Behrends

University of Wisconsin- Platteville Biology Department

Introduction

Methods

Results Conclusions

References • Used Riveredge CBC data from 1977 to 2011 on European Starling, American Robin, American Crow, Horned Lark, Great Horned Owl and Black-Capped Chickadee and compared it to both CBC snow cover data and NOAA yearly precipitation data to see if winter population of these birds is negatively or positively affected by the previous summer precipitation levels and current winter levels. Regression tests were used to determine significance.

• Each bird species count was standardized by dividing each count by the number of party hours (Butcher et al 1990).

• These birds were chosen because they are found in the area both in the summer and winter. Also the wide variety of bird types may give us insight into which kinds of birds are affected by the precipitation levels.

• Only one of our bird species, the American robin, had a significant correlation with yearly precipitation data and CBC snow cover data.

• As yearly precipitation levels increased, so did the likelihood of seeing the American Robin during the CBC (r= .459).

• The same is true for snow cover, the more snow cover during the CBC, the more likelihood of see the American Robin, however this correlation is weak (r= .311).

• An explanation for why American robins are affected by yearly precipitation could be because more rainfall may lead to more production of seeds which is an important food source for robins (Howe et al 1982).

• Another explanation could be that more moisture brings out a greater abundance of grubs and earthworms, another important food source for American robins (Duriez et al 2006).

• A possible explanation for our significant results could be the result of the low population density of American Robins. Robins are migratory birds and are rarely seen in the winter. This could cause a discrepancy in the data. Any trend may be over exaggerated due to the low numbers of birds seen during the CBC count.

• Several suggestions for further research…• Test the effect of summer precipitation on the same

species.• Test yearly precipitation and CBC snow cover on

other species of birds.

• The Christmas Bird Count (CBC) takes place annually since 1900. For our study we used data from the Riveredge Nature Center located in southeastern Wisconsin. This location has been recording data since 1969.

• Participants in this program record weather conditions, numbers of birds observed of each species within a 15 mi diameter. It takes place on one day between December 14 and January 5.

• Also recorded are number of parties and observers, whether each bird was observed in the field or at a feeder, and number of hours spent observing the birds

• For our study we used Riveredge CBC data from 1977-2011 and yearly precipitation data by National Oceanic and Atmospheric Administration (NOAA).

• We observed the relationship between yearly precipitation totals and the number of birds seen per party hour for the European Starling (Sturnus vulgaris), American Robin (Turdus migratorius), Black-capped Chickadee (Poecile atricapillus) , American Crow (Corvus brachyrhynchos), Horned Lark (Eremophila alpestris), and Great Horned Owl (Bubo virginianus).

• Our hypotheses are:• Yearly precipitation data would have a positive

correlation with each of the species.• CBC snow cover data would have a negative

correlation with each of the species.

Species Correlation Coefficient

European Starling

-0.155

American Robin

0.311

Black-capped Chickadee

0.285

American Crow

0.103

Horned Lark -0.010Great Horned Owl

0.225

CBC Snow Cover Data

Table 1: Correlation coefficient values of a correlation test between individuals/hour and CBC snow cover data. Only significant correlation is a low positive correlation with the American Robin

0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

CBC Snow Cover (in)

Indi

vidu

als/

hour

Species Correlation Coefficient

European Starling

-0.007

American Robin

0.459

Black-capped Chickadee

0.218

American Crow

0.079

Horned Lark 0.076Great Horned Owl

0.161

Yearly Precipitation Totals

Table 2: Correlation coefficient values of a correlation test between individuals/hour and yearly precipitation levels. Only significant correlation is a moderate positive correlation with the American Robin.

20 25 30 35 40 450

0.5

1

1.5

2

2.5

Yearly Precipitation Level (in)

Indi

vidu

als/

hou

r

Figure 2: Correlation between American Robin and yearly precipitation totals. (r= .459)

Figure 1: Correlation between American Robin and yearly precipitation totals. (r= .311)

• Butcher, G. S., Fuller, M. R., McAllister, L. S., & Geissler, P. H. (1990). An Evaluation of the Christmas Bird Count for Monitoring Population Trends of Selected Species. Wildlife Society Bulletin, 18(2), 129-134.

• Daily Hydrometeorological Products. (n.d.). Retrieved from National Weather Service website: http://forecast.weather.gov/product.php?site=MKX&product=HYD&issuedby=MKX

• Duriez, O., Ferrand, Y., & Binet, F. (2006). An Adapted Method for Sampling Earthworms at Night in Wildlife Studies. The Journal of Wildlife Management, 70(3), 852-858.

• Robin Photo: www.themississagilighthouse.com• Black-capped Chickadee Photo: www.hdwallpapersfan.com

Acknowledgements We would like to acknowledge past contributors to the Riveredge Nature Center CBC.