What do birds eat?
Back in 2012, I wrote a Dawn Chorus diary on birds' beaks and bills (http://www.dailykos.com/...) and how they evolved to help birds pursue their food sources.
Today, I thought I'd flip that around a bit and look at the food that birds eat with that variety of beaks and bills.
Let's take a look at a nice photo of a bird with a bit of food and then join me below the tangled orange spider nest bird feeder to consider this topic some more.
A Cedar Waxwing with a tasty berry
As we consider the topic of what birds eat, allow me to acknowledge that I have borrowed information from the following publication: Breeding Season; Hummingbirds, Nectar, and Water; Hoarding Food; Drinking. Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye. My humble thanks to these authors. (The photos are all mine, though.)
The authors tell us that birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds. Because birds have no teeth, their digestive system has adapted to process food items that are swallowed whole.
Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists. (And that previous Dawn Chorus I linked to talks about how bill shapes figure into all this.)
Time to intersperse a photo or two. Here's a Black Phoebe that has just captured a dandy dragonfly for lunch, followed by a Great Egret with perhaps the World's Tiniest Fish (a guppy maybe?).
Birds' feeding strategies vary by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Nectar feeders such as hummingbirds have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers.
Shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches.
Loons, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion, while aerial predators such as and terns plunge dive after their prey. Flamingos, and some ducks are filter feeders. Geese and dabbling ducks are primarily grazers.
Dabbling ducks that graze include Northern Pintails . . .
and Northern Shovelers . . .
and Cinnamon Teal
Some species, including frigatebirds, gulls, and skuas, engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet.
Whose fish is it? Gull tug-o-war!
Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.
Crows like peanuts, too
Birds eat many things that seem none-too-appealing to us: beetles, flies, spiders, earthworms, rotting fish, offal, poison oak berries, weed seeds, and so on. Not only that, most birds have diets that are quite monotonous -- some passerines may go for weeks on a diet composed largely of grasshoppers, Brants dine almost exclusively on eelgrass, and Snail Kites rarely if ever taste anything but snails. In spite of this, the nutritional requirements of birds are not very different from ours; they need proteins, fats, carbohydrates, vitamins, and minerals.
Western Bluebird snatches a berry
And a Willet finds something soft and crunchy
Birds use carbohydrates and fats primarily as energy sources, but proteins are needed for construction of tissues, enzymes, and so on. Reproduction, growth, and molting all require more nitrogen than simple maintenance of the body, and proteins are the source of that nitrogen. Birds, such as Red-winged Blackbirds, that are omnivorous (eating both plant and animal food) increase the proportion of protein-rich animal food they eat in the breeding season. Many that are herbivorous (primarily eating plant foods), such as sparrows, may subsist for much of the year on a relatively low-protein vegetable diet, but in the breeding season they take as many insects as possible, and often provide their young with a diet comprised entirely of insects.
Speaking of insects, this Northern Mockingbird has a catch
Here's an American Robin grabbing a berry
And with all this talk about food, here's a last photo to remind us that birds need water no matter what type of food they eat. Here's an enterprising Yellow-billed Magpie that has learned where he can count on finding it.
Please use this as an open thread to share your bird thoughts and photos. Have a great Sunday, happy birding to all, and Go Niners!