http://www3.interscience.wiley.com/cgi-bin/fulltext/119881756/HTMLSTART
Bird migration times, climate change, and changing population sizes
Global Change Biology Volume 14, Issue 9, Pages 1959-1972
Published Online: 28 Jun 2008
Abstract
Past studies of bird migration times have shown great variation in
migratory responses to climate change. We used 33 years of bird
capture data (1970–2002) from Manomet, Massachusetts to examine
variation in spring migration times for 32 species of North American
passerines. We found that changes in first arrival dates – the unit of
observation used in most studies of bird migration times – often
differ dramatically from changes in the mean arrival date of the
migration cohort as a whole. In our study, the earliest recorded
springtime arrival date for each species occurred 0.20 days later each
decade. In contrast, the mean arrival dates for birds of each species
occurred 0.78 days earlier each decade. The difference in the two
trends was largely explained by declining migration cohort sizes, a
factor not examined in many previous studies. We found that changes in
migration cohort or population sizes may account for a substantial
amount of the variation in previously documented changes in migration
times. After controlling for changes in migration cohort size, we
found that climate variables, migration distance, and date of
migration explained portions of the variation in migratory changes
over time. In particular, short-distance migrants appeared to respond
to changes in temperature, while mid-distance migrants responded
particularly strongly to changes in the Southern Oscillation Index.
The migration times of long-distance migrants tended not to change
over time. Our findings suggest that previously reported changes in
migration times may need to be reinterpreted to incorporate changes in
migration cohort sizes.
http://www.sciencemag.org/cgi/content/full/321/5892/1051
A Matter of Timing
Bruce E. Lyon,1 Alexis S. Chaine,2 David W. Winkler3
Science 22 August 2008: Vol. 321. no. 5892, pp. 1051 – 1052
Climate change is causing shifts in the distribution and phenology of
many plants and animals (1, 2). Birds have played a key role in
detecting these changes, because long-term data are available on the
distribution, migration, and breeding of many species. Studies of the
timing of egg laying--a key trait with extensive records dating back
half a century for some species--are providing crucial insights into
the mechanisms that underlie the response to climate
change.==============================www.birding-aus.org
birding-aus.blogspot.com
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