Floating into Fall – Habitat Islands for Sparrows

By: Bri Benvenuti @UNH

Floating islands in at the end of the field season in August. Photo: B. Benvenuti

Floating islands in at the end of the field season in August. Islands design courtsey Chris Steb and BioHabitats Inc.  Photo: B. Benvenuti

Over the past two summers, we’ve been experimenting with the use of floating habitat islands for increasing the nesting success of Saltmarsh Sparrows (i.e. via decreasing nest flooding). We view this as one of several possible short-term, targeted management efforts that may be needed in the near future to protect critical populations while habitat creation occurs in the longer term.  The need is imminent, given the documented increase in nest flooding rates, which will increase further as sea levels rise.

In late May of 2015, we placed four artificial, floating habitat islands vegetated with plugs of the high marsh vegetation Spartina alterniflora and Spartina patens in tidal marsh pools in Wells, Maine, after having a successful pilot season.  These new islands remained floating and free of tidal flooding throughout the season, demonstrating a highly successful structural design.  Initially, we encountered some challenges with maintaining healthy growing plants, due to a combination of factors, including an unexpected heat wave and drought in late spring immediately upon planting, small plugs with inadequate soil substrate and root development, and lack of acclimation to salt water by plants grown in a greenhouse with freshwater. We were able to overcome these challenges by subsequent plantings with healthier plugs, gradually acclimating plugs to salt water conditions prior to planting out on the island, and developing a watering regime for the islands post-planting. Through these modifications, we established four islands with healthy plants.

An example of Spartina patens sending new shoots up through the mat. Photo: B. Benvenuti

An example of Spartina alterniflora sending new shoots up through the mat. Photo: B. Benvenuti

At this time, the plants are robust and have exhibited extensive growth, both vertically and horizontally, including the sprouting of new shoots laterally through the substrate. Given these outcomes, we assessed the first phase of this project to be successful, i.e., we have demonstrated the establishment of healthy vegetation on floating islands, free of flooding, through four tidal cycles.  Our initial success holds great promise for the feasibility of floating habitat islands as a short-term management activity to increase successful reproduction of Saltmarsh and Nelson’s Sparrows. Now that we have evaluated and optimized the island construction methodology and implementation, the next step is to evaluate whether the island vegetation would provide a suitable nesting habitat for sparrows over 2016.

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