No evidence for disruption of global patterns of nest predation in shorebirds

Abstract

†These authors formed the core team behind the Technical Comment. The remaining authors are listed alphabetically according to their first name. Affiliations located after Acknowledgements.Abstract Kubelka et al. (Science, 9 November 2018, p. 680-683) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims. Main textClimate change affects organisms in a variety of ways (1-4), including through changes in interactions between species. A recent study (5, referred to as "the Authors") reports that a specific type of trophic interaction, namely depredation of shorebird nests, increased globally over the past 70 years. The Authors state that their results are "consistent with climateinduced shifts in predator-prey relationships". They also claim that the historical perception of a latitudinal gradient in nest predation, with the highest rates in the tropics, "has been recently reversed in the Northern Hemisphere, most notably in the Arctic." They conclude that "the Arctic now represents an extensive ecological trap… for migrating birds, with a predicted negative impact on their global population dynamics". These conclusions have far-reaching implications, for evolutionary and population ecology, and for shorebird conservation and related policy decisions (6). Therefore, such claims require robust evidence, strongly supported by the data. Here we dispute this evidence.First, the Authors graphically show non-linear, spatio-temporal variation in predation rates (their Fig. 2AB and 3), and suggest that in recent years, predation has strongly increased in North temperate and especially Arctic regions, but less so in other areas. However, they only statistically test for linear changes in predation rates over time for all regions combined, and for each geographical region (their Table S2) or period (before-and after-2000; their Table S6) separately. To substantiate their conclusions, the Authors should have presented statistical evidence for an interaction between region/latitude and year/period on predation rate. Moreover, their analyses control for spatial auto-correlation, but failed to model nonindependence of data from the same site (pseudo-replication).Using the Authors' data, we ran a set of mixed-effect models, structurally reflecting their results depicted in their Fig. 2AB and 3, but including location as a random factor (Table 1, (7)). These analyses show (a) that much of the variation in nest predation rate is explained by study site (>60%, compared to species: <5%), implying a reduced effective sample size, (b) that all regions -except the South temperate -show similar predation rates, and (c) that nest predation rates increase over time similarly across all geographical areas (Fig. 1A-F). Linear models without interaction terms are much better supported than non-linear ...

Horseshoe crab egg availability for shorebirds in Delaware Bay: Dramatic reduction after unregulated horseshoe crab harvest and limited recovery after 20 years of management

“…Given this broad pattern, it is plausible that trajectories of shorebird populations stopping over in the bay are governed by factors beyond conditions encountered in the Delaware Bay. For example, one hypothesis concerns Arctic climate change altering patterns of reproductive output but to date, no clear pattern linking shorebird declines to Arctic breeding conditions has emerged (Weiser et al, 2018; Bulla et al, 2019). Shorebird population declines instead have been linked to adult survival (Weiser et al, 2020), with conditions that reduce survival typically encountered away from breeding sites (Weiser et al, 2017) during migration, stopover and wintering periods (Murray et al, 2018).…”

“…More than half of North America's shorebird species are considered to be of high conservation concern due to unabated threats and population declines (U.S. Shorebird Conservation Partnership, 2014;Hope et al, 2019). Given this broad pattern, it is plausible that trajectories (Weiser et al, 2018;Bulla et al, 2019). Shorebird population declines instead have been linked to adult survival (Weiser et al, 2020), with conditions that reduce survival typically encountered away from breeding sites (Weiser et al, 2017) during migration, stopover and wintering periods (Murray et al, 2018).…”

Trends in breeding performance in wader populations at Zackenberg, high Arctic Greenland, in relation to environmental drivers 1996–2018

“…Nor did we find any correlations between nesting data and year to year variability in our fox or lemming measures (but see below), which is similar to findings by Machín et al (2019) in sub-Arctic Sweden. Increased nest predation particularly in the Arctic has been postulated by Kubelka et al (2018) but questioned by Bulla et al (2019) while still maintained by Kubelka et al (2019) and refused by Bulla et al (2021). We have little to add to this discussion, since we are not able to distinguish between the effects of the apparent increased fox activity and the effects of our own activities at nests.…”

Anthropogenic impacts on the demographics of Arctic-breeding birds

“…Kubelka et al (2018) suggested that increases in Arctic wader nest predation are consistent with climate-induced changes to traditional predator-prey relationships; in particular disrupted lemming cycles and the behaviour and distribution of nest predators. However, Bulla et al (2019) subsequently disputed that nest predation rates have been disrupted due to climate change. Nonetheless, the indirect impact of disrupted lemming population cycles on Arctic-breeding birds was discussed in several earlier articles.…”