Asymmetric benefits of a heterospecific breeding association vary with habitat, conspecific abundance and breeding stage

Abstract

Heterospecific breeding associations may benefit individuals by mitigating predation risk but may also create costs if they increase competition for resources or are more easily detectable by predators. Our understanding of the interactions among hetero-and conspecifics is often lacking in mixed species colonies. Here, we test how the presence of hetero-and conspecifics influence nest and chick survival for two listed (under the U.S. Endangered Species Act) migratory species breeding on the Missouri River, USA. We monitored 2507 piping plover Charadrius melodus nests and 3245 chicks as well as 1060 least tern Sternula antillarum nests and 1374 chicks on Lake Sakakawea, the Garrison River Reach and the Gavins Point Reach for varying years between 2007 and 2016. Piping plover nest and chick survival improved with the presence and abundance of least terns, but least terns only benefited from piping plover presence for certain study areas and breeding stages. Piping plover nest survival was also improved by the presence and abundance of conspecifics on the Garrison River Reach and was negatively influenced by conspecific presence on Lake Sakakawea. Least tern chick survival improved with the presence of other least terns only on the Gavins Point Reach. Ultimately, the heterospecific breeding association between plovers and terns is mutualistic but asymmetric and is moderated by habitat, abundance of conspecifics and breeding stage. Our results highlight that spatiotemporal variation in the interactions among individuals breeding in groups precludes simple generalizations and suggests that management focused on one species may restrict benefits to that focal species if nest site requirements for heterospecifics are not also included.

Dispersal distance is driven by habitat availability and reproductive success in Northern Great Plains piping plovers

“…Conspecific densities during the breeding season can confer varied impacts on plover reproduction, including rates of double-brooding [ 30 ] and nest survival [ 69 ]. While density dependent dispersal is thought to be due to limitations in available habitat, we did not detect a relationship between dispersal distances and densities at the hatching, previous, or settling sites for either age class.…”

“…Adult density was calculated as twice the number of nests found on a segment corrected for known renesting probabilities [ 68 ] during that breeding season divided by the length of that segment because conspecific abundance can influence nest survival [ 69 ]. Because nest monitoring efforts varied among years of study, we estimated chick density as the number of chicks hatched from nests on each segment in each year with a series of assumptions.…”

Implications of habitat‐driven survival and dispersal on recruitment in a spatially structured piping plover population

“…Pre‐fledging mortality in piping plovers has been linked to predation pressure (Cohen et al, 2009), but generally, the results of other studies and ours do not support strong density dependence (Anteau et al, 2022; Anteau, Wiltermuth, Sherfy, Shaffer, & Pearse, 2014; Cohen et al, 2009). Pre‐fledging chick survival in the NGP is also affected by recent flooding events that create habitat and by the presence of heterospecifics that mob predators, which may mask any detectible annual effects (Anteau et al, 2019; Hunt et al, 2018; Swift, Anteau, Roche, et al, 2020). It is equally likely that our ability to detect relationships between survival and factors on breeding areas was obscured by broader‐scale factors during the post‐fledging period, such as events (e.g., extreme storms and harmful algal blooms) occurring on nonbreeding areas (Ellis et al, 2021).…”

“…If a nest was presumed successful due to alternate pieces of evidence (e.g., chick droppings and pipping fragments), we used the maximum observed clutch size corrected for the mean hatching rate of eggs (78.5%; Swift et al, 2021a) calculated from 129 successful nests closely monitored from 2014 to 2015. Adult density was calculated as twice the number of nests found on that segment corrected for known renesting probabilities (Swift, Anteau, Ring, et al, 2020) during that breeding season divided by the length of that segment, because conspecific abundance can influence nest survival (Swift, Anteau, Roche, et al, 2020). Conspecific densities were standardized within each management unit due to the differences in segment length measurement strategies.…”

Experimental evaluation of predator exclosures on nest, chick, and adult survival of piping plovers

“…We banded many adults during previous studies (Anteau et al 2019; Swift et al 2020 a , b ), with a USGS metal band and unique alpha‐numeric engraved flag. We trapped unbanded adults on nests during incubation using either a modified remote‐controlled walk‐in trap or bow‐net (Anteau et al 2019).…”