Geographical variation and current knowledge on breeding patterns of Neotropical accipitrid raptors

Avian life-history studies are mostly restricted to the latitudinal paradigm of clutch-size variation, ignoring the value of trade-offs between the different parameters. One of these parameters is the breeding season length (therefore, BSL), considered to also present a latitudinal cline, increasing toward the tropics. Moreover, there is evidence that nesting seasons diverge latitudinally among closely-related taxa, but the perception of day-length variation by birds at lower latitudes has long been debated. Results from studies conducted in South America and through the Southern Hemisphere challenges BSL’s latitudinal paradigm. Most of these studies focus on passerine communities, overlooking larger species such as raptors, but it is essential to verify if patterns hold true across bird clades. Also, such knowledge about breeding biology is relevant for species’ management and conservation. I analyzed the occurrence of geographical variation in breeding parameters of Neotropical accipitrid raptors. In the first Chapter, motivated by the lack of a recent, comprehensive survey of the state-of-the-art spanning the entire Neotropics, I examined gaps of knowledge on these birds’ breeding biology. I compiled 457 references, produced since the last similar review (Bierregaard 1995), that reported breeding of 56 species. Although 66% of the evaluated species had an improvement on the state of knowledge, for seven species nests have not been described yet, and/or there is a complete absence of information about their breeding behavior. Among these, the former “Leucopternis clade” remains the most problematic case. I provide an update of current levels of knowledge about the breeding biology of Neotropical Accipitriformes, and present a list of 24 priority species for breeding biology studies, considering both information gaps and current conservation relevance. The review performed on Chapter 1 was the baseline and allowed the analyses made in Chapter 2, that used data of the buteonines clade, a diversified monophyletic group of accipitrid raptors, with relatively well-known breeding biology. In the second Chapter, I verified whether these raptors present patterns of geographical variation in breeding seasonality. I obtained 1541 nest records from 27 species of the Neotropical region, from literature and also 16 museum egg collections. Records were divided between samples (‘units’), among latitudinal ranges, according to phylogeny and relevant ecological and biogeographical traits, and also between ecoregions. Significant differences were found between estimates of initiation of the breeding season (IOB) from different latitudinal ranges: the means of southern tropical units differed from those of both northern tropical (ANOVA; Q = 5.987; P < 0.001) and southern temperate ones (Q = 6.731; P < 0.001). Estimates of IOB are also negatively correlated with latitude (r = -0.667; r2 = 0.445; P = 0.018). Values of BSL varied significantly less than those of IOB (a posteriori Fligner-Kileen tests for coefficients of variation), and I found no support for the prediction that breeding season lengths of populations of different species within a same latitudinal range will significantly diverge from other ranges’. Also, migrants and non-migrant units had no significantly different BSLs, and no kind of “island effect” occured with BSLs of units on islands, in any level of isolation. Neotropical buteonine’s breeding seasons start earlier than those of passerines, and probably earlier than other accipitrids, either in the same range or elsewhere. There is a pattern of latitudinal clines in the IOBs as their seasons start up to 100 days before vernal equinox in both tropical ranges, but later on the temperate range. These findings suggest that day-length stimuli are the main proximate clues determining the onset of their breeding seasons. I also suggest that unpredictability on climate do not necessarily select for longer breeding seasons in birds, and demonstrate that among Neotropical buteonines, shortdistance migrants have BSLs very similar to those of non-migrants, indicating no substantial time-constraints for their breeding activities. Reproductive and/or evolutionary isolation of insular populations alone may not select for increasing divergence in breeding parameters, relative to mainland populations. Due to the scarcity of ecological and behavioral data for most of these species, particularly in northern and central South America, I highlight the relevance of conducting detailed studies with different populations, and also how scrutiny of oological collections could fill some gaps of knowledge. I also demonstrate how, even with data far from ideal, research can provide new evidence and put forward testable hypotheses.