A land manager's guide to conserving habitat for forest birds in ...

Male Chestnut-sided Warbler — Photo: Brandon Holden
FOREST BIRDS IN
ONTARIO
Well-concealed Chestnut-sided
Warbler nest in shrub — Photo: OMNR
In order to develop an understanding of the factors that affect songbirds on their
breeding grounds we must first gain some appreciation of their life cycle and basic
habitat needs.
Migration
Southern Ontario forests are home to nearly 100 species of breeding birds. One-third
(33 percent) of these are resident birds like the Black-capped Chickadee and Downy
Woodpecker, seen year round. The rest are migrants that breed and raise their young in
Ontario during the summer, and spend the winter in more southern locations. Some
migrants travel short distances (southern United States) to their wintering grounds,
while others travel up to 10,000 km to the Neotropics (Mexico, Central and South
America, and the Caribbean).
Migrant songbirds typically start arriving on the breeding grounds in southern
Ontario in early May, though the timing varies by species. Generally, older males will
arrive first, then younger males, followed by older females, and finally the young
females. These birds will have a few short months to nest—the success of their
populations hinging on how many young they will be able to successfully fledge from
their nests each year. Depending on the species, each pair will attempt to raise one or
two families (broods), usually of two to five young. This is no small task for most
songbirds breeding in forest fragments of southern Ontario, as they face a myriad of
challenges, including nest predation, nest parasitism by Brown-headed Cowbirds (see
below), and food limitations, all of which can have a strong impact on their ability to
successfully raise their young.
Despite this long list of challenges, by migrating from one place to another, birds
have evolved a way to take advantage of food and shelter that is scarce in certain
geographic areas at particular times. Habitats on the wintering grounds (like the
Caribbean) offer feeding opportunities that are not available during the winter on the
breeding grounds (like southern Ontario) when freezing temperatures eliminate insects
and other food resources. Habitats on the breeding grounds provide high insect
populations, long days, and breeding opportunities with less competition, compared
with the wintering grounds where migrants have to compete with residents and their
preferred food sources become scarce. In the end, it pays for migrants to make the
effort to relocate north to woodlots in southern Ontario each spring to breed, where
they can raise more offspring than if they had remained on their wintering grounds to
compete with resident birds breeding there.
Breeding Biology
Each species has a unique nesting strategy. Some, called cup nesters, build nests like
those of the American Robin, with sticks, leaves, plant fibres, strips of bark, mud,
spider webs, or animal hair. These cup nesters will place well concealed nests on the
ground, in shrubs or small saplings, or high in the canopy, depending on the species
and habitat. Others, called cavity nesters, build nests in tree holes. Cavity nesters are
divided into two groups: primary cavity nesters, like the Pileated Woodpecker, which
dig out their own hole; and secondary cavity nesters, like the Great Crested Flycatcher,
which use existing cavities (often made by primary cavity nesters, but include natural
tree holes) for their nest. Once a nest is constructed, birds will lay one egg a day until
Pileated Woodpecker cavity —
Photo: OMNR
Forest Birds in Ontario 15