[BCNnet] BCNnet: really interesting ABC study about predators and bird collision victims

[Birdchris at aol.com]

New Study May Help in Reducing Bird Collision Mortality at  Buildings
MEDIA RELEASE
Contact: Robert Johns,  202-234-7181 ext.210, _Email click here_ 
(mailto:bjohns at abcbirds.org)   
  Virginia Opossum by Cody Pope, Wikimedia  Commons 
(Washington, D.C., June 8, 2012) A new study published in the June issue of 
 the Journal of Field Ornithology should prove helpful to  conservationists 
attempting to better understand, quantify, and mitigate one of  the largest 
killers of birds in the world – collisions with glass on  buildings. 
The study, titled: “Scavenging Affects Persistence of Avian Carcasses  
Resulting from Window Collisions in an Urban Landscape,”was produced by Stephen  
B. Hager from Augustana College,IL, Bradley J. Cosentino, from the 
University of  Illinois, and Kelly J. McKay from the BioEco Research and Monitoring 
Center,  IL. 
“One of the more difficult aspects of understanding and ultimately reducing 
 bird collision mortality at the millions of buildings in the U.S. and 
around the  world is accounting for predator scavenging of killed bird 
carcasses. Our study  is the first to show that scavengers remove bird carcasses at 
buildings at  different rates and locations depending on the presence of 
suitable habitat for  predators and if seasonal temperatures allow predators to 
be active. This  information is useful because it can inform researchers 
about where and when  scavengers might be a problem and how to best monitor 
buildings in problem  areas. We also offer advice to researchers about how to 
approach studying  scavengers at buildings in other locations since scavenger 
populations may vary  from region to region,” said Stephen Hager, the study’
s lead researcher. 
“From 300 million up to one billion birds are killed in collisions with  
buildings in the U.S. each year. More accurate measurement of mortality at  
individual buildings leads to a better understanding of causal factors, which  
can lead to better solutions. Carcass persistence studies have typically 
been  conducted along with monitoring of collisions at communication towers 
and in  wind turbine fields. Monitoring of collisions with buildings is more 
difficult  because buildings are numerous, unevenly dispersed and variable in 
size and  design, even in a small town. A few studies have tried to monitor 
representative  samples of buildings but generalizing is difficult and most 
city monitoring  programs focus on documenting the problem and rescuing 
injured birds where  possible. The study by Hager et al is especially 
interesting because it shows  scavengers are able to target areas where carcasses are 
most likely to occur,”  said Dr. Christine Sheppard, Bird Collisions 
Campaign Manager at American Bird  Conservancy. 
The study suggests that (1) times between a bird being killed by a window 
and  being scavenged (carcass persistence) will be shorter at locations with  
preferred habitats for known scavengers, such as raccoons and foxes, and  
predictable sources of food, and (2) knowledge of scavenger distribution and  
activity can be useful in predicting duration of carcass persistence at any 
 given site. Intervals between searches for dead birds at buildings that 
will  minimize the number of carcasses lost to scavengers can then be 
inferred. 
   
Surveillance footage of a raccoon scavenging a  carcass.
Photo by Kelly J. McKay 
The study tested the hypothesis that carcass persistence depends on local  
habitat factors known to influence scavenger behavior. Scavenger activity on 
 bird carcasses was documented at 20 buildings in an urban landscape in  
northwestern Illinois for one week during each season of one year. The study  
also documented species of scavengers and the timing of scavenging using  
motion-triggered cameras. 
The study found that carcass persistence decreased as canopy cover (trees 
and  shrubs within a 50-meter buffer) increased. This is likely because a 
denser  canopy provides more preferred habitat for scavengers. Carcass 
persistence also  decreased as window area on the building increased. This is 
because increase in  window surface increases the number of bird collisions, 
providing a more  predictable source of food for scavengers – a relationship 
scavengers seem to  learn 
On the other hand, carcass persistence increases as pavement cover 
increases,  reflecting diminished preferred habitat for scavengers and consistent 
with a  well-documented hesitancy on the part of some scavengers to attempt to 
gather  readily available prey from paved surfaces. 
The study also looked at carcass persistence as a function of season.  
Researchers monitored 20 bird carcasses in each season. Estimated mean time of  
persistence of carcasses was 82.9 ± 11.7 days for winter and 11.8 ± 7.2 days 
for  other seasons. For example, at one building, carcasses were estimated 
to persist  for an average of 23.7 days in the winter, but just 3.5 days 
during other  seasons. Longer carcass persistence in winter may be explained by 
the diminished  response of raccoons to unpredictable food sources; i.e., 
in winter, mortality  due to window strikes is relatively low, and, as a 
result, scavengers may focus  foraging activities elsewhere. Carcass persistence 
in winter may also be  affected by reduced activity by vertebrate 
scavengers when temperatures are  below freezing. 
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