Nest-Site Selection by Mallards and Blue-Winged Teal in Relation to Microclimate

It is unclear whether female ducks select nest sites on the basis of microclimatic features. Therefore, we tested the nest microclimate selection hypothesis by concurrently monitoring temperature (T), solar insolation, and relative humidity (RH) at Mallard (Anas platyrhynchos) and Blue-winged Teal (A discors) nest sites and nearby randomly selected "nonnest" sites (hereafter "adjacent" sites). Operative temperatures (Te) were calculated for nest sites and adjacent sites. Mallard and teal nest sites received consistently less insolation than adjacent sites, but did not differ in Tor RH. Teat Mallard nest sites was more moderate than at adjacent sites; nest sites were cooler between 0800 and 1730 CST. This pattern did not exist for teal nest sites, which had consistently lower Te throughout daylight hours. Coefficients of variation for all microclimatic variables did not differ between Mallard and teal nest sites and adjacent sites. We examined interspecific differences in nest-site microclimate by matching data by date and stage of incubation. Teal nest sites received more insolation and experienced greater Te than concurrently monitored Mallard nest sites, but there were no interspecific differences in Tor RH. Our results provide only limited support for the microclimatic selection hypothesis, suggesting that other factors are more important determinants of nest-site selection in ducks.