In April two male cardinals were singing on opposite sides of Cassey Brook and when a female ventured over the brook, one of the males flew down and seemed quite agitated about her incursion. At the time I thought I was witnessing the establishment of a territorial boundary, but I haven’t heard or seen those cardinals since. So perhaps I was witnessing courtship.
When we moved here in December, there was an old phoebe nest on a rafter inside the door-less garage. The phoebes returned in April and hovered around the garage, making a few trips inside, but apparently they felt we used the garage a little too often. They decided to nest in the barn across the driveway.
For most songbirds, territory is a physical space that they establish around their nest. It is primarily a place where a pair of birds has dibs on the resources. In colonial birds, such as some swallows or red-winged blackbirds, the definition of territorial space is more complex. Among red-wings, several females—5 to 15—will build nests in one male’s territory, which he will defend by singing almost constantly, taking no part in nest building or feeding of the nestlings.
Barn swallows, on the other hand, defend a small territory immediately around the nest and have shared foraging grounds. Male barn swallows will physically attack an interloper near its nest, but hunt insects alongside the same bird over a nearby pond.
But the commonly observed model of a bird territory is an acre or so of landscape inhabited by two birds with one nest. Among common and aggressive birds like robins, these territories can be co-extensive and require frequent physical altercations to defend. Some birds, again like robins, have habitat requirements that are both generalized and widespread. Robins avoid extensive woodland and large open spaces; everywhere else is fair game. This habitat preference corresponds to their catholic diet, which includes all manner of invertebrates and even the occasional vertebrate plus seeds and berries.
In contrast, the red-eyed vireo, although common, is confined to mature, deciduous woodlands with shrubby understories. They shy away from even the edges of forests or ones that are too heavily coniferous. During the nesting season, half of their diet consists of caterpillars, which they pick from leaves at the ends of branches near the top of the canopy. The rest of their diet consists of beetles and flying insects.
The shrubby understory is necessary because, although the male forages in the canopy, the female builds the nest in an understory tree or shrub, 10 or 15 feet from the ground. Theirs is an equable relationship; the female builds the nest, but the male contributes materials. The male feeds the female while she is incubating, and both of them feed nestlings.
Furthermore, the female does her share of territorial defense, guarding the area immediately around the nest, while the male defends a larger territory, both with his truly incessant singing and with occasional physical altercations. In addition to intrusion by other vireos, this species must drive off brown-headed cowbirds, which frequently lay their eggs in vireo nests.
Ironically, the cowbirds do establish a breeding territory. But their criteria focus on what other bird species are nesting near good foraging grounds. Cowbirds forage primarily on the ground in open grasslands, but they parasitize many woodland birds like vireos. So, their breeding territory can include multiple habitats.
We think of songbirds as establishing territories in April and May, and nesting in May and June, with most rearing one or two broods. There are, in fact, all kinds of variations from this supposed norm. American goldfinches, for example, eat seeds almost exclusively and therefore must wait until flowers go to seed before they begin breeding. They need to have enough available to feed their nestlings.
Goldfinches favor the seeds of the aster family. Consequently, although they pair up in the spring they don’t begin laying eggs until July. Their breeding season may extend into September, when the warblers and other migrating birds have already gathered into flocks and have started to head for South America.
Goldfinches will defend their territories against other goldfinches before the female begins to incubate eggs. But once she is confined to the nest by her duties, the male goldfinches leaves off defending his territory and spends all his time feeding his mate and subsequently also the nestlings. This corresponds with the generally unaggressive behavior of this species, which holds the lowest position in the pecking order at every bird feeder and never joins other birds to mob predators.
Several bird species do not have fixed nesting periods and have either no territories or somewhat abstract ones. The red crossbill is a social bird throughout the year, wandering through coniferous forests in flocks, looking for an abundant cone crop. When one is found, the females may build their nests in a group very close together. The males establish singing perches and drive other males away from preferred cones. This is a very democratic species; both males and females incubate the eggs and feed the young.
The cedar waxwing is the most erratic departure from the norm. Because they eat mostly berries, like the goldfinches and the crossbills, they must wait until later in the year to breed, usually between July and September. However, they are not migratory, but nomadic. Consequently, you never know when they are going to show up. And when they do, there is no fixed period between their arrival and when they might breed.
When waxwings do build nests, the females often cluster together in loose colonies. This is primarily the work of the females, but the males occasionally pitch in. If there are nests of other birds nearby, the waxwings will occasionally filch materials from them to build their own nests.
Instead of defending territory, you almost expect the males to sit around playing the bongos and spouting poetry.
Bill Chaisson has been a birdwatcher since age 10. He is a former managing editor of the Eagle Times. He now lives and works in Wilmot. Contact him at firstname.lastname@example.org