Protandria e seu impacto sobre a reprodução de uma ave migrante intra-tropical

Abstract

Introduction: Migratory birds annually face a costly journey during the breeding season. The arrival time in breeding grounds is associated with these costs and also with important consequences for individual fitness. Previous works show that the optimal moments of arrival in breeding ground vary according to sex, age and morphological traits, individuals who manage to advance the arrival date tend to have a greater investment and reproductive success in the season. However, little is known about the influence of the arrival date on intratropical migratory birds that are subjected to a different environment and therefore have a different pace of life than the temperate climate birds which most studies have been conducted. Methods: We monitored the arrival date of an intra-tropical migratory passerine, Lined Seedeater Sporophila lineola, to breeding grounds in southeastern Brazil, where a ringed population has been monitored since 2014. We conducted daily samplings in a predetermined path from 1 November 2019, till 13 February 2020, recording the arrival date, wing, tail and tarsus length, sex and the unique combination of colored rings of each bird observed. We use a generalized linear model to analyse the influence of morphological traits and a wilcoxon rank sum test to analyse the influence of age and sex on the arrival date. To assess the influence of arrival date on reproductive traits we looked for nests from November 2019 to March 2020. We used a generalized linear model to assess the influence of arrival date on assortative mating, reproductive success, number of breeding attempts and investment in broods on first attempt and throughout the full season. Results: We were able to determine the arrival date of 125 individuals and find 137 nests. Our results indicate that older males arrive before younger ones and that males, regardless of age, arrive before females (protandry). Individuals with longer tails and tarsus also arrived earlier, regardless of sex. The investment in each brood seems to be inversely correlated with the arrival date, however it is directly related to the start of the season and the number of reproductive attempts, which generated an increase in male fitness, for females the increase in fitness seems to be corelated to arrival date of her partners. Conclusion: The present work showed the first evidence of protandry and an age and phenotype-dependent arrival date for the Lined Seedeater. It also points out that early arrival increases the duration of the breeding season and allows for a strategy in which the reproductive investment is diluted in a greater number of breeding attempts.