Nesting Biology of Mallards in California

Abstract

We investigated mallard nesting biology in major wetland complexes in California from 1985 to 1989 to assess current productivity. Study sites were located in the Suisun Marsh, the Central Valley, and the intermountain region of Northeastern California. We located more than 5,500 nests of which 3,903 (70%) were mallard nests. Mallards began laying eggs in late February, and peak nest initiation occurred in early April at all areas except Northeastern California. Few nests were initiated after early June. The density of indicated breeding pairs was 20.8 ± 1.5 (x ± SE) per km 2 , and nest densities on study areas averaged 111 ± 17.9 per km 2 . Overall nest success (Mayfield method) was 32.3% (95% CL = 30.4-34.2). Clutch size declined from 10.3 eggs on 1 March to 6.9 eggs on 1 June. Brood size averaged 5.8 ± 0.15 ducklings per Class Ia-b brood (cf. Gollop and Marshall 1954) and declined to 5.2 ± 0.23 ducklings per Class IIc-III brood. We captured 1,014 nesting mallard hens; 37.6% were 1 year olds. In Suisun Marsh, where nesting densities were highest, 1-year-old hens were less frequently captured on nests during dry years. These findings indicate that mallard production in California is greater than previously recognized, and reproductive characteristics differ from those observed at northern breeding grounds.