Abstract
Rainfall in tropical semi-arid areas may act as a reliable cue for timing bird reproduction, since it precedes future food supply. With this in mind, we set-up a study to test the reproductive response of insectivorous bird to arthropod abundance and rainfall patterns. Sampling occurred in a seasonally dry Neotropical forest, in north-eastern Brazil, between October, 2015 and October 2016, at 14-day intervals. We used brood patch to assess reproductive periodicity of insectivorous birds (eight species, 475 captures, 121 patch records). We sampled arthropods to quantify abundance, using biomass and number of individuals (1755 individuals, 15 Orders). Rainfall temporal distribution was analyzed using daily precipitation data. We used a cross-correlation function to test for correlation and time-lags between the covariates under study. Both the number of reproductively-active birds and arthropod abundance were higher in time periods close to the rainy season. Increase in arthropod biomass in the aerial stratum preceded the period of greatest rainfall by one (14 days, r = 0.44) to three sampling periods (0.47). In contrast, the highest proportion of individuals with brood patches occurred after the main rainfall peak, with the strongest relationship occurring after two (0.52) to four (0.50) time lags. Finally, the proportion of individuals with brood patches was positively correlated with aerial stratum arthropod biomass when five time lags were considered (0.55). Our results support the hypothesis of a temporal process involving rainfall, arthropods and reproduction of insectivorous birds in the wet/dry tropics. However, rainfall did not appear to act as a cue for the timing of reproduction, since records indicated higher arthropod biomass before the main rainfall peak. At least occasionally in the study area, insectivorous bird reproduction peaks after food abundance.
Highlights
In tropical seasonally dry areas there is widespread evidence of links between rainfall, bird breeding phenology and clutch size (Immelmann 1971, Zann et al 1995, Ahumada 2001, Morrison and Bolger 2002, Cox et al 2013, Cavalcanti et al 2016). Such relationships are attributed to the influence of rainfall on both primary productivity and the abundance of arthropods and fruits (Poulin et al 1992, Lloyd 1999, Schloss et al 1999, Illera and Díaz 2006, Williams and Middleton 2008), and linked to the role such resources have as important sources of energy to help birds meet the demands of reproduction (Poulin et al 1993)
We explore the relation among rainfall-food-reproduction in an insectivorous bird assemblage in a seasonally dry tropical forest in north-eastern South America (Miles et al 2006, Pennington et al 2009)
A relationship between timing of Caatinga dry forest bird reproduction and the rainy season has been reported by other studies (Cavalcanti et al 2016, Araujo et al 2017)
Summary
In tropical seasonally dry areas there is widespread evidence of links between rainfall, bird breeding phenology and clutch size (Immelmann 1971, Zann et al 1995, Ahumada 2001, Morrison and Bolger 2002, Cox et al 2013, Cavalcanti et al 2016) Such relationships are attributed to the influence of rainfall on both primary productivity and the abundance of arthropods and fruits (Poulin et al 1992, Lloyd 1999, Schloss et al 1999, Illera and Díaz 2006, Williams and Middleton 2008), and linked to the role such resources have as important sources of energy to help birds meet the demands of reproduction (Poulin et al 1993). High winter bird mortality and high food productivity in the summer result in a food surplus conducive to feeding
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