Egg and nestling mortality in red-winged blackbirds

Abstract

This study was undertaken to examine the mortality rates for the eggs and nestlings of small passerines. The Red-Winged Blackbird (Agelaius phoeniceus) was selected because of the availability of nests in the area. A marsh located on Goose Island about seven miles south of La Crosse, Wisconsin was used as the specific study site. The nesting period was examined from the first part of May until the middle of July. The results indicated an egg survival of 84%, a nestling survival of 60%, and an overall survival of 46%, with 35% of the active nests successfully fledging young. The egg and nestling survival produced a negatively skewed curve indicating a higher mortality for nestlings than for eggs, but when this data was added to adult survival it produced a positive skewed curve. A review of other studies showed wide variations in nesting success of Red-winged Blackbirds. Further studies should attempt a correlation of environmental data with nesting success.