Fluctuating Selection and Reproductive Flexibility Figure 2. Partial regression plots of the statistically significant predictors of avian divorce. Axes refer to multivariate residuals after correcting for phylogeny and the effects of other significant parameters in the model. Each data point represents one species and dotted lines depict linear trends in the relationships between variables. doi:10.1371/journal.pone.0032311.g002 constraints in environments where the onsets of breeding opportunities are easier to predict. Although our data suggest that the rates of infidelity and divorce are affected by temperature cycles, we find no evidence that they are affected by local variation in precipitation. This result suggests that the patterns we uncovered here may not be driven by changes in resource abundance, which are typically determined by rainfall (e.g., [67,68]). For example, our sample in the divorce dataset includes several seabirds whose breeding success can be directly affected by changes in temperature but not necessarily by the existence of resource pulses on land (because these species forage at sea). Alternatively, the lack of an effect of precipitation could simply reflect the unfortunate geographic bias in the availability of samples for infidelity and divorce. In particular, most studies on these behaviors have been conducted in temperate, boreal, and polar regions (see Figs. S3 and S4), where the patterns of precipitation are fairly predictable (compared to the arid and semi- arid tropics) and the main source of environmental uncertainty is the variation in temperature (see Fig. 2 in [8]). It could also be argued that our results are not a product of interspecific differences in exposure to ecological cross-overs, but rather due to intrinsic differences in cognitive ability. Given the positive association between environmental uncertainty and cognition [6,7,69], it is possible that species exposed to more variable and unpredictable conditions engage more often in divorce and infidelity because they are better able to assess the relative value of available reproductive options. As a preliminary test of this hypothesis, we used the residuals of a log-log regression of brain mass on body mass (i.e., relative brain size) as a proxy for relative cognitive ability (see Text S1 and [70,71]) and repeated our analysis on the subset of species for which brain size data are available in the literature (Infidelity: N = 101; Divorce: N = 66, see Table S1). However, we found no evidence of an effect of relative brain size on infidelity (PGLS: t = 0.847, df = 97, P = 0.399), or divorce (PGLS: t = 20.185, df = 59, P = 0.854) and therefore, we conclude that differences in cognitive ability are unlikely to explain all aspects of the association between climatic tolerances and these behaviors. PLoS ONE | www.plosone.org 5 February 2012 | Volume 7 | Issue 2 | e32311