Comparable use of tidal living shorelines and natural‐fringe marshes by herons and shorebirds

Abstract

Living shorelines (LSs) increasingly are implemented as a defense against coastal erosion and rising seas; however, their ecological function for wading birds has not been evaluated. Here, we compared heron and shorebird use of LSs (created fringe salt marshes with a wave break fronting the planted marshes) to natural‐fringe marshes (NFMs) in the Chesapeake Bay. We assessed the use between May and August in 2018 and 2019 at 13 tidal marsh pairs, each consisting of one LS and NFM site, with sites within pairs having similar surrounding land use and wave exposure. In each year, we assessed diurnal use with video cameras recording at least four 30‐min segments/day for a total of 677 h of video, and nocturnal/diurnal use with acoustic recording equipment recording 10‐min sound files every 2 h/day for a total of 160 h of recording. We quantified diurnal use by measuring the total time a species spent at a site, and nocturnal/diurnal use by estimating the probability of detection (i.e., presence/absence). We detected four heron and five shorebird species when data were aggregated across pairs and sampling methods. Using Bayesian mixed models, time of use did not differ between LS and NFM sites for great blue herons (Ardea herodias) and yellow‐crowned night‐herons (Nyctanassa violacea). In contrast, time of use was higher for green herons (Butorides virescens) and spotted sandpipers (Actitis macularis) at LS sites but tended to be higher for great egrets (Ardea alba) at NFM sites. The probability of detection did not differ between LS and NFM sites for great blue herons and great egrets (combined as “Ardea spp.” due to difficulty in differentiating calls under noisy conditions), yellow‐crowned night‐herons, and spotted sandpipers. Green herons and killdeer (Charadrius vociferous), however, tended to be detected more frequently at LS sites. Collectively, our research indicates that LSs are functionally equivalent to NFMs for herons and shorebirds. We hypothesize that the low‐profile rock sills of LS provide platforms for resting and preening and offer prey even when vegetated marshes are unavailable to short‐legged species during flooding tides. In addition to their established reduction of coastal erosion, LSs provide habitat for herons and shorebird species.