Greetings All

Sorry that my response here is quick.
Wayne, I would suggest going to the SORA website, choose any ornithological journal, and search for molt migration.


Or, you could look at the Birds of North America accounts for
Bullock's Oriole
BH Grosbeak
Western Tanager
Painted Bunting (or read my North American Birds article, written with Robb Hamilton, on Painted B vagrancy)
Warbling Vireo
Dusky Flyatcher

for starters.


I think my original post detailed the reason for a molt migration in western North American passerines quite sufficiently, so rather than repeat myself, Wayne, you might want to re-read the original post.

Steven Mlodinow
Everett WA

-----Original Message-----
From: Wayne Weber <contopus at telus.net>
To: TWEETERS <tweeters at u.washington.edu>
Cc: STEVE MLODINOW <sgmlod at aol.com>; CHARLIE WRIGHT <c.wright7 at comcast.net>
Sent: Fri, 8 Aug 2008 11:08 am
Subject: Migration versus post-breeding dispersal




Charlie, Steve, and Tweeters,

?

I wasn?t trying to say that no passerines ever begin southward migration in late July. In the case of some individuals, and some species, they may do so. I would have to agree with Charlie that birds heard overhead at night are almost certainly engaged in migration rather than post-breeding dispersal. However, in my experience, in the Pacific Northwest, the vast majority of passerine movements in late July and for at least the first 10 days of August appear to be short-distance post-breeding dispersal rather than long-distance migration. However, it may be hard to
tell the difference unless you are dealing with banded birds or birds with radio transmitters, so that you can tell exactly how far they moved.

?

I?m intrigued by Steve?s comments about molt migration. Molt migration is well-documented in waterfowl and in some other non-passerines, but I was unaware that it had been documented in passerines. Steve, can you cite any published papers that document this phenomenon in passerines?

It?s easy to explain molt migration in waterfowl, which lose many of their flight feathers at once and are often flightless for 2-3 weeks during the summer, but I find it harder to understand why this should happen in passerines, which molt more gradually and generally don?t have a flightless period.

?

I agree that Bullock?s Orioles and Black-headed Grosbeaks leave quite early (in BC, most orioles are gone by August 31, and grosbeaks by at least September 7), but I thought this was just ordinary fall migration, not a molt migration.

?

Terminology is important, and part of people?s differing perceptions may be a matter of semantics.

In the dictionary sense, almost any movement of birds could be considered to be ?migration?. However, in ornithological parlance, migration is usually considered to be a regular, twice-a-year movement between a breeding area and a wintering area which is often hundreds or thousands of miles away.

?

The point I was really trying to make is that a lot of what casual observers?
and some experienced observers?refer to as ?migration? is not migration in this second, more usual, sense, but is really post-breeding dispersal. Every year, in July and early August, there is a flurry of messages on TWEETERS and other birding groups about bird species that popped up in the backyard that the observer hadn?t seen there since May, with the assumption that it must be, or could be, migration.

The fact that these same species may breed less than 2 miles from the observer?s backyard is ignored, or in some cases, perhaps unknown to the observer. An example is Kristi Hein?s message about Golden-crowned Kinglets in Anacortes. I?ve done lots of birding year-round on Fidalgo Island, and I can assure Kristi and other observers that G.C. Kinglets breed commonly there, even if they are somewhat commoner in winter. Golden-crowned Kinglets are a good example of a species which is a ?partial migrant?, with a breeding range that broadly overlaps its winter range. The Puget Sound area is in the overlap zone, such that Golden-crowns are found commonly here in conifer forest all year.

?

True migration (breeding area vs. wintering area) and post-breeding dispersal are distinct phenomena (the first is mediated by hormones, the second appears not to be), although they can be hard to tell apart in late summer.

?

Wayne C. Weber

Delta, BC

contopus at telus.net

?

?

?


From: tweeters-bounces at mailman2.u.washington.edu [mailto:tweeters-bounces at ma
ilman2.u.washington.edu] On Behalf Of sgmlod at aol.com
Sent: August-06-08 11:20 AM
To: Tweeters at u.washington.edu
Subject: [Tweeters] migration


?

Greetings All

Wish I knew more about this topic.

First of all, true passerine migration begins in July for many western species and some eastern species. BH Grosbeaks, Western Tans, Cassin's Kingbirds start to appear in Baja's Cape and in Sonora in July, and these locations are quite distant from their breeding grounds.

This is because many western passerines engage in a molt migration. They leave the (usually) very arid (in July/August) Cascades and Sierras and head for the sw US and nw Mexico, where monsoon rains are usually going on and insect life is abundant. Clearly some members of these species linger, but it is amazing how few BH Grosbeaks and Bullock's Orioles we see after 1 September, or even 15 August.

After molting at these locations, many "molt migrants" continue on to their wintering grounds.

In the east, most species molt before southbound migration, and then do not pause for any extended period of time until they reach their non-breeding/wintering/resting grounds. Admittedly, their southbound migration is more leisurely than their northbound migration, but I bet birds rarely spend more than a week at a given stopover.

Some western migrants do the same.

One of the differences between Bullock's and Baltimore Orioles, and between eastern and western Warbling Vireos, is that the eastern equivalent molts on breeding grounds, and?the western versions head
south first.

So, a migrant Warbling Vireo in mid-July would not be surprising in the west.

As for "post-breeding dispersal".
I am nearly totally ignorant as to how much this occurs in passerines. Certainly, sagebrush sparrows flock up and move about a bit.... but how much is a bit? Don't know. A couple miles? Dozens of miles? Random direction?

I've not seen something among woodland passerines that really matches what one sees in sagebrush sparrows. My neighborhood does not fill up with flocks of wandering Wilson's Warblers for a month before they depart as one might find with Brewer's Sparrows in e. Washington. In June, and to a lesser extent in early July, I do encounter wandering individuals, not in great numbers, that I suspect represent birds that failed to find mates or had their nests failed. Many of these birds are singing males that hang around for a day or two then disappear.

So, what do Wilson's Warblers (not molt migrants, I believe) do after their young are independent? I have no idea. Do they start south? Do they disperse (which implies a somewhat random direction) before migrating? If so, how far do they disperse? Perhaps they move up into the mountains and flock up there before heading south.

There may well be someone out there reading this listserv that knows, or a peak at the Birds of North America accounts for some of these species may provide insight.

And I see no reason why dispersal would be diurnal vs. nocturnal.....

Blah, blah, blah, blah, blah

Signi
ng out
Steven Mlodinow
Everett WA


.