I thought I'd help you guys out with this molt thing. I think that some
clarification may help in the understanding of bird molts. It might help
others as well.

The juvenile Vireos (and a majority of other birds) have a partial prebasic
molt, which is the molt before entering the winter plumage (basic plumage).
In Hatch Year birds (HY), prebasic molt is partial while being complete in
all other ages, After Hatch Year/After Second Year birds (AHY/ASY) (see
terms below). The prealternate molt is the molt that the bird has before
the establishment of its breeding plumage. It is present in some of the
Vireos in early spring (BCVI, GRVI, SOVI, and YTVI).

Partial molt: molt of the lesser, medial and greater coverts and body
feathers

Incomplete molt: all body, all coverts and some flight feathers (primaries,
secondaries, retrecies)

Complete molt: All feathers on the bird

The process of a partial prebasic molt of HY's in the Vireos (and a
majority of other birds) consists of a molt of the lesser, medial and
greater coverts. Once the lessers are half molted the medial coverts
begin. Once they are half molted the the Greater coverts begin, and once
they are half molted the allula and carpal feathers also molt. Some of the
Vireos loose there tertials and secondaries as well in a prealternate and
prebasic molt. These are timed with the loss of the greater coverts. Once
they are about half molted they will loose some of there secondaries,
retrecies and perhaps some of the primaries. It is true that the REVI
(red-eyed vireo) molts its feathers during migration. Right now I am
catching several of them and notice that they are in the mid to latter
stages of PB molt, both HY and AHY/ASY birds.

I hope that this information clears up the confusion of molting terms and
types.
The molt of vireos and others can be quite complex. Much study is still
needed to understand the true aspect of passerine molts.

Libor

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From: CHRISTINE W. MAACK <73201.3124 at compuserve.com>
To: Tweetlist <tweeters at u.washington.edu>
Subject: Vireo molt chronology
Date: September 5, 1997 4:04 PM

In case you don't have access to the banders' manual
(Pyle et al: Identification Guide to North American
Passerines), here is what it says about Red-eyed Vireo:

Molt - PB (Prebasic): HY partial-incomplete (Jul-Sep),
AHY incomplete-complete (Jul-Oct); PA (Prealternate):
SY absent? ASY absent-incomplete (Feb-Apr). 1st PB
occurs on the summer grounds and sometimes includes
the terts. In some (possibly all) AHYs the PB appears
to be suspended over migration, with some flight
feathers not renewed until the PA. This should be
further investigated.

That sure clears that up, doesn't it?

Chris Maack
Anchorage, AK
CMaack at compuserve.com
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