Factors that affect renesting in Mallards (Anas platyrhynchos)

Renesting is an important strategy for coping with nest loss in many species of birds. We investigated renesting behavior of radiomarked Mallards (Anas platyrhynchos) breeding in the Canadian Prairie Parklands and found that females were persistent renesters, replacing >57% of 4,112 destroyed nests. Renesting propensity was most affected by nest initiation date, with ∼90% of unsuccessful females renesting if destroyed clutches had been initiated in April but <10% renesting for clutches initiated after 20 June. Probability of renesting declined with successive number of nesting attempts, but this was primarily an effect of initiation date. Renesting propensity increased with female age and body condition and declined for birds that had invested more time tending their previous clutch, but the latter effect was pronounced only among late-nesting females. The amount of time required to produce a replacement clutch was primarily a function of whether females were engaged in rapid follicle growth when nest failure occurred: 44% of females (383 of 870) that lost nests during early laying renested within 4 days, whereas only 2% (12 of 639) that lost nests after clutch completion renested within 4 days. Although clutch size was smaller in renests, this was entirely an artifact of later laying dates. Our results suggest that seasonal timing had the most influence on renesting behavior. Female age, body condition, and prior nesting effort had smaller, but demonstrable, influence.