Return of the Juncos

When we think of bird migration, robins flying south and vees of Canada geese come to mind. However, there are many variations on the theme of migration. For example, American Goldfinches are short-distance migrants. Although we see goldfinches year-round here, the birds we see in summer aren’t the same individuals as the birds we see in winter. The summer breeders move a few hundred miles south. They are replaced by another flock of goldfinches that, to our undiscerning eyes look just the same, and arrive from a location farther north.

Dark-eyed Juncos (Junco hyemalis) are northern breeders, migrating to the Canadian Shield and Hudson Bay Lowlands for the nesting season. In winter, they migrate back to Southern Ontario and points south. I spotted my first junco of the winter on Monday, as it flew up from the lawn where it had been foraging and disappeared into a thicket. Juncos are easily identified in even a short glimpse by their distinctive tail feathers. The grey fan is flanked on each side by a stripe of white that leaves no doubt as to the identity of the fleeing bird.

These photos are a bit blurred because I just shot them through the porch screen, a record of the first winter foragers preparing for the long, cold season ahead.

Read Full Post »

Mixed Flocks

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.

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)

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)

Read Full Post »