Date: 3/1/17 8:09 am
From: Johnson, Erik <ejohnson...>
Subject: Re: [LABIRD-L] LABIRD-L Digest - 27 Feb 2017 to 28 Feb 2017 (#2017-54)
The CBC database lists 742 Red-tailed Hawks (!) for Crowley during the 89th CBC (winter 1988-1989), which is the first year that Crowley was run/entered. Since then, Crowley ranged from 267 to 573 between the 90th and 102nd CBC. It hasn't topped 100 birds since the 113rd CBC, and hit a record low of 53 in the 116th CBC (although 105th CBC reported a record low when considering effort, of 0.39 birds/hr).

But looking across all other LA CBCs, the dramatic decline (by an order of magnitude) on the Crowley CBC appears to be an exception, and in discussions with Van off-list, this may had something to the quality of effort in the early days having been quite exceptional. Red-tailed Hawks across other LA CBCs mostly appear to have held steady or even increased slightly. I'm not sure how to reconcile this with the recent Condor paper, except that it may have to do with the selection of counts used, the time periods considered, or how effort is used as a correction to raw bird counts. As with anything, the devil is in the details, and I hope to dig into this more deeply.

Erik Johnson
S Lafayette, LA
Ejohnson AT Audubon.org



-----Original Message-----
From: Bulletin Board for Dissemination of Information on Louisiana Birds [mailto:<LABIRD-L...>] On Behalf Of Progne99
Sent: Wednesday, March 1, 2017 9:14 AM
To: <LABIRD-L...>
Subject: Re: [LABIRD-L] LABIRD-L Digest - 27 Feb 2017 to 28 Feb 2017 (#2017-54)

I remember that the first or second year of Crowley CBC we led the nation in Red-tails.


Sent via the Samsung Galaxy S®6 active, an AT&T 4G LTE smartphone
-------- Original message --------From: LABIRD-L automatic digest system <LISTSERV...> Date: 3/1/17 12:00 AM (GMT-06:00) To: <LABIRD-L...> Subject: LABIRD-L Digest - 27 Feb 2017 to 28 Feb 2017 (#2017-54) There is 1 message totaling 75 lines in this issue.

Topics of the day:

  1. LALIT: Declining winter populations of Red-tailed Hawks

----------------------------------------------------------------------

Date:    Tue, 28 Feb 2017 22:44:20 +0000
From:    James V Remsen <najames...>
Subject: 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>

------------------------------

End of LABIRD-L Digest - 27 Feb 2017 to 28 Feb 2017 (#2017-54)
**************************************************************
 
Join us on Facebook!