Date: 2/28/17 2:59 pm
From: James V Remsen <najames...>
Subject: [LABIRD-L] LALIT: Declining winter populations of Red-tailed Hawks
LABIRD: Those of you with several decades of experience have certainly noticed that our wintering populations of Red-tailed Hawks in south Louisiana nowadays are dramatically lower than they once were. Up into the early 90s at least, one could easily see 100+ Red-tailed Hawks in a day in the rice country of SW LA. Back in that era, on a good fall day at my house, I could see 10+ migrating Red-tails high overhead headed S after a cold front; nowadays I see maybe 1-2 likely migrants in an entire fall. The Baton Rouge CBC currently gets only about 1/3 as many Red-tails/party-hr as it did in the 70s-80s.

The latest Ornithological Applications (=Condor) has a paper that quantifies this trend using hawk-watch counts and CBC data from North America as a whole. The take-home message is that breeding populations are evidently steady or increasing (as they are in south Louisiana) but the tendency to remain farther north (undoubtedly because of climate change) is causing the decline of wintering populations in the south. (Contact the corresponding author if you want a pdf of the full paper):

Combining migration and wintering counts to enhance understanding
of population change in a generalist raptor species, the North American
Red-tailed Hawk

Neil Paprocki,1* Dave Oleyar,1 David Brandes,2 Laurie Goodrich,3 Tara Crewe,4 and Stephen W. Hoffman5

1 HawkWatch International, Salt Lake City, Utah, USA
2 Department of Civil and Environmental Engineering, Lafayette College, Easton, Pennsylvania, USA
3 Hawk Mountain Sanctuary, Orwigsburg, Pennsylvania, USA
4 Bird Studies Canada, Port Rowan, Ontario, Canada
5 Montana Audubon, Helena, Montana, USA
* Corresponding author: npaprocki at hawkwatch.org<http://hawkwatch.org>

ABSTRACT
An increasing body of scientific evidence supports the idea that many avian species are changing their migratory
behavior as a result of climate change, land-use change, or both. We assessed Red-tailed Hawk (Buteo jamaicensis)
population trends in 2 parts of the annual cycle (fall migration and winter) to better understand regional population
trends and their relationship to changes in migration. We conducted 10 yr, 20 yr, and 30 yr trend analyses using
pan–North American standardized fall migration counts and Christmas Bird Counts. We quantitatively compared
trends in seasonal counts by latitude within the eastern and western migratory flyways. Our combined analysis of
migration and wintering count data revealed flyway-specific patterns in count trends suggesting that Red-tailed
Hawks are undergoing substantial changes in both migratory behavior and population size. Decreasing Red-tailed
Hawk wintering and migration counts in southern regions and increasing winter counts in northern regions were
consistent with other observations indicating changes in migratory strategy; an increasing number of Red-tailed
Hawks do not migrate, or migrate shorter distances than they did in the past. Further, Red-tailed Hawk populations
have been stable or increasing across much of North America. However, we found strong negative count trends at
the northernmost migration sites on the eastern flyway, suggesting possible breeding-population declines in the
central and eastern Canadian provinces. Our findings demonstrate the benefit of using appropriate data from
multiple seasons of the annual cycle to provide insight into shifting avian migration strategies and population
change.


=================

Dr. J. V. Remsen
Prof. of Natural Science and Curator of Birds
Museum of Natural Science/Dept. Biological Sciences
LSU, Baton Rouge, LA 70803
najames<at>LSU.edu<http://lsu.edu>

 
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