Climate, crypsis and Gloger’s rule in a large family of tropical passerine birds (Furnariidae)

Abstract

49Gloger's rule predicts endothermic animals should have darker colors under warm and 50 rainy climates, but empirical studies have typically found that animals tend to be darker under 51 cool and rainy climates. Moreover, Gloger's rule has rarely been tested jointly with the 52 prediction that animals occupying dark habitats should have darker colors to enhance crypsis. 53 We aimed to disentangle the effects of climate and light environments (habitat type) as correlates 54 of plumage brightness in a large Neotropical passerine family. We found that cooler and rainier 55 climates are associated with darker plumage, even after accounting for habitat types, and that 56 darker habitats are associated with darker plumage, even after accounting climate. There was an 57 important interaction between precipitation and temperature, whereby the negative effect of 58 temperature on brightness becomes stronger under cooler temperatures. Climate and light 59 environments have separate but complementary effects in driving macroevolutionary patterns of 60 plumage color variation in birds. 61 62 63 64 65 66 67 68 69 70 71 4Ecogeographic rules describe correlations between organismal phenotypes and features 72 of their environment. Their repeated observation across taxa and space is prima facie evidence 73 that they are driven by common selective pressures (Mayr 1963, James 1991, VanderWerf 2011. 74Gloger's rule (Gloger 1833, Rensch 1929) is a longstanding ecogeographic rule describing a 75 correlation between the colors of mammals and birds and the climatic conditions they occupy. 76