Comment on “Global pattern of nest predation is disrupted by climate change in shorebirds”

Abstract

Kubelka et al. (Reports, 9 November 2018, p. 680) 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.

Response to Comment on “Global pattern of nest predation is disrupted by climate change in shorebirds”

“…Taken together, these findings provide further evidence that the global pattern of nest predation was disrupted in shorebirds, and this conclusion remains unaffected by the concerns raised by Bulla et al (2). The key results of (1) are straightforward, supported by simple models and data: There is a strong temporal increase in nest predation rates at a global scale, with significant spatial variation.…”

“…In our study (1) we showed significant increases in daily nest predation rate in ground-nesting shorebirds that were especially strong in the Arctic. Bulla et al (2) raise four concerns about our findings. Here, we highlight statistical and methodological problems in Bulla et al's analyses.…”

“…We fitted the simplest model [log(DPR + 0.01) as a linear function of latitude and year]; both latitude and year are highly statistically significant. This is a simpler model than any used by Bulla et al(2), but notably has a lower Akaike information criterion (AIC) than the models they considered. Note that although the model does not include an interaction term on the log scale, the lines diverge on the arithmetic scale, indicating geographically divergent outcomes.…”

“…2) The simulations performed by Bulla et al include observation times (B) from 0.1 to 0.9 [figure 1H in (2)] with the artifactual increases in predation rate for historic data when B is very low (0.1 to 0.5). However, B should in principle vary from 0.5 of the incubation and egg-laying period in studies with random nest search to approximately 0.9 when all nests are found during the egg-laying period as a result of intensive research (8,11).…”

Status and trends of tundra birds across the circumpolar Arctic

“…Senner et al 2014;but see Duijns et al 2017;). Reproductive success of Arctic tundra waders is highly variable in space and time for many reasons, for example increasing with latitude (McKinnon et al 2010; but see Bulla et al 2019), or varying with snow conditions, weather, or variation in predator abundance and their preferred small mammal prey (reviewed in Meltofte et al 2007). Changing environmental conditions in the Arctic could help to explain why declines exist in some species but not others in flyways where staging sites have not declined radically in quality in recent years, such as in the East Atlantic portions of the African-Eurasian Flyway.…”