Poised for Flight: Trinity/Six Rivers Natl. Forest

This week we visited the Trinity River sites. It is hard to believe it but breeding season is nearly over. Birds are definitely on the move, and singing has nearly stopped. We are capturing many molting birds.Juveniles are initiating their pre-formative molt (to replace lower quality juvenal body feathers but not flight feathers) and many adults are beginning their adult pre-basic molts (a yearly replacement of all body and flight feathers). It is interesting to catch birds in this molting process because you can get a feel for the sequence that feathers are molted. It also allow us to actually see the molt limits we have been using all season to age birds being created. A quick molt refresher:

I keep it straight this way. All North American songbirds replace all feathers once a year after breeding and this molt is called the prebasic molt. Some birds then have inserted molts within these yearly cycles. All juveniles have an inserted molt called a preformative whose job is to replace low quality juvenal feathers. This is not a complete molt and in most species does not include flight feathers. Some birds also have an inserted molt called an alternate molt which yields feathers we often associate with breeding plumage. These are also not complete molts and generally do not include flight feathers. Note that the yearly molt cycles are not interrupted by the inserted molts. All birds still molt all their feathers after breeding.

In this Yellow Warbler, the inner wing coverts are being replaced in the pre-formative molt. The molt limit is being created between the carpal covert and the alula in a pattern typical of warblers.

Yellow-breasted chat is the exception within the warbler family and often undergoes an eccentric pre-formative molt, that is it often replaces some of its outer primaries as seen in this photo. (Remember preformative molts in most North American passerines do not include flight feathers)

Another thing to consider is that we have to start being careful aging birds because we can no longer assume that the presence of a molt limit indicates a second year bird. It could be a juvenile that has gone through it's pre-formative molt, or an adult that has not yet initiated its adult prebasic molt. Feather wear can help us in aging these birds however, the way we can most accurately age these birds is by skulling it. This molt stuff can be a bit confusing and for anyone who is interested in learning more I highly recommend reading the introduction to Peter Pyle's bird identification book used by banders to age and sex birds. Beware that molt theory has been slightly modified recently and Part I of Pyle's book uses old terminology while Part II has been updated and includes new terminology.

Ok enough of that,
Highlights this week were good looks at a ruffed grouse, a California Quail in the net, and 7 species of warbler banded at Indian Valley.

Birds Banded:
Hamilton Ponds 7/21
Lesser Goldfinch 1
Orange-crowned Warbler 3
Macgillivray's Warbler 1
Yellow-breasted Chat 1
Pacific Slope Flycatcher 1
Anna's Hummingbird 1
Spotted Towhee 1
Wilson's Warbler 1
Swainson's Thrush 1

Indian Valley 7/22
Hermit Warlber 7
Yellow Warbler 5
Orange-crowned Warbler 1
Macgillivray's Warbler 1
Wilson's Warbler 1
Black-throated Grey Warbler 1
Audubon's Warbler 1
Cassin's Vireo 5
Mountain Chickadee 1
Purple Finch 3
Red-breasted Sapsucker 1
Spotted Towhee 2
Dusky Flycatchers 15
Anna's Hummingbird 2
Golden-Crowned Kinglet 2

Stiener Flat 7/23
Yellow-breasted Chat 2
Song Sparrow 2
Black-headed Grosbeak 1
Spotted Towhee 2
Pacific Slope Flycatcher 1

Hocker Flat 7/24
Macgillivray's Warbler 2
Song Sparrow 3
Yellow-breasted Chat 3
Wrentit 1
Bushtit 2
Western Tanager 5
Spotted Towhee 7
Red-breasted Sapsucker 1
Black-headed Grosbeak 8
Pacific Slope Flycatcher 1
California Quail 1

Photos...Enjoy!!

An adult male Black-headed Grosbeak captured at Steiner Flat, CA

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A hatch year (HY) Pacific Slope Flycatcher at Hamilton Ponds, CA

A Wilson's Warbler captured at Hamilton Ponds, CA. Any guidebook will tell you this is a male bird based upon the black crown patch however, this bird is a female!! (Brood patch present) The females of the pacific population seem to have extensive black on the head.