[CT Birds] Mocking bird numbers
eric_r_larson at hotmail.com
Wed Mar 28 09:54:04 EDT 2012
Chris points out several good reasons for the surge in mockingbird numbers in the Northeast, but the recent trend towards decline may not be solely due to environmental changes, but just a simple phase of a predator-prey cycle ( for a good overview - http://www.nature.com/scitable/knowledge/library/dynamics-of-predation-13229468) where the predators are on the rise. As the numbers of mockingbirds increased, they may have fallen prey to and increased success of predators (cats, feral and house associated, predatory hawks, and other nest-raiding species, e.g. crows, raccoons ). Also, a decline in competitors for their niche may have contributed to the rise, and return of the competitors (e.g,. other songbirds that also feed on multiflora rose hips) may contribute to the cycle.
In the end, who knows?
Date: Wed, 28 Mar 2012 04:42:12 -0700 (PDT)
From: Chris Elphick <elphick at sbcglobal.net>
To: ctbirds at lists.ctbirding.org
Subject: [CT Birds] mockingbird follow-up
Message-ID: <1332934932.86440.YahooMailRC at web81304.mail.mud.yahoo.com>
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Carol asked about reasons for the changing mockingbird numbers. I have not done
a careful search of the literature, but the general dogma is that the initial
increase was due to a combination of suburbanization (which brings in
berry-producing shrubs and may have other advantages for birds that will settle
there - e.g., reduced nest predation rates), a warming climate that has allowed
northward expansion of numerous species, and the spread of the invasive
multiflora rose. I think there is at least one study that makes a strong case
for the importance of the latter, but don't recall the details.
I've not seen anyone address the more recent decline, but my hypothesis would be
that it is likely related to the loss of early successional habitat - open
fields with scattered bushes are increasingly turning into young forest or
(probably more likely, especially in more recent times) being developed. One
way to test these ideas would be to look back at habitat change in the vicinity
of BBS points and see if changes occur where/when numbers decline.
If others shared Roy's question about the "1966" date, it simply indicates that
the gray line represents the population level in 1966 when the survey began.
The slow load and lack of explanation on the graph itself are things that will
be fixed once the web site is completed.
elphick at sbcglobal.net
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