Irruptions: evidence for breeding season habitat limitation in Piping Plover (Charadrius melodus)

Abstract

Effective management of wildlife populations requires identification of the factors limiting their growth. The Piping Plover (Charadrius melodus) is an imperiled, disturbance-dependent, shorebird species that nests on broad, sparsely vegetated beaches, sandbars, and lakeshores. In areas minimally affected by human use, plover habitat loss occurs through vegetation encroachment and erosion. Alternatively, habitat availability may be increased by sand deposition caused by storm-or flood-induced sediment transport or scouring that removes vegetation, or by receding lake levels. To test the hypothesis that plover populations are limited by available breeding habitat, we estimated the amount of habitat available before and after four significant storm and flooding events (i.e., disturbance) by classifying pre-and postdisturbance aerial imagery. We then evaluated the population changes that occurred after disturbance-related habitat alterations. Additionally, we report on population changes from four population increases that occurred after habitat creation events for which we did not have imagery suitable for classification. The storm and flood effects considered were those from hurricanes and nor'easters on barrier islands of Virginia, North Carolina, New York, and Maryland, USA, and those from floods and high water output from the Gavins Point Dam on the Missouri River between South Dakota and Nebraska, USA. The amount of nesting habitat increased 27-950% at these sites, and plover populations increased overall 72-622% after these events (increase of 8-217 pairs in 3 to 8 years after the disturbance, average 12-116% increase annually). The demographic changes were driven by productivity in some cases and probably by increases in immigration in others, and occurred simultaneously with regional increases. Our results support our hypothesis that the focal plover populations were at or near carrying capacity and are habitat limited. Currently, human interventions such as beach stabilization, the construction of artificial dunes, and dams reduce natural disturbance, and therefore, the carrying capacity, in many plover breeding areas. If these interventions were reduced or modified in such a way as to create and improve habitat, plover populations would likely reach higher average numbers and the potential for achieving recovery goals would be increased.

Habitat selection and potential fitness consequences of two early‐successional species with differing life‐history strategies

“…Both plovers and terns experienced exceptionally high nest and chick survival in the years following the floods (Hunt et al, ; Nefas et al, ), suggesting that predation and flooding were of little concern or that the densities were low enough that all birds were able to select relatively good habitat in this environment. It is unlikely that habitat was limiting the population immediately after the flooding (Robinson et al, ), and thus, it is possible that there were few if any birds that had to select marginal habitat. Similarly, cavity‐nesting species, which tend to have higher nesting success overall (Martin & Li, ), generally had the least congruence between selection and success among groups of birds, presumably because the pressure to select better habitat was less at such high success rates.…”

Piping plovers demonstrate regional differences in nesting habitat selection patterns along the U.S. Atlantic coast

“…Cohen et al (2009) found that peak density of Piping Plovers in the portion of their Long Island, New York study area where chicks had access to both ocean-and bay-side foraging habitat was more than double the density of Piping Plovers in adjacent habitat without accessible MOSH. All six Atlantic Coast examples of Piping Plover population irruptions following storm-induced habitat creation that are presented by Robinson et al (2019) occurred in New York-New Jersey and the Southern recovery units. Hence, carrying capacity and resulting population trends in more southerly latitudes-where plovers use more consistently available beach/backshore habitats less often-may be especially sensitive to natural processes that create washover habitat and to anthropogenic activities that accelerate its loss.…”

Contrasting long-term population trends of beach-nesting shorebirds under shared environmental pressures

“…Intrinsic factors provide dynamic feedback that affects population numbers, often with a time lag (e.g., density dependence: Turchin, 1999). Concerning breeding birds, studies report the effects of extrinsic factors (Plard et al, 2019) as well as intrinsic population dynamics, such as density-dependent recruitment, on population trends (Saether et al, 2002;Gunnarsson et al, 2005;Catlin et al, 2019;Robinson et al, 2019) or lack thereof (Wann et al, 2014).…”

“…Given the extent of human-wildlife conflict and enforced conservation actions at the seashores (Mansfield et al, 2011;Merritt and Shafer, 2012;Dundas et al, 2016), we also predicted that the annual number of park visitors and the presence of enhanced protection measures would affect population trajectory, especially at Cape Hatteras National Seashore, where there are 5 times more summer users than at Cape Lookout National Seashore (Table 1-(4 & 5)). Lastly, we included annual changes in habitat availability into our model as it is considered an important population driver for both species (Table 1-(6); Working Group et al, 2012;Robinson et al, 2019).…”