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Posts tagged “Spinus tristis

American Goldfinch Plumage Anomaly

Molting, the replacement of all or some of a bird’s feathers, occurs in response to a mixture of hormonal changes brought about by seasonal changes. This process serves to replace worn feathers (they cannot repair themselves) and can play a part in seasonal camouflage as well as attracting a mate.

All of our small songbirds have a complete molt, replacing all of their feathers in late summer. In addition, many species have a partial molt (replacing body feathers but not wing or tail feathers) in the spring.

According to David Sibley, American Goldfinches begin to molt all of their (alternate/breeding plumage) feathers in September, with the males replacing their brilliant gold feathers with much duller feathers by November.  Come spring and the breeding season, male goldfinches replace their dull (basic/non-breeding) body feathers (but not the wing or tail feathers) with new, bright feathers.

Imagine my surprise when I spied a brilliantly colored American Goldfinch at my feeder this week.  According to ornithologist George Clark, it’s usually March before one starts to see an American Goldfinch in breeding plumage. One can only wonder what prevented this individual from molting its breeding plumage in the fall. (Photo: male American Goldfinch, winter plumage; inset – male American Goldfinch in breeding plumage in January)

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American Goldfinches Dining On Thistle Seeds

A. goldfinch and thistle seed_U1A8258

American Goldfinches are almost exclusively granivorous (consumers of seeds/grains).  Very few insects are consumed by these birds, even when feeding nestlings.  This is highly unusual in that spiders and insects are an essential part of 96% of N.A. terrestrial bird species. At the very least, most seed-eating birds feed their nestlings insects. (Brown-headed Cowbirds lay their eggs in other birds’ nests, leaving the raising of their young up to the host bird. It is rare that a cowbird chick will survive to leave an American Goldfinch nest, probably because it cannot thrive on a diet of virtually all seeds.)

The seeds of plants in the Composite family (sunflowers, thistles, dandelions, etc.) are the preferred food of goldfinches. Thistle seeds, being high in fat and protein, are high on the list. There appears to be a correlation between the late nesting period of goldfinches (late June or early July) and the flowering of thistles.  By the time American Goldfinch eggs have hatched, there is an ample supply of thistle seed for the nestlings.

Now is the time to keep an eye on the seedheads of thistles, dandelions and other composites for the acrobatic seed-plucking antics of American Goldfinches.

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Why You See Birds On Dirt Roads

1-5-17 goldfinches in road 049A1683There are two parts to a bird’s stomach, each of which has a different function. The proventriculus, or glandular stomach, secretes enzymes that begin the digestive process. Lacking teeth, birds also have a gizzard, or muscular stomach, that grinds up the food that a bird has eaten. For this reason, the gizzard is usually very strong and muscular. Seed-eating birds often eat seeds whole and need to break them into tiny pieces in order to digest them. Many of these birds can be seen on dirt roads, picking up small stones and grit which then collects in their gizzards and helps pulverize the food they’ve eaten.  (Photo:  American Goldfinches)

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Male American Goldfinch’s Seasonal Plumage

3-17-15  male American goldfinch IMG_0482Most songbirds have one complete molt every year, in the late summer. Some, like the American goldfinch, have another (partial) molt in the spring. Last fall male goldfinches molted, replacing many of their bright yellow feathers with drab, greenish-gray feathers, so that they closely resemble females during the winter. Goldfinches start their partial molt in February, and in the next month or two, males will once again become bright yellow beacons. No-one can illustrate the subtle seasonal plumage changes of a male American goldfinch better than David Sibley: http://www.sibleyguides.com/2012/05/the-annual-plumage-cycle-of-a-male-american-goldfinch/ (Photo: male American goldfinch in March)

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