FYI -
-----Forwarded Message-----
>From: Scott Weidensaul <>
>Sent: Sep 17, 2007 10:58 AM
>To:
>Subject: [PABIRDS] Mute swan impacts
>
> On a number of occasions on this list, we've discussed mute swans
>and their potential impact on the environment, most recently when the
>PGC began implementing a management plan that calls for no feral mute
>swans, and only 250 legally held captive birds, statewide.
>
> Similar plans in other states, especially Maryland, were held up by
>lengthy court fights by animal-rights groups, and have created a
>great deal of public controversy. In a nutshell, swan defenders
>argued that there was no evidence that the swans were, as claimed,
>detrimental to native species, especially aquatic ecosystems.
>
> Now, however, a major study of the impact of mute swans on
>submerged aquatic vegetation (SAV) in the Chesapeake Bay has
>documented that the birds are indeed having a profound effect on the
>bay's beleaguered SAVs, the foundation for much of this estuary's
>ecology.
>
> The paper, "Mute Swans' impact on submerged aquatic vegetation in
>Chesapeake Bay," (K. S. Tatu, J. T. Anderson, L. J. Hindman, and G.
>Seidel. 2007. Journal of Wildlife Management 71:1431-1440) found that
>areas in Maryland grazed by swans had up to 80 percent less SAV cover
>than those from which swans (but not other SAV predators, like
>cow-nosed rays) were excluded. The authors also found that big flocks
>of young and nonbreeding swans could almost entirely eliminate SAV
>beds in spring and summer, a period when few waterfowl were
>traditionally grazing on SAVs in the Chesapeake.
>
> Since one of the study site is the Eastern Shore Audubon sanctuary
>my wife used to manage, this all hits home for us, and reinforces
>what we already suspected about swan impacts. The study is very
>strong vindication for the controversial -- but necessary -- program
>to remove mute swans from the wild in the East and Midwest. Given
>that Maryland's mute swan population jumped from five in 1962 to more
>than 4,000 in 1999, it's critical that states like Pennsylvania,
>where swan populations are still relatively low, move quickly to
>prevent similar problems.
>
> Scott Weidensaul
> Schuylkill Haven, PA
>
> P.S. I have a pdf of the journal article, and will be happy to
>email to anyone if they contact me privately. |