Monday, December 5, 2016

Invasive Species: House Sparrows in Winter

house sparrowHouse sparrows – those little brown and gray birds that flash mob the bird feeder – are common and easy to see. They’re quarrelsome, noisy, and when they’re on the ground, they move in vigorous hops that remind me of popcorn popping out of a pan.

They’re also an invasive species, scavengers that have hitched their wagons to humans, and at least on this continent, are having a very successful ride. Our farms, lawns, and grocery store parking lots provide all kinds of year-round foraging for these birds, and our structures provide them shelter. From gutter pipes to the bulb rims of traffic lights, house sparrows know how to make themselves at home in human-dominated settings, regardless of whether humans want them there.

Unfortunately, they are a real menace to bluebirds, purple martins, and many other native bird species. They’re extremely aggressive competitors for nesting sites. They destroy eggs, kill chicks, and will peck to death adult birds. Adding insult to death, they have even been known to build their own nests on top of their victims’ corpses.

This behavior isn’t pretty, but as the bird world goes, it’s hardly unique in its villainy. Cute little house wrens, for example, will sometimes destroy other birds’ eggs and young. House sparrows are reviled because there are just so many of them, and the frequency of their crimes is overwhelming. They’re prolific breeders, and this time of year they’re already preparing for next summer’s broods.

House sparrows are highly social birds that return repeatedly to the same hierarchically-organized flock in order to forage and roost. From August into September, you’re likely to see them massed together, looking especially scruffy as they go through their post-breeding molt.

By October, new feathers have formed, hormones are on the rise, and courting behaviors begin. The most obvious sign of this transition is the gradual darkening of the male bird’s beak color, which turns from yellow and gray to uniform black in winter. The male’s black chest badge may also serve as a courtship display, and studies suggest that its size roughly correlates to status in the flock. The bigger the badge, the more a male is likely to be a dominant bird with multiple mates. Male courting behaviors including intensive chirping at females, and rapid vibration of lowered wings.

By November, some house sparrows have established mate bonds. They may visit nesting sites from previous years, or stake out new sites. Courtship behaviors simmer down with the colder temperatures, but erupt in warm spells throughout the winter, and hormones continue to build. By the time favorable weather for nesting arrives, well before many of our migratory songbirds return, there will already be house sparrow couples committed to nesting sites, and primed to breed. Others will pair off during the spring breeding season.

Once house sparrows begin to raise young, they continue do so with gusto throughout the summer months. A sparrow pair can produce multiple broods in one year. The number of broods, and recovery intervals between them, is dependent in part on environmental factors. Ironically, nest boxes, which many of us put up to support the recovery of bluebird populations, are ideal sites for you-know- who.

If you’d prefer not to shelter these birds, understanding their winter courtship behavior is a good first step. If you see them around your home this winter, consider boarding up nest boxes until early spring, so they won’t develop an early attachment to these nesting sites (although this does mean less cold weather shelter for other wildlife). To be guaranteed sparrow-free, however, there’s no avoiding the hassle of monitoring boxes throughout the breeding season.

You can also take a philosophical view. While house sparrows are a hard bird to like, I’ve felt a (little) more friendly towards them since learning that they are in decline in much of their native range. In England, for example, the species has dropped an estimated 70 percent since 1977, according to the British Trust for Ornithology. The cause of this decline is poorly understood, but a loss of insects from pesticides and changes in agricultural practices are commonly cited factors. Hitching your wagon to humans is always a gamble.

Elise Tillinghast is executive director/publisher of Northern Woodlands magazine. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine, and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.

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5 Responses

  1. John Jongen says:

    Based on personal observation of bird species on our half-acre wildlife sanctuary adjacent to the Erie Canal for the past 35 years I have noted a marked decline in the numbers of several sparrow species visiting our gardens and feeders. At the same time there has been an increase in diversity and numbers of other species, except for the house finch that is also in decline. The few dozen remaining sparrows live and feed comfortably with the cardinal finch, the migrating gold finch, the junco, the Carolina wren, the blue jay, the blackbird, the migrating hummingbird, mourning dove, catbird, cowbird, woodpeckers, sapsucker, migrating oriole, blue bunting, crows, kingfisher, nuthatch, titmouse, chickadee, wood duck, mallard duck, red-tailed hawk, sparrow hawk, migrating robin, and greckel.

  2. Gerry Rising says:

    One thing about getting old, you recall some events about which others know little. A case in point is the longer-term history of the house sparrow in this country. When I was young and horse-drawn carts were still widely in evidence, the number of house sparrows was far greater than at any time since. The birds fed on the horse manure and their population declined sharply when those urban carts were replaced by motorized vehicles.
    Then when house finches first spread through the eastern states, their sheer numbers displaced house sparrows and house sparrows declined still further. But house finch numbers were devastated by conjunctivitis (what we used to call for humans, pink eye) and since then house sparrows have regained some of those losses. My personal estimate of their current population is about 20% of what it was in the 1930s.

  3. Charlie S says:

    “their current population is about 20% of what it was in the 1930s.”

    Have you read the latest reports on declining bird populations in this country? Very depressing…if you like birds that is.Habitat loss is a big factor but predation by cats is another. Cats should be kept indoors or if they’re allowed out of doors bells should be placed around their necks. Tell that to a simpleton! Many birds fly into windows or buildings and now we have this big push for windmills which is surely going to wipe out a great number of our beloved feathered friends.

    • Boreas says:

      Don’t leave out the broad commercial and individual use of insecticides and other poisons, as well as habitat changes, warming trends, and even noise and light pollution. Invasive species – both plant and animal – are yet another major factor. Birds are under a lot of stresses – some can cope, others can’t.

  4. Charlie S says:

    Yes Boreas and a very sad affair indeed.We’ll continue on our destructive path until there’s nothing left. It’s in our nature to be this way!