Meeting Abstract

P1.31  Saturday, Jan. 4 15:30  Nest mortality in two species of passerines at high altitude MORTON, M. L.*; PEREYRA, M. E.; Univ. of Texas – Pan American; Univ. of Texas – Pan American pereyrame@utpa.edu

Major storms sometimes cause mortality in migratory birds in passage and also during their residency on breeding areas. This has been quantified to some extent, almost always in relation to the actions of a single storm, and usually on a single species. The frequency, type, and outcome of these storms is difficult to predict, challenges that are almost certain to grow with changes in climate. Herein we provide data on two species of summering birds, White-crowned Sparrows (Zonotrichia leucophrys)and Dusky Flycatchers (Empidonax oberholseri) breeding on the same subalpine meadows in the Sierra Nevada Mountains, and compare nest mortality caused by 16 storms during an 11-year period. Of the three types of storms involved, snow, hail, and rain, snow storms were most damaging to eggs, accounting for 90.3 % of 248 egg deaths in White-crowned Sparrows and 71.7 % of 121 in Dusky Flycatchers. Hail storms caused the majority of nestling deaths being 44.9 % of 138 in sparrows and 78.8 % of 113 in flycatchers. When mortality was calculated as a percentage of eggs killed during each type of storm, the species did not differ, indicating that females of both defended their nests equally well. The same was true of nestling deaths due to snow storms, but their mortality rate was greater from hail storms in flycatchers and much greater from rain storms in sparrows. Survival tended to be greater in nestlings of both species that were older and able to thermoregulate.