Staying dry

Like Water off a Duck’s Back

text and photos by Dan Gleason © 2009

male Mallard

When it rains, we usually head indoors, but what do birds do in wet weather? Since birds have a high metabolic rate and need to seek plenty of food each day to fuel that metabolism, they can’t afford to wait for the rain to abate so that they can continue their normal daily activities.

Two different factors would seem to affect birds during wet weather: their food, especially insects, may be more difficult to find; and the birds themselves would get wet. Let’s look first at food availability.

During rain, especially heavy rain, many flying insects seek shelter and are more difficult for birds to find. The peak of our rainy season coincides with colder weather and during these months, many adult forms of flying insects are not present, but their eggs or larvae often over-winter. Flycatchers, many warblers, and other birds that depend on flying insects for food, have usually flown south to warmer environments where flying insects remain abundant. But even during cool, wet weather, there are many insects that do remain active on the surfaces of vegetation, on the ground, and among the detritus on the ground below trees and shrubbery. Bushtits flit from bush to bush seeking the insects that reside on the undersides of evergreen leaves or on the surface of winter twigs. Spotted Towhees and Fox Sparrows scratch at the ground, turning over decaying vegetation in search of insects and other invertebrates or seeds that may be present. Insect and spider eggs are also a common food for birds in the winter. Hedges and other dense shrubbery in your yard help provide a haven for insects, spiders or their eggs that are necessary for many of our winter-resident birds.

Many of the songbirds that do remain in our area throughout the winter (and there are many) seek seeds or over-wintering fruit to eat and thus do not depend on a steady source of insects. Chickadees, for example, change their diet, eating large numbers of insects during the summer and mostly seeds in the winter. House Finches and goldfinches do not switch diets seasonally, but continue to seek seeds throughout the year. The seeds at your feeders provide them with an easily accessible source, bringing these welcome visitors into our yards.

For large birds, such as raptors, many of their usual food resources still are active during the winter months. Many rodents remain active in winter so raptors that prey upon them have a steady supply of food. Some hawks, like Sharp-shinned Hawks and Cooper’s Hawks, feed on small birds, which are still plentiful in cool, wet weather. Sources of open water provide habitat for herons, ducks and other birds that seek fish or other aquatic food, including aquatic vegetation and the invertebrates that forage on such vegetation. Many shorebirds probe mudflats along the water’s edge in search of invertebrates to dine on.

So, finding food is usually not a problem for our winter birds even in the steady rain. But, do they get wet? As we stay out in the rain, our clothes become wet and we may begin to feel cool, wet, and somewhat miserable. Our skin may be waterproof but we still are uncomfortable. Of course, we know that ducks love water but how do non-water birds cope with being wet? In fact, under normal circumstances, birds seldom get “wet.” That is, their skin is not wetted, but is protected by a barrier of air, entrapped by their dense plumage of feathers. The fine structure of their feathers ensures that water does not penetrate to the skin.

You may have heard that waterfowl spread oil from an oil gland over their feathers to waterproof them. This may seem contradictory, especially when you consider that birds soaked in oil spills become wet and chilled. The truth is a bit more complex.

Mallard preening

At the base of the tail, on the upper portion of the rump, is the uropygial gland, also known as the preen gland or, sometimes, the oil gland. Secretions from this gland are not simply oils but are a mixture of waxes, fatty acids, lipids (fats) and water. As a bird preens, it rubs these glandular secretions throughout its plumage using the top of its head and its beak. This may provide some waterproofing, but the primary benefit of these “oils” is to keep the feathers supple and in good condition. The secretions may also provide some protection against bacteria, fungi, and lice or other feather parasites. Despite information in the popular press and even in many textbooks, there is little evidence that preen gland secretions provide much, if any, direct waterproofing of the bird’s feathers. The ability to repel water comes from the fine physical structure of the feather and only feathers in good condition can repel water. For this reason (and many others), preening is a very important activity for birds and one that consumes much of their time.

For some of you readers, a “backyard habitat” may include a portion of the coastline. For you, and for other coastal visitors, this discussion leads me to explain something about cormorants, as they are so often misunderstood. Perhaps you have seen cormorants with their wings out-stretched, drying their feathers in the sun. This observation has led some people to an erroneous conclusion, one often repeated in the popular press. It is often assumed that because the wings get wet, that cormorants do not have a preen gland. In fact, cormorants do have a preen gland, and although simple in structure, it functions quite well and serves the same purpose as it does in other birds. In fact, most of a cormorant’s feathers are waterproof. Without this protection for the body feathers, the bird would lose the insulation necessary to protect it from the cold temperatures of Oregon’s ocean waters. Only the cormorant’s wing feathers are “wettable”; the rest of the body remains dry. The air trapped beneath the feathers provides insulation and protection and it also provides buoyancy. This is a benefit that helps most water birds to stay afloat, but cormorants often dive deeply to feed and any added buoyancy can be a hindrance to diving deeply below the surface. The structure of the wing feathers is such that water can penetrate, wetting the wing and making it a bit easier to dive beneath the surface of the water. But only the wing is wetted and the body remains protected. Thus, cormorants can be seen standing on a rock or other perch with wings out-stretched in the sun to help them dry.

Brant’s, Pelagic and Double-crested Cormorants are the three species of cormorant found along the Oregon coast. Of these three, only the Double-crested routinely does this wing-spreading posture. This is also the only species of cormorant found inland, which means that you might very well see this display along our rivers, lakes or ponds, especially during the winter when these birds can be quite numerous inland. Look along the river and at Delta Ponds near Valley River Center where more than 100 of these birds can be seen early in the morning or again at dusk.

When you next find yourself out in the rain beneath your umbrella or bundled in your hi-tech raingear, look to the birds out in the same wet weather. It is then easy to admire how well the natural processes of nature have adapted them to survive our wet winter climate.

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