COMPARATIVE REPRODUCTIVE-BIOLOGY OF 3 SPECIES OF SWALLOWS IN A COMMONENVIRONMENT

We compared the breeding biology of sympatric and contemporaneously br eeding populations of Tree (Tachycineta bicolor), Barn (Hirundo rustic a) and Cliff swallows (Petrochelidon pyrrhonota) in 1994 and 1995 in c entral New York to characterize their life histories under common envi ronmental conditions. Laying dates did not vary among species, but ave rage clutch sizes were largest in Tree Swallows (5.7 eggs), intermedia te in Barn Swallows (4.7 eggs) and smallest in Cliff Swallows (3.5 egg s). Two broods were common in Barn Swallows, but Tree Swallows raised only one, and we suspect that Cliff Swallows raised only a single broo d. Relative egg mass (egg mass/female mass) was higher in Barn than in Tree swallows. Most nests fledged young, and hedging success did not vary among species. Growth rates of four nestling traits were measured (mass, wing chord, tarsus and bill), and overall, Tree Swallows grew the fastest. Peak nestling mass was substantially higher in Cliff Swal lows than the other species, probably because they gained the most fat . A Literature survey of hirundinid growth rates also suggested that T ree Swallows grew faster than the other species. Per capita provisioni ng rates of parents (trips/nestling/h) increased seasonally and were h ighest in Barn Swallows. Slower growth despite high feeding rates sugg ests either lower feeding efficiency or more severe effects of ectopar asitism in Barn Swallows compared to the other species. Our results sh ow that clutch size, number of broods/season and the pattern of nestli ng growth vary among species and probably represent differences that h ave evolved because of differences in (1) the availability of suitable nest sites (i.e., the limited breeding opportunities hypothesis), (2) food supply, or (3) demographic trade-offs.