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.