Posts Tagged ‘foraging’

Tree sparrows, a goldfinch and a junco forage together.

Birds of a feather flock together…don’t they? The answer is “not always”. In winter, mixed flocks made up of several different species of birds are also common. If you watch a backyard feeder over an extended period of time, you might expect that, given a stable supply of food, there would be a steady stream of birds visiting. In fact, it is more usual for there to be an ebb and flow of groups of birds. Periods with many birds of a variety of species at the feeder are followed by lulls with few or no birds feeding. This probably represents the movement of mixed-species flocks through an area.

Junco (Junco hyemalis)

Dark-eyed Junco (Junco hyemalis)

Mixed-species flocks occur on every continent. Flocking seems to offer a number of potential benefits to members and there are a number of theories that seek to explain the purpose of mixed flocks. The convoy theory suggests flocks help to protect individuals because there are a large number of eyes and ears available to detect predators and perhaps confuse the predator when many individuals flee at once. The gang theory proposes that flocking may permit flock members access to resources within a territory whose owner would be able to expel individuals acting alone.

American Tree sparrows (Spizella arborea)

The beater theory notes that some flock members, in the course of their own foraging, flush prey that a different species can capture. However, the most compelling reason for mixed-flocking appears to be the opportunity it gives species to exploit available foraging resources in an efficient manner under difficult conditions. Temperate flocks average 10 to 15 birds of 6 or 7 species. This allows different species to take advantage of different foraging niches with limited competition.

Black-capped Chickadee (Poecile atricapilla)

Black-capped Chickadee (Poecile atricapilla)

Dominant individuals may benefit more because they can usurp the best sites, but foraging in flocks may help ensure that an individual finds at least some food before its energy reserves are exhausted. Thus, small birds with limited fasting abilities tend to flock more than large birds. Typically, a nuclear species provides the main element of a flock structure, with the flock composition changing as it moves along, a result of new individuals joining and others leaving. In the northern woodlands, chickadees are a common nuclear species. However, chickadees are difficult to observe as part of a flock at a feeder because their feeding behaviour involves individuals grabbing a seed and retreating.

White-breasted Nuthatch (Sitta carolinensis)

White-breasted Nuthatch (Sitta carolinensis)

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It’s not too unusual to see a flock of wild turkeys (Meleagris gallopavo) when you’re travelling local rural roads. This is especially so in winter, when the large birds show up starkly against snowy fields as they forage. It hasn’t always been that way though. I certainly never saw turkeys when I was growing up. Although wild turkeys are native to southern Ontario, its only Canadian locality, habitat loss and over-hunting decimated the turkey population during the 1800s. The species was extirpated from Ontario by 1909. The last confirmed sighting was in Aurora, north of Toronto.

A program to restore wild turkeys to Ontario was undertaken by the Ontario Ministry of Natural Resources (OMNR) and the first 74 wild turkeys, imported from Michigan and Missouri, were released in 1984. Since then, additional birds have been imported and released with considerable success, with large population increases over the last two decades. The OMNR ended its release program at the beginning of 2005. It still seems something of a novelty to see flocks strutting and gleaning seeds in fields.

Turkeys do well where there is adequate forest cover, a water source, and open fields, such as corn and soybean fields, for foraging. When spring days begin to warm up, the winter flocks break into smaller breeding groups, with dominant males preventing subordinate males from accessing females. The females construct nests by scratching a depression in the ground in an area where it will be well concealed by grass and vegetation.

When snow is very deep, it limits the availability of food, as the turkeys are unable to forage on the ground. If snow depth exceeds 25 centimetres for more than seven weeks, turkeys may begin to starve to death. Good luck, turkeys. Hope to see you in the spring!

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