Effects of urban development on Mallard nesting ecology in the northeastern United States

The eastern Mallard (Anas platyrhynchos) population has declined since the mid-1990s, possibly because of increasing forest cover and urban development in the northeastern United States and Canada. Mallards are habitat generalists and nest throughout the Northeast, including in urbanized landscapes in southern New England. Although high Mallard nest survival has been documented at some developed sites, the effects of urbanization at a larger scale on nesting Mallards remain unknown. We assessed Mallard nest survival and nesting habitat in Connecticut in 2021–2023 to evaluate if anthropogenic development negatively affected Mallard nesting ecology. We located and monitored 74 Mallard nests without a marked female using field searching and public reports. We also captured and deployed GPS-GSM transmitters on 60 Mallard females captured when not nesting; we detected nests from 15 of 39 (38%) GPS-tagged resident females in 2022 and 15 of 33 (45%) resident females in 2023. Nest survival over a 37-day nesting period was 0.202 (0.126–0.291, n = 109 nests) during the three year study, which is within the range of estimates reported in the Northeast during the 1990s–2000s (0.13–0.51), suggesting that Mallard nest survival in urbanized landscapes is comparable to historical regional estimates, including those from non-urban landscapes. Survival was greater for nests on islands or hummocks but was not affected by anthropogenic development around the nest at multiple spatial scales. Nests located by using transmitters yielded survival estimates similar to nests without a marked female found by using field searching and public reports. Although transmitters can reduce bias in where nests are located and improve estimates of nest survival, researchers should consider effects of transmitters on female nesting behavior or biases of different search methods when interpreting results from transmitter-based studies. In urbanized landscapes, islands may provide valuable Mallard nesting habitat by offering separation from foraging mammalian predators. Management should prioritize creating or improving preferred nesting habitat on existing islands to encourage Mallards to nest where they have a greater probability of success.