Date: Wed, 10 Dec 2003 17:14:40 -0500 Reply-To: Maryland Birds & Birding Sender: Maryland Birds & Birding From: Walter Ellison Subject: Re: Migration, genetics and feeders MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Hi Everybody, There are good fairly non-technical discussions of the genetics and learned components of migration in a couple of recent books - "Gatherings of Angels: Migrating birds and their ecology", edited by Ken Able and published by Comstock/Cornell; and Scott Weidensaul's "Living on the Wind: Acoss the hemisphere with migratory birds" published by North Point Press. Both discuss Peter Berthold's findings that pretty much proved that migratory distance and direction in many obligate migratory birds are strongly controlled by genes via Mendelian breeding studies of the Blackcap (a *Sylvia* warbler from Eurasia). When Berthold bred birds with short distance and long distance migration patterns he was able to produce medium distance migrant birds (as measured by period of migratory restlessness in captivity). Similar studies documented a genetic component of migratory direction. This being said, it is also known that many waterfowl and the cranes learn migration routes from social relationships, often in families, but also from mates in succeeding years. A lot of a bird's ability to navigate and determine how to far to migrate appears to be inborn, which can be deduced, as Maurice aptly noted, from the evidence of young birds migrating without much benefit of companionship from experienced birds on their first trips to the wintering grounds. Many young seabirds and shorebirds depart the nesting grounds long after their parents have deserted them. Is migration a simple one-gene phenomenon? Certainly not - it's a complex array of behaviors controlled by lots of genes and experiences. Return trips by young birds and subsequent migrations as adults have a huge learned component in addition to the inborn navigational aids for making the trip. For the most part feeders do not much affect the behavior of long-distance migratory birds such as warblers, hummingbirds, tanagers, or orioles. Although occasional Rose-breasted Grosbeaks and Baltimore Orioles overwinter at feeders in eastern North America the vast majority of their kind continue to journey to the tropics for the winter months. Nonetheless, if increased survival of large numbers of birds could be aided by feeders it's plausible that a population that *already* has a genetic tendency to winter somewhere could be increased by bird feeding (e.g. the foregoing discussions on hummers). A similar situation has also been shown for the Blackcap by Berthold and his students in the case of a recently established and increasing wintering population that migrates from the mainland North Sea coast to southern Britain where new plantings and warming climate have made it possible for them to survive the northern winter. Several birds appear to employ both a short distance and long distance migration strategy - Gray Catbirds regularly winter all along the eastern seaboard in small, but not insignificant numbers, while most others go to the tropics. Feeders also can affect migrants such as finches and raptors that rely on lack of food to influence their urge to move on. For instance, declines in migration counts of Sharp-shinned Hawks have coincided with huge increases of sharp-shins on CBCs in the Northeast. What could hold Sharpies up North? How about flocks of juncos and House Finches at northern feeding stations? Good Birding, Walter Ellison 23460 Clarissa Road Chestertown, MD 21620 phone: 410-778-9568 e-mail: rossgull@crosslink.net "A person who is looking for something doesn't travel very fast" - E. B. White (in "Stuart Little") ----- Original Message ----- From: "Maurice Barnhill" To: Sent: Wednesday, December 10, 2003 10:02 AM Subject: Re: [MDOSPREY] Human intervention > Gerald & Laura Tarbell wrote: > > >All points taken with interest. However, wasn't some of the research > >that Lorenz and others did with geese evidence that migration is > >learned behavior, possibly not genetic, as you claim? If it is > >learned, then it might even be possible to teach them to fly north > >for the winter. Of course, > >they might starve as a result, but the point I am making is that your > >genetic origin seems to be more assumed than proven. Any other > >thoughts out > >there on this? > > Jerry > > > > > Geese migrate in family groups, so it is possible that some or even > all migration behavior is learned. However, in many and probably most > species the young migrate separately from the adults, so it is hard to > see how their behavior could be learned. > > I agree that my comments do not apply to geese and that there may be > other species whose migratory behavior is learned. > > -- > Maurice Barnhill ======================================================================= To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com with the following message in line 1: signoff mdosprey ======================================================================= =========================================================================