Parâmetros populacionais e reprodutivos de aves granívoras na Caatinga: estratégias de vida em um ambiente tropical sazonalmente seco

Abstract

The establishment of patterns that explain latitudinal variations in avian life history is based on data from tropical rainforests, and there are gaps regarding the evolution of their traits in seasonal tropical environments. The strong seasonality of these environments is related to the rainfall regime, with annual droughts seasons. In addition, they have unpredictable climatic variation, exhibiting cycles with prolonged dry periods. As consequence, they limit the availability of food, shelter and nesting sites, altering the dynamics of bird populations. The effects of these periods reflect what is to come in a scenario of global climate change, where is foreseen the increase of shorter rainy seasons. Thus, it is important to understand the strategies of bird populations to keep up with seasonality, and how they respond to severely dry periods, especially granivorous. The Caatinga is an example of a tropical seasonally dry ecosystem. This domain presents a variable and stressful rainfall regime, where in many regions annual rainfall does not exceed 500 mm. Therefore, the aim of this thesis was to estimate population and reproductive parameters of granivorous birds in a Caatinga area, during and after a severely dry period. We developed the study at the Estação Ecológica do Seridó, city of Serra Negra do Norte, RN, Brazil. The thesis is structured in three chapters. In Chapter 1, we estimated detection and survival rates of the passerine Grassland Sparrow (Ammodramus humeralis). We evaluate the hypotheses that apparent survival would be lower than that described for tropical rainforests, influenced by seasonality and negatively affected by the prolonged dry period. To analyze the data, we used Huggins' robust design model in the MARK program. Contrasting our hypotheses, the best fit model considered apparent survival as constant, and the annual estimates among those observed in rain forests. We believe that the population studied here was able to maintain a constant survival, even in the face of a period where resources were severely scarce, because they did not reproduce. Since reproduction involves an energy cost, not reproducing compensates the waste that reduces survival rates. In chapter 2, we estimated detection rates and abundance of Plain-breasted Ground-dove (Columbina minuta) and Picui Dove (Columbina picui) in two different physiognomies (shrubby and arboreal). We evaluated the hypothesis that the density is higher in the shrubby physiognomy, that the species are more abundant during the wet season, and that they are able to perform regional movements. For analyzes, we developed Huggins’ closed population models in MARK program. The results corroborate our three hypotheses. The population size suggested greater abundance in shrubland and during the wet season. Recoveries of C. minuta in other Caatinga localities, combined with low capture and recapture rates, and low fidelity to the sample areas, indicate that nomadism can be the main strategy adopted by this species to maintain its populations in face of the climatic unpredictability of the Caatinga. In chapter 3, we describe reproductive characteristics (egg size and weight, incubation and nestling period, nest density and behavioral traits) of Ground-doves C. minuta and C. picui. We also estimated nest daily survival rates (TSD) assessing the hypothesis that it would be affected by environmental traits (plant support species, camouflage level or nest height), higher during nestling stage than egg stage, and the nest predation would be lower in these Columbidae than in species of other avian orders. We used the Mayfield method and developed nest survival models in the MARK program for data analysis. We verified that both species nest in several plant species at heights between 0 and 400 cm, and that only camouflage level was an important factor in TSD. The estimates were higher during the nestling phase, corroborating our hypothesis. Predation was the main cause of losses, however with rates similar to those observed for species of other orders and other environments. We believe that the present thesis contributes to a better understanding of the evolution of avian life history traits that inhabit seasonally dry environments in Tropical regions, since the existing pattern is predominantly based on rainforest data. In addition, it provides unpublished information about the natural history of birds inhabiting Caatinga (eg. egg size and weight, reproductive period duration, nest predation rates) and collaborates with the understanding of strategies adopted by granivorous species to maintain their populations in periods of severe resource scarcity (nomadism), which will become increasingly frequent in a climate change scenario.