This post was contributed by Alex Cook, co-author of a paper in a recent issue of the The Wilson Journal of Ornithology documenting the successful translocation of Saltmarsh Sparrow nestlings to a new nest after the loss of their parent to a predator.
In a dynamic ecosystem like the tidal salt marshes of the northeastern U.S., nests can be more likely to fail than to succeed even in the best of times. With daily influxes of saltwater and no cover from woody vegetation, it’s an ecosystem that few terrestrial vertebrates call home. The Saltmarsh Sparrow, however, is one of the few species to spend its entire life cycle in the salt marshes of the Atlantic coast, building a small cup nest close to the ground in the grasses in higher-elevation patches of the marsh.
This species has only a short time window between monthly lunar high tides to fledge their chicks before the marsh entirely floods and drowns any remaining nestlings. As sea levels rise, these delicate marshes are being squeezed between the rising seas and urban inland borders, leading to massive habitat loss and increasing the likelihood that nests will be flooded more often. Salt marsh-dependent species like the Saltmarsh Sparrow are already facing low breeding success and sharp declines in population size, and recent population models predict that the Saltmarsh Sparrow could reach functional extinction as soon as 2035 due to the effects of flooding on nest survival (Field et al. 2017). With such steep declines, Saltmarsh Sparrows are being studied throughout their range as conservationists desperately try to develop strategies to stave off extinction.
My research was conducted in the urban marshes of New York City and Long Island, where I studied the habitat selection and nest survival of these highly specialized species in a unique urban setting. My crew and I spent many hours in the field, systematically combing through the marsh grasses in search of the small, concealed nests of tidal marsh birds. Nothing gives you an innate understanding of habitat selection quite like having to locate dozens of nests that have been carefully hidden in tall grass! We would start each day by checking on all the active nests that we had already found. On days after extreme high tides, this can be a disheartening process, as many eggs and chicks get flooded out of nest bowls. Even on days without high tides, we still often found nests that had fallen victim to predators. In the urban marshes of New York, raccoons and feral cats are very active and prey upon both nests and adult tidal marsh birds.
At our suburban site on Long Island, we only had a small number of breeding Saltmarsh Sparrows and did our best to band and tag all of the adults, allowing us to associate individual females with their specific nests. Saltmarsh Sparrows are not a monogamous species, and males have no part in constructing nests, incubating eggs, or feeding chicks, leaving that solely to the females. Although you do your best to remain objective, if your study involves marking individual birds and then following the progress of their nests, it can be difficult to not become emotionally invested in their success. For my study species, this often lead to heartbreak.
One morning during nest checks, my heart sank when we saw fresh raccoon tracks in the mud around Nest 016. To my relief, there were still two living chicks, but they seemed unusually hungry, begging incessantly when we were checking them. Then, a few steps away, we found the mother dead in the marsh grasses, identifiable by her band number. Checking in on birds’ lives every few days and getting to observe their life cycle up close is what I love most about studying nesting birds, but I knew that without her, these chicks would surely not survive, as female saltmarsh sparrows are single mothers. Not wanting to leave the two chicks, I reached out to my advisors to discuss my options. I noted that another nest with four similar-aged chicks was nearby. A brood of six chicks is not unheard of for a Saltmarsh Sparrow, and the insects that sparrow mothers feed their chicks are highly abundant in the salt marsh, so we that felt adding two extra chicks to this nest would not place too much of an extra burden on the parent of this second brood. I also knew that Saltmarsh Sparrows are declining at rate a nine percent per year, with no good conservation strategy to halt their path to extinction (Correll et al. 2017), and that the fate of the species is so precarious that new approaches must be tried.
It was very exciting to pick up the chicks and carry them over to their new nest, hopefully giving them a chance to survive, but I was also nervous because I did not want to have a negative impact on the host nest. After a few more nest checks, I confirmed that the host chicks and the translocated chicks were all developing properly, and we were able to band them all before they fledged from the nest. I think Saltmarsh Sparrow females are some of the hardest-working bird moms out there. This female was able to successfully feed and raise six chicks all on her own, and she may have even re-nested again that season. It was very satisfying to know that we helped these chicks survive and that chick fostering potentially could become another tool in our conservation repertoire. However, knowing what we know about climate change and sea level rise, this unique species is going to need a lot more than a few chicks fostered here and there to persist. Still, I can only hope that those two chicks we helped will return to breed and contribute to the Saltmarsh Sparrow population.
Saltmarsh Sparrows are a priority species for many working groups and are being studied throughout their range. To learn more about Saltmarsh Sparrows and other tidal marsh bird species, check out the research and conservation of the Saltmarsh Habitat and Avian Research Program (SHARP) at tidalmarshbirds.org and the Atlantic Coast Joint Venture at acjv.org.