Archive for June 23rd, 2006
wild-bird-watching.com
The Tree Swallow leaves its wintering grounds along the seacoast from the Carolinas to California to begin its season of mating and nesting habits.
Description
Tree Swallows are 5 to 6 inches long. The Male has iridescent blue upperparts and bright white underparts. In fall, the upperparts may appear greenish. The female has duller, brownish upperparts and grayish underparts.
The female has an immature plumage in the 1st year (sometimes 2nd year). This allows her to approach breeding adult birds and their nest without being chased from the pairs nesting site.
If anything happens to the breeding female and she dies, the younger female bird can replace her.
This helps ensure a successful breeding season.
Mating Habits
Soon after arriving on their breeding grounds in mid March to mid April courtship begins. The birds perch near their nest holes or on top of nesting boxes. Flutter-flight and bowing displays from the male are done in front of the females.
Ocassionally one may see these birds billing. This is the pratice of a mating pair touching bills with one another. Actual mating occurs about a week before egg-laying begins.
Nesting Habits
Tree Swallows prefer open areas near water or in dead trees at the waters edge for nesting.
This bird is a cavity nester and is an ideal candidate for man-made bluebird bird houses. Competition from House Wrens and House Sparrows makes it even more important to place and monitor bird houses for these graceful flyers.
These birds defend only the nest itself. If predators or human visitors approach the nest while the birds are around, the birds may swoop down toward the intruder, turning at the last minute just narrowly missing the intruder. The nest is built primarily by the female, although the male does some gathering of materials. Cup shaped and made of grasses for a foundation and lined with feathers.
The nest building process can take as long as a month but generally completed in 2 to 3 weeks
The female lays 4 to 7 white eggs which are incubated for 13 to 16 days. Sometimes, during egg laying and even incubation time, the nest may be abandoned for a few days.
During this time you’ll see no activity around the nesting site. Within 3 - 4 days the birds return.
This leave-of-absence apparently has no effect on the success of the young birds hatching, only delaying the event.
The female performs the job of incubation and both parents feed the young. The young birds will leave the nest in 16 - 24 days after hatching.
1 - 2 broods each season.
Feeding Habits
The diet of the these birds consist mainly of insects caught on the wing. In winter bayberries are a favorite food. By late July or early August the Swallows leave their breeding grounds and form flocks around marshy areas where there are plenty of flying insects.
In early fall the Tree Swallows will begin migrating southward. In winter they feed in large flocks until early spring migrating back in much smaller flocks.
June 23rd, 2006
enature.nationalgeographic.com
Cliff Swallows are colonial — that is, they nest in colonies, sometimes numbering in the thousands of birds. In many ways the members of a colony appear to display remarkable social cohesiveness. They work together to mob predators and will even learn from each other where the good food sources are. But if you look closely at a Cliff Swallow colony, you’ll see that this seemingly cooperative community also harbors its share of dastardly misbehavior.
In every colony there are a few swallows (you might call them bad eggs) that parasitize their neighbors. They do this not by sucking other swallows’ blood or stealing food, but by putting their eggs in nests other than their own. Sometimes the sneaky swallow will even toss out one of the nest owner’s eggs before laying her egg in its place! This behavior is known as brood parasitism. The extra eggs go undetected, and the surrogate parents end up doing the work of raising the slacker’s young.
These parasitic egg-laying visits are clandestine and quick, but some Cliff Swallows have been spotted launching an even faster, more remarkable sneak attack: carrying eggs in their very small beaks (adapted for catching tiny insects on the wing) and quickly dropping them into a neighbor’s nest. Incoming!
Cliff Swallow Petrochelidon pyrrhonota (Hirundo pyrrhonota
Family: Hirundinidae, Swallows view all from this family
Description 5-6″ (13-15 cm). Sparrow-sized. A stocky, square-tailed swallow with pale buff rump. Upperparts dull steel-blue; underparts buff-white; throat dark chestnut; forehead white. Southwestern birds have chestnut foreheads. Cave Swallow of Texas and Southwest is similar but smaller, with darker rump and pale buff throat.
Habitat Open country near buildings or cliffs; lakeshores and marshes on migration.
Nesting 4-6 white eggs in a gourd-shaped structure of mud lined with feathers and placed on a sheltered cliff face or under eaves. Nests in colonies.
Range Breeds from Alaska, Ontario, and Nova Scotia southward through most of United States except Southeast. Winters in tropics.
Voice   Constant squeaky chattering and twittering.
Discussion As its name implies, this swallow originally nested on cliffs. The introduction of House Sparrows was a disaster for these birds, since the sparrows usurp their nests and often cause the swallows to abandon a colony. Long, cold, rainy spells while the young are in the nest also cause widespread mortality since the adults are unable to obtain enough insects. In California they often return in early spring to ancestral colonial breeding sites. If it turns chilly, however, they will abandon the area until weather and feeding patterns are more favorable, and return “on schedule” for their publicized arrival on March 19 at Mission San Juan Capistrano.
June 23rd, 2006
beheco.oxfordjournals.org
Anders Pape Møller
Laboratoire de Parasitologie Evolutive, CNRS UMR 7103, Université Pierre et Marie Curie, Bât. A, 7ème étage, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France
Address correspondence to A.P. Møller. E-mail: amoller@snv.jussieu.fr.
Among bird species in which males contribute to nest building, sexual selection has favored larger nests. I investigated determinants of nest size in the barn swallow Hirundo rustica and how nest size changed during the period 1977–2003, when tail length (a male secondary sexual character) increased by more than 1.2 standard deviations. Males with short tails contributed more to nest building than long-tailed males, signaling their future investment in food provisioning of offspring. Pairs of barn swallows were consistent in nest size when build ing new nests the same or different years, and level of phenotypic plasticity in nest size was small and could not account for temporal patterns in nest size. Offspring resembled their parents with respect to nest size, indicating a significant heritability of nest size, independent of whether offspring were reared by their parents or by foster parents, and there was a significant negative genetic correlation between male tail length and outer nest volume and amount of nest material. The temporal increase in male tail length was associated with a decrease in nest size, with the amount of nest material in 2003 on average being less than a third of the amount used in 1977. Temporal change in nest size could be accounted for by indirect selection on tail length causing change in nest size to match that predicted from change in tail length and the genetic correlation between male tail length and nest size.
Key words: barn swallow, heritability, Hirundo rustica, nest building, parental care.
June 23rd, 2006