Still no evidence for disruption of global patterns of nest predation in shorebirds
Authors: Bulla Martin , Valcu Mihai , Kempenaers Bart 
Published: February 2021

Many shorebird species are rapidly declining (Piersmaet al. 2016; Munro 2017; Studdset al. 2017), but it is not always clear why. Deteriorating and disappearing habitat, e.g. due to intensive agriculture (Donalet al. 2001; Kentieet al. 2013; Kentieet al. 2018), river regulation (Nebelet al. 2008) or mudflat reclamation (Maet al. 2014; Larson 2017), and hunting (Reedet al. 2018; Gallo-Cajiaoet al. 2020) are some of the documented causes. A recent study suggests yet another possible cause of shorebird decline: a global increase in nest predation (Kubelkaet al. 2018). The authors compiled an impressive dataset on patterns of nest predation in shorebirds and their analyses suggest that global patterns of nest predation have been disrupted by climate change, particularly in the Arctic. They go as far as to conclude that the Arctic might have become an ecological trap (Kubelkaet al. 2018). Because these findings might have far-reaching consequences for conservation and related political decisions, we scrutinized the study and concluded that the main conclusions of Kubelkaet al. (2018) are invalid (Bullaet al. 2019a). The authors then responded by reaffirming their conclusions (Kubelkaet al. 2019b).

Here, we evaluate some of Kubelkaet al.’s (2019b) responses, including their recent erratum (2020), and show that the main concerns about the original study still hold. Specifically, (1) we reaffirm that Kubelkaet al.’s (2018) original findings are confounded by study site. Hence, their conclusions are over-confident because of pseudo-replication. (2) We reiterate that there is no statistical support for the assertion that predation rate has changed in a different way in the Arctic compared to other regions. The relevant test is an interaction between a measure of time (year or period) and a measure of geography (e.g., Arctic vs the rest of the world). The effect of such an interaction is weak, uncertain and statistically non-significant, which undermines Kubelkaet al.’s (2018) key conclusion. (3) We further confirm that the suggested general increase in predation rates over time is at best a weak and uncertain trend. The most parsimonious hypothesis for the described results is that the temporal changes in predation rate are an artefact of temporal changes in methodology and data quality. Using only high-quality data, i.e. directly calculated predation rates, reveals no overall temporal trend in predation rate. Below we elaborate in detail on each of these points.

We conclude that (i) there is no evidence whatsoever that the pattern in the Arctic is different from that in the rest of the world and (ii) there is no solid evidence for an increase in predation rate over time. While we commend Kubelkaet al. for compiling and exploring the data, we posit that the data underlying their study, and perhaps all currently available data, are not sufficient (or of sufficient quality) to test their main hypotheses. We call for standardized and consistent data collection protocols and experimental validation of current methods for estimating nesting success.