Date: Fri, 7 Feb 2003 11:37:17 -0500
Reply-To: Eran Tomer <etomer@EMORY.EDU>
Sender: Georgia Birders Online <GABO-L@LISTSERV.UGA.EDU>
From: Eran Tomer <etomer@EMORY.EDU>
Subject: Re: Waxwings
In-Reply-To: <002101c2ce8e$a3931b00$6501a8c0@Marion>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Marion,
Many thanks for the data, especially the Georgia-specific figures. Also,
you are right in stating that many factors have to be considered when
looking at CBC and BBS data. Cedar Waxwing is one species that is not
adequately monitored by either survey due to the methodology involved.
This species is gregarious, so spatial data is highly clumped, tough to
chart accurately and is sometimes autocorrelated. Then, Waxwings flocks
are difficult to count with precision and trend data is biased as a result
of flocking behavior. This bird is also nomadic, irruptive in some places,
nests in loose colonies, is somewhat of a food specialist and, in some
settings, can be difficult to hear. All of these bias standard CBC and BBS
methods. That is not to say that waxwing data from these surveys is not
valuable. It does provide a very useful index and a good overview of
geographical occurrence. However, interpreting negative data (lack of
sightings) or population trends can be very tricky here.
Data for the southern Blue Ridge may well end up indicating trouble,
however. Significant population declines have been documented with
reasonable confidence for many forest birds there, including those that
are not neotropical migrants. This is not surprising in light of all the
assaults this region has been sustaining, from development to forest tree
epidemics to air pollution. While most species cannot maintain the same
numbers today as they could 30 years ago as a result, it is fortunate that
few are in imminent danger.
Best regards,
- Eran Tomer
Atlanta, GA
etomer@emory.edu
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