Breeding Ammospiza nelsoni (Nelson’s Sparrow) exploits both saltmarsh and hayfields in northern habitats

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Abstract Ammospiza nelsoni subvirgata (Acadian subspecies of Nelson’s Sparrow) breeds in saltmarshes from northern Massachusetts to New Brunswick and eastern Quebec. In the Canadian Maritimes, this subspecies also successfully breeds in diked agricultural lands (i.e., “dikeland”) that were originally created by Acadian settlers in the 1600s. Little is known about the reasons for or consequences of using dikeland for breeding. To fill this knowledge gap, we tracked male and female sparrows, and monitored nest fates in natural saltmarsh and human-made dikeland habitats. We collected fecal samples from adults and nestlings to examine which habitat type they were foraging in, and we also quantified vegetative cover. We hypothesized that flood risk in saltmarshes played an important role in the decision of A. n. subvirgata to nest in dikeland given that the saltmarsh is regularly inundated with tidal water. Based on nest monitoring, we estimated higher overall nest success in dikeland than saltmarshes. Fecal sample analysis showed distinct differences in diet between individuals using dikeland compared to saltmarshes. We also observed differences in vegetation. These results suggest that A. n. subvirgata are able to take advantage of a readily available human-made habitat for breeding. With rising sea levels and increased storm events threatening coastal habitats, it is important to understand if coastal-breeding birds can adapt to changes and what trade-offs exist for individuals who shift to alternative habitats.