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Bird Diets

Spruce Grouse Foraging

While Ruffed Grouse are plentiful throughout most of New England, one has to go to northern Vermont, New Hampshire or Maine to see its cousin, the Spruce Grouse.  Associated with boreal forests, this largely herbivorous bird feeds primarily on the needles of pine, spruce and fir (a small amount of animal matter is consumed in the summer as well as ground vegetation). Especially in the winter, a large volume of conifer browse is consumed in order to meet energy demands.

The grouse holds the needle between the tips of its mandibles and breaks it off by flicking its head.  This action, and the fact that Spruce Grouse feed exclusively on needles in the winter, leads to the wearing off of the tip of the bird’s upper mandible by spring.

If you are searching for a Spruce Grouse, you might want to concentrate in the middle of the crowns of trees, as this is where the birds tend to forage. Theories for this preference include the fact that needles in this location have higher nutritive value, branches provide sturdy support, and grouse can see approaching avian predators while remaining partially concealed. (Birds of North America, Cornell Lab of Ornithology). (Photo: male Spruce Grouse browsing on Tamarack needles and (inset) looking for grit on the ground.)

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Hungry Barred Owls Near Feeders

3-4-19 barred owl _U1A2992Over the past few weeks many people in northern New England have discovered Barred Owls perching near their bird feeders during the day. At this time of year, with snow on the ground, food is harder to find and owls are forced to hunt during the day as well as at night. Bird feeders are a sure source of food, as mice and voles are coming out to feed on spilled seed (most often at night).

The owls we see are relying primarily on their sense of hearing to locate small rodents. Their ear openings are asymmetrically placed, which means that sounds reach the owl’s ears at different times. This helps them zero in on the exact location where the sound is coming from, both when they are perched as well as in flight.

Although Barred Owls can detect the sound of a mouse scurrying through tunnels two feet beneath the snow, this winter has been more challenging for them than many. Almost every snow storm has been followed by rain, which has created multiple layers of icy crust. Although sound may be heard through solid, liquid, or gaseous matter, one wonders if these multiple layers of crust compromise an owl’s ability to hear. In addition, these conditions can’t help but impede an owl’s ability to reach its target as quickly as it normally does.

A dear friend whose compassion for creatures big and small is unmatched was going to great lengths (coating balls of hamburger with hair cut from her dog’s coat so they would bear some resemblance to small rodents) to help a resident owl in a time of need. Some would argue that nature shouldn’t be interfered with, but those readers with a desire to come to the aid of a hungry owl could let a little seed fall on the snow that’s packed down around the feeder in hopes that a large supply of accessible food might attract more rodents which might fill more owl stomachs.

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Pileated Woodpeckers Foraging For Last of Wild Grapes

12-17-18 pileated woodpecker and grapes IMG_7731

Carpenter Ants and wood-boring beetle larvae are the mainstay of the Pileated Woodpecker’s diet.  Long slivers of wood in trees and logs are removed in order to expose ant galleries, creating large rectangular excavations.  The woodpecker’s long, pointed, barbed tongue and its sticky saliva enable it to catch and extract ants from the ants’ tunnels.

While ants and beetle larvae are consumed year-round, fruits and nuts are eaten when available. A study that took place in the Northeast found seasonal shifts in primary food items: fruit in fall, Carpenter Ants in winter, wood-boring beetle larvae in early spring, and a variety of insects in summer.

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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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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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