Date: Wed, 10 Dec 2003 20:49:08 -0500 Reply-To: Maryland Birds & Birding Sender: Maryland Birds & Birding From: Gail Mackiernan Subject: Re: Migration, genetics and feeders In-Reply-To: <009301c3bf6b$0231f460$b9a1c7cf@mdatlasxz1p6g> Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Oops, sorry about that -- hit the wrong button! What I was going to say is that an addendum to the Sylvia warbler story is that in some species the part of the population which migrated furthest showed severe declines in the late 1960s due to unfavorable wintering conditions in Africa, whereas the birds wintering in western Europe did better. The increasing number of birds wintering in western Europe may reflect not only warmer more favorable conditions in these regions, but also dryer, less favorable conditions in traditional wintering areas. We may be seeing a genetic tendency to migrate west and short in the process of being selected for. Gail Mackiernan on 12/10/2003 5:14 PM, Walter Ellison at rossgull@CROSSLINK.NET wrote: > 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") > > ======================================================================= To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com with the following message in line 1: signoff mdosprey ======================================================================= =========================================================================