Precipitation Effects on Winter Bird Species Utilizing Christmas Bird Counts
Isaac Morgan, Elizabeth Tanner, Jeff Monroe, Jason Behrends
University of Wisconsin- Platteville Biology Department
Introduction
•
•
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.
Methods
• 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.
Results
CBC Snow Cover Data
Correlation
Coefficient
-0.155
2.5
Individuals/hour
Species
2
European
1.5
Starling
American
0.311
1
Robin
0.5
Black-capped 0.285
Chickadee
0
American
0.103
0
5
10
15
Crow
CBC Snow Cover (in)
Horned Lark
-0.010
Figure 1: Correlation between American Robin and
Great Horned 0.225
yearly precipitation totals. (r= .311)
Owl
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
Yearly Precipitation Totals
Species
Correlation
Coefficient
European
Starling
American
Robin
Black-capped
Chickadee
American
Crow
Horned Lark
-0.007
0.459
0.218
0.079
2.5
Individuals/ hour
• 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 19772011 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:
Conclusions
2
1.5
1
References
0.5
•
0
20
0.076
• 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.
30
40
Yearly Precipitation Level (in)
Great Horned 0.161
Figure 2: Correlation between American Robin and
Owl
yearly precipitation totals. (r= .459)
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.
50
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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.