Thursday, October 9, 2014

White-Throated Sparrow Migration

white-throated sparrowNumerous amphibians and avian calls are enjoyed by Adirondack residents and visitors alike throughout spring and early summer, yet as the seasons progress, this music gradually subsides until by early autumn only a few bird voices can be heard amongst the fading background chorus of crickets.

Since singing requires an expenditure of energy, and advertising one’s presence increases the chance of attack by a nearby natural enemy, birds refrain from much vocalization after the breeding season ends. However, it is possible to hear the soulful call of the white-throated sparrow during the autumn, as there always seems to be an individual or two in one of the transient flocks spending time in the area that bellows out its characteristic “Old-Sam-Peabody-Peabody-Peabody” song.

The white-throated sparrow is a ground feeder that prefers to forage for its seeds in the brush along the edge of forests, among the low shrubs of bogs, abandoned fields, and lake shores, and in the grasses and weeds of lawns that have not been mowed for several weeks. Often a flock of white-throated sparrows joins a flock of juncos during the day, as both species have similar habitat and food preferences.

Despite its cold hardy nature, the white-throated sparrow is forced to abandon its northern breeding grounds in autumn as frequent periods of freezing weather increase their demand for food and the threat of a heavy, wet blanket of snow that would severely impact its ability to find seeds, reduces chances for survival. The white-throated sparrow repeatedly scratches at the layer of dead matter on the ground in an effort to uncover seeds that have recently fallen. Any covering of snow or freezing rain would limit this delicate creature from accessing food and jeopardize its existence.

As a general rule, older birds are the first to advance south because these individuals skilled at foraging can successfully develop the fat reserves required for a long distance journey weeks before the juveniles. In the Adirondacks, it is typically during September when the older birds begin their journey, and early to mid Oct. before the immature birds have acquired enough nutrients necessary to fuel a period of long distance flight. By the time the younger members of this species are ready to leave, they are often joined by older sparrows that have recently arrived in our region from much further north, thereby creating flocks of mixed aged individuals.

As is the case with many other migratory birds, the white-throated sparrow travels at night. This allows the bird the opportunity to feed throughout the day in order to place as many nutrients into its digestive system as possible to help fuel a prolonged period of flight. Once the flock lands, the birds typically meander throughout the general region for several weeks in their attempt to find plentiful sources of food. After the individuals have regained the fat depleted during the previous migratory session, the birds eat all day long before taking off for another 300 to 400 mile flight south.

It is believed by researchers that the white-throated sparrow’s brain has an internal magnetic compass that aids in navigation during migration. There is also evidence that prior to departing, this sparrow aligns this directional system using light from the sun. (Because the direction of the Earth’s magnetic fields depends upon location, a true south heading is different from locations in Canada compared to places in Central New York. The high concentration of iron ore in several places in the Adirondacks produces compass readings that are different from regions lacking in such mineral deposits. Additionally, our magnetic north pole is currently drifting to the west, which could influence the accuracy of a reading in far northern latitudes.) For these reasons, it is important for the birds to calibrate their navigational sensors before undertaking a flight south. It is also believed by some researchers that the position of certain stars are used to help keep the birds on course when flying long distances. However, cloudy skies could always interfere with this process, which is why magnetic orientation is believed to be their primary method of navigation.

It is not known why a few individuals spontaneously burst into song at this time of year. It is possible that their call is used to reaffirm a dominant position in the flock, or it may be that an individual may wish to impress a future breeding partner that has recently joined the flock. In any event, such a seldom performed act at this time of year is always a welcome treat to people that are outdoors, as this melody seem to be as much a part of the Adirondacks as the call of a loon. Some people always note the first time that they hear a white-throated sparrow in spring, yet not many ever note the occasion when they hear this mellow song for the last time in autumn.

Photo courtesy Wikimedia user Cephas.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

3 Responses

  1. Sally James says:

    A sweet article about my favorite bird. We are blessed to hear its call where we live in Virginia, and its song always takes me home to the Adirondacks. Thanks!

  2. Bill Ott says:

    Not only a great article, but a beautiful photo. Make sure to click on it to see all the detail.

  3. Wally Elton says:

    Found 14 of them (at least) in Saratoga Springs this morning. On two occasions, one started the song but cut it short.

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