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May 1999
At this spring season, everywhere in nature activity is aimed at the continuation of the species. Mammals, amphibians, reptiles, birds, insects, trees, plants - all living things - have unique adaptations for all aspects of life, including breeding, that help each species survive.
Birds' nesting habits illustrate the wealth of adaptations. There are differences in territory size, the area a breeding pair protects against other members of the same species. Height and placement of nests differ among species, and helps reduce competition for nest sites. There are different preferences for nesting materials. Examples of three bird species' nesting habits will demonstrate what I mean.
Tufted titmice are year-round residents in Maine and, although not brilliantly colourful, they have great charm. The four individual titmice frequenting our feeders until recently were likely a family group, the pair and two offspring from last summer. Late in the winter their territorial behavior began and last year's offspring dispersed to find mates and establish their own territories. The original pair is now in the process of nesting. The male sings from prominent perches to announce their territory of two to five acres.
It is a bit unusual, but titmice may form pairs any time in the year. Once paired they always stay together, communicating by calls. The pair selects a tree cavity or birdhouse where the entrance hole is at least one and a half inches in diameter. The site may be three to ninety feet above the ground. They explore all available cavities before choosing one, and then the female spends six to eleven days building the nest. The materials she uses are moss, bark strips, wool, cotton, leaves and hair. I put cat hair in the shrubs for their use.
Bobolinks winter in South America. When they return to Maine for the summer, two or three females pair with one male and nest in his territory of three to twelve acres which he barely defends. The female bobolink builds a nest of coarse grass, stems and rootlets, with a lining of finer grass. It is well concealed, in a slight hollow in the ground amid dense vegetation. Each female has one clutch of eggs in a season. Bobolinks' habitat is hayfields, meadows, marshes or fallow fields, and they sometimes prefer moist lowlands to upland habitats.
It is believed that bobolinks were native to the grasslands of the midwest. Their range expanded eastward as the forest was cleared for farming and meadows appeared in the landscape. Now, the populations of bobolinks and other grass-nesting birds are declining in their range in eastern and northeastern United States. This is due to changes in haying practices, where cutting takes place before nestlings have time to fledge, and because of the loss of agricultural land to development and reforestation.
Mourning doves are at the northern extreme of their range here in Maine. Like titmice, they have a lifelong monogamous pair bond. The male begins the selection of nest sites, leading the female about the area until she chooses one, which might take her several days. The male protects a territory two to fifty yards around the nest, although sometimes this species tends toward colonial habits when several pairs nest in the same tree. Nests are located on a horizontal limb, a vertical fork, or sometimes in tangles of shrubs or vines. Height from the ground ranges from three to thirty feet. Very often, the nest site is in a solitary coniferous tree. My neighbor's white pine that stands on the boundary between our yards is a favorite nesting location for several pairs of mourning doves.
The male and female mourning doves are involved in nest building. The male collects grass, weeds, twigs and pine needles and brings them to the female at the nest site. They may both arrange the materials, and the nest is completed in one to six days. The nest itself is a flat platform, loosely constructed, which does not fare well in storms. Mourning doves usually have two or more clutches of eggs each year.
Adaptations are a way that each species establishes a niche to survive in the world, where adequate food, water and cover are available in the habitat. It sounds so technical; the reality is magical.
By Nancy Coverstone (ncstone@umext.maine.edu), University of Maine Extension Educator in Androscoggin and Sagadahoc Counties
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