Migrations mean rapidly changing skies

Posted: Friday, August 04, 2000

Even though the Fourth of July usually ends up being the peak of summer for Juneau residents, some bird species which breed in Alaska are already well on the way to their wintering grounds in Central and South America by this date.

Shorebirds such as western and semipalmated sandpipers are already moving south shortly after the summer solstice, and often mixed species flocks of several hundred shorebirds can be found on the Mendenhall Wetlands in early July.

These early migrants are sometimes birds whose nests have failed, but parental care is very limited in some shorebird species. Nesting female semipalmated sandpipers leave within two to eight days after their young hatch, while male pectoral sandpipers don't even wait for the eggs to hatch before they head south.

One of the real treats for Juneau birders this July was a flock of up to 30 Hudsonian godwits, a large shorebird with a very long straight bill and rusty barred underparts. This species is rarely seen almost anywhere in migration as it often flies tremendous distances non-stop on its way as far south as Tierra del Fuego, the southern tip of South America.

Although July has seen many birds already pass through Juneau on the way south, August is a peak migration month for many bird species and an excellent time to look for migrant birds of the woods, marshes and fields.

In contrast with the spring migration period, the birds are often quiet and inconspicuous and hidden by the thick late-summer vegetation. Given that juvenile birds often have different plumages than adult birds and some adult birds molt into a different non-breeding plumage, it also can be a difficult time to identify birds.

Even though you may not be able to identify all the birds, however, August can bring some exciting migration scenes when birds gather. For example, large flocks of migrant swallows can sometimes be found hawking for insects low along the Mendenhall Wetlands, especially on foggy days when planes at the Juneau Airport are also grounded. Migrant gulls also flock up in huge numbers along the intertidal reaches of streams to feast on salmon eggs and carcasses.

On a good day, up to 15 species of shorebirds can be seen on the Mendenhall Wetlands in August. Loose flocks of yellowlegs picking at the surface and dense flocks of dowitchers probing the mud with their long bills are usually especially evident along the dike trail.

Although long stretches of forest trails will often seem almost devoid of birds in August, it is often because these birds are gathered together in ``mixed species'' flocks. Warblers, kinglets and chickadees often form such aggregations at favored feeding sites or along woodland edges. Last year, a budworm outbreak in an alder grove about one-quarter mile along the paved trail from the Brotherhood Bridge attracted flocks of several hundred warblers and kinglets, along with a few flycatchers and vireos.

If one of these mixed-species flocks can be found, then it will sometimes seem as if the woods are suddenly full of birds. Often a good strategy is to try to determine which way the flock is moving and then stand still in an area close by and let the flock move by you. This will often let you get good views of the birds at close range.

Often robins and other thrushes also gather around shrubs such as elderberry to eat the red berries. Beginning in late August and September, mountain ash trees also attract large numbers of birds to feed on the ripening berries. Good areas to look for migrant flocks include trails at Sandy Beach in Douglas, the Dredge Lakes area, the Eagle River area and the mouth of Fish Creek. As in most birding situations, a pair of binoculars is essential to get a better look at the birds and a field guide will help you identify what you have seen.

As a final note, it should be mentioned that migrant numbers often vary tremendously from day to day, or sometimes even within a day. A woodland or marsh teeming with birds one day may be almost devoid of birds the next, especially if the skies clear overnight, because the birds often migrate when north winds are coupled with fair skies.

Often the best times to find August migrants are in short breaks between rain showers because low clouds and foggy weather ground both avian and human travelers.

Paul Suchanek is a fishery biologist for the Alaska Department of Fish and Game. The Juneau Audubon Society will resume monthly meetings in September. To make suggestions for future columns, or to share sightings and observations, e-mail Juneau Audubon Society members at ckent@alaska.net.



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