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Bird Diets

American Goldfinches Dining On Thistle Seeds

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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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A Killdeer’s Diet

8-4-17 killdeer2 049A1132Ninety-eight percent of  a Killdeer’s diet  consists of animal matter.  Beetles, insect larvae, earthworms, grasshoppers and crayfish make up the majority of what a Killdeer eats. In the summer, adult beetles (see photo) and beetle larvae make up almost half of what they consume.

Much of the time we observe Killdeer they are running, stopping, waiting and then running again. This is typical feeding behavior. Another method of obtaining food consists of patting the ground or the bottom of a pond in shallow water with one quivering foot. Killdeer also engage in probing into mud and chasing prey, and they have been known to follow tractors in search of earthworms.

Food normally passes through a Killdeer’s digestive tract in about two hours, but the spore-bearing structures of some ferns that it eats take five to sixty hours. All birds have gizzards, where food is ground up. Some birds swallow grit to aid in the grinding process, and the Killdeer is one of them. It has been proposed that the sporocarps take longer to pass through a Killdeer because they are retained in the gizzard where they function as grit.

 

 


Cedar Waxwings Feasting on Fruit

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Cedar Waxwings are strictly fruit eaters in the winter, expanding their diet to include insects during the warmer parts of the year. As their name implies, one often finds these birds in areas where there are a lot of cedars, as they’ve historically fed on cedar berries in winter. However, they increasingly rely on the fruit of mountain ash as well as apple, crabapple and hawthorn in the Northeast. Waxwings run the risk of intoxication and even death after eating fermented fruit such as the apples pictured. In recent years Cedar Waxwings have started feeding on the fruits of invasive honeysuckles, a habit which ornithologists feel might be responsible for a shift in waxwing distribution as well as regional population increases.

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Small Birds Beware of Sharp-shinned Hawks

coopers-and-blue-jay-by-jeannieShort, powerful, rounded wings and a relatively long tail enable Sharp-shinned Hawks to maneuver in dense cover in pursuit of small birds, which compose 90% of their diet. Small mammals and insects are consumed, but not nearly as frequently as birds. The size of the birds eaten range from hummingbirds to Ruffed Grouse. Long legs and toes (especially middle toes) enable individuals to reach into vegetation and large eyes enhance its ability to catch fast-moving prey.

Sharp-shinned Hawks are familiar sights to those of us with bird feeders – this species is responsible for 35% of 1,138 predation incidents reported at feeders in continent-wide survey. In this photograph, a Blue Jay is successfully warding off an attack by a juvenile Sharp-shinned Hawk. (Photo by Jeannie Killam.)

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Attracting Fruit-eating Birds

7-11-16  birds and oranges 519.jpgThere are many birds, such as waxwings, that have a frugivorous (strictly fruit-eating) diet.  The only time they usually expand their diet to include insects is during the breeding season, when growing hatchlings require high amounts of protein for proper development.  Others, such as orioles, show a marked preference for fruit but also eat significant quantities of other foods.  All of these birds play an important role by spreading fruit seeds to distant areas either by caching food or distributing the seeds through their droppings.

Bird lovers often put out seed to lure birds in for a closer look (a practice discouraged during the summer in black bear country), but there is an equally effective magnet for some species, and that is fruit. (Due to the high sugar content, little nutrition and potential bacteria growth in jelly, it may be best to provide fruit over jelly.) Grapes often attract Northern Mockingbirds, Eastern Bluebirds, Cedar Waxwings, Gray Catbirds, Scarlet Tanagers, Rose-breasted Grosbeaks, House Finches and American Robins.  Raisins and currants (soaked in water overnight) appeal to Northern Mockingbirds, Gray Catbirds, Eastern Bluebirds, Cedar Waxwings and Eastern Towhees.  Species that find orange halves hard to resist include Red-bellied Woodpeckers, Northern Mockingbirds, Brown Thrashers, Baltimore Orioles, Scarlet Tanagers, Gray Catbirds and Rose-breasted Grosbeaks.  (Photo: Gray Catbird (left), female Red-bellied Woodpecker (middle) and female Baltimore Oriole (right) enjoying breakfast at The House On The Hill Bed & Breakfast, Greenfield, MA.)

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American Crow Bills Used As Tools

1-13-16  American crow tracks 147American crows obtain most of their food on the ground as they walk along in search of seeds, insects, frogs, snakes, bird nests and small mammals. Their hunting techniques are varied and most involve the use of their bill. In search of invertebrates, crows will probe the soil with their bill, flick aside leaves, dig in the soil and even lift cow paddies. They fish for tadpoles and dig nearly an inch deep with their bill for clams. In winter, their foraging continues and as these tracks indicate, when the snow is only a few inches deep they will walk around and around in a given area, probing tufts of grass for hibernating insects, mice, voles, or any other form of life these opportunists find.

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