Piping Plover population increase after Hurricane Sandy mediated by immigration and reproductive output

Evaluating population-level responses to conservation action following large-scale disturbance can improve the efficacy of future habitat conservation measures. In October 2012, Hurricane Sandy storm surges cleared vegetation and opened inlets through the barrier islands, Fire Island and Westhampton Island, New York, creating Piping Plover (Charadrius melodus) habitat. Storm effects prompted an island-wide stabilization project, which had the potential to negatively affect novel Piping Plover habitat. Certain sections of Fire Island were designed to create and/or improve habitat (hereafter, restoration areas) to mitigate possible habitat loss or degradation. Since Piping Plovers in New York appear to be habitat-limited, we anticipated positive population growth following habitat creation. From 2013–2018, we captured and banded 152 adults and 353 chicks, and monitored 279 nests and 160 broods. We developed an integrated population model to assess demographic processes in response to hurricane created-habitat (2013–2018) and the creation of restoration areas (2015–2018). We observed positive population growth in three of five years, and overall growth through the period (λ =1.13). Immigration and reproductive output were correlated with population growth (r = 0.92 [95% CI = 0.22–0.98], and 0.84 [95% CI = -0.47–0.95], respectively). Compared to the rest of the study area, restoration areas had higher chick survival, and lower nest survival and after second year site fidelity. The result was population growth in restoration areas (λ =1.14) similar to the whole study area. In the short term, restoration areas seemed to mimic natural Piping Plover habitat. Vegetation removal, an important process in renewing natural Piping Plover habitat, likely will be necessary to maintain habitat suitability. Efforts to increase immigration of new breeding adults into the system, and to improve reproductive output, primarily by habitat creation or maintenance, are likely to have the greatest local effect on population growth.

Methods
We studied Piping Plovers on a 27-km stretch of Fire Island and Westhampton Island, during April to August, 2013–2018. We searched for nests by surveying areas while closely watching the ground and by observing adult Piping Plover behavior. When a nest was found, we collected the location using a Garmin (Garmin International, Olathe, KS, USA) or Trimble GPS unit (Trimble Inc., Sunnyvale, CA, USA). If a nest was found with fewer than four eggs, we backdated to an estimated initiation date assuming 1.5 days to lay each egg (Wilcox 1959, Haig and Oring 1988b). If a nest was found with four eggs or it did not increase to four eggs after four days, we floated eggs to estimate the initiation date (Westerskov 1950). We monitored all nests every one to three days until they hatched or failed and classed nests that hatched ≥ one chick “successful.”

Prior to 2013, all individuals in the study were unmarked. During each year, we trapped unbanded adults on nests using walk-in drop traps (Wilcox 1959) and banded adults using either a uniquely coded, field-readable UV-stable Darvic flag (Roche et al. 2014) or a unique combination of four color bands on the tibiotarsus (2013 only). We surveyed for adult Piping Plovers beginning in the spring of 2013–2018 (range: April 1–May 14), concluding in the late summer of each year (range: August 23–September 26). We surveyed all of the study area, including the restoration areas, every two to three days using linear transects approximately 100–300 m apart. We resighted marked birds using 20–60x spotting scopes. We associated adult Piping Plovers with a nest either by confirming incubation of banded birds using a spotting scope or by catching the adult on the nest.

We banded all chicks as soon as possible after hatch (age range: 0–13 days), following the same banding scheme as adults. We conducted brood surveys for each brood every one to three days until chicks reached 30 days old. We considered a bird fledged at 25 days post-hatch for consistency with past Piping Plover studies (Hunt et al. 2013, Catlin et al. 2015). We also collected auxiliary resightings of banded Piping Plovers outside of our study area but within the Atlantic Coast breeding range (North Carolina to Atlantic Canada; Catlin et al. 2015).

The included datasets were all used in an integrated population model to assess demographic processes in response to hurricane created-habitat (2013–2018) and the creation of restoration areas (2015–2018).