Survival of Mallard Broods on Benton Lake National Wildlife Refuge in Northcentral Montana

Abstract

BallDuckling survival was measured in broods of 31 radio-m arked hen mallards {Anas platyrhynchos) on Benton Lake National W ildlife Refuge in no rth-central M ontana during 1985 and 1986.Radio-m arked hens w ere located 1 to 7 tim es daily.Observations of marked and unmarked broods supplied data on duckling survival.Overall survival for the 60 day pre fledging period was 0.39, with 85% of the m ortalities occurring w ithin the first 18 days.Total brood loss occurred in 37% of all broods tracked, occurred within 24 days post-hatch, and accounted for 60% of all duckling losses.Broods th at survived to fledging averaged 5.0 ducklings.Ducklings in broods that hatched early (before 1 0 -June) had a 6 0 -d a y survival probability of 0.44, significantly higher than in late broods (0.33).A significant correlation existed (r = 0.46, P = 0.03) between condition index of hens fledging broods and the number of ducklings they fledged.Condition index of hens declined as the season progressed.Mean brood size did not differ significantly between broods of radio-m arked and unmarked hens.