Great Basin Naturalist


Timing of reproduction was assessed for wild onions and White-crowned Sparrows in relation to snow conditions on the same subalpine meadow in the Sierra Nevada for 21 years. Flowering date and clutch initiation date were both highly correlated with snow conditions, being later as snowpack was deeper. Interannual variation in schedule was 46 days for onions and 33 days for sparrows. There was nearly a fivefold difference in snowpack depth, and date of snow disappearance varied interannually by 72 days. Compensation for late-lying snows occurred in both species but was greater in sparrows than in onions because the nest-building behavior of sparrows was flexible. In years of deeper snow, sparrows were able to lay eggs earlier because they built more nests than usual in trees and shrubs rather than waiting for groundcover to develop.