História de vida de asthenes luizae: biologia reprodutiva,sucesso reprodutivo e o impacto de molothrus bonariensis em uma ave ameaçada e endêmica dos campos rupestres dacadeia do espinhaço

Abstract

Life-history traits of the Cipó Canastero Asthenes luizae: breeding biology, reproductive success and the impact of the cowbird Molothrus bonariensis at a threatened and endemic bird to campos rupestres of Espinhaço Range, Brazil. The Cipó Canastero, Asthenes luizae, is a threatened ovenbird endemic to campos rupestres (rocky grasslands) ofEspinhaço Range from Minas Gerais state, Brazil. It´s natural history is poor-known. Between March 2009 and December 2010, we investigated by radio-telemetry several life history traits of these species in two study sites at Serra do Cipó, Minas Gerais state. We described the breeding biology, defined the reproductive success, and characterized thebrood parasitism system with the cowbird Molothrus bonariensis, of which is a host. Forty six nest were found, being 14 active. The nests were composed by a thick wall of mud and plant fragments, densely covered by sticks and lined by animal or vegetal soft material.The nests were closed and presents a lateral opening, preferentially oriented to northwest. The nests were diversely supported by 19 plant species, contradicting previous assumptions of specificity to Vellozia nivea (Velloziaceae). The fledging presented a distinctive plumage for about 3-4 months. Nest building, incubation and nestling feeding allshowed biparent care and long duration, of 21, 23 e 20 days, respectively. The young remained dependent by at least one month and left the natal territory around the third month after leave out the nest, performing a major dispersive movement at the onset of the next breeding season. The extended breeding season, from August to February, beganbefore the rainy and ended before the dry season, when starts the moult activity. Seven couples made up to three multiple brooding, but just one nest was successful. Canastero´s breeding success is one of the lowest at Neotropical region. The nest success computed by Mayfield method was 6,8%, and the apparent success was 9,1%. The offspring survivalrate (from egg to fledging) was 4,2 e 4,5%, by those two methods. The main cause of nest failure was brood parasitism (50,0%), followed by predation (33,3%), and nest desertion (16,7%); egg partial losses were also recorded. The annual productivity was 0,11 offspring/active nest, and 0,17 offspring/female. Total parasitism frequency was 53,9%,restricted to 35,2% of Canastero´s breeding season, and average parasitism intensity was 2,4 ± 1,7 eggs/nest. A short incubation provide to parasite an early hatch, causing the host nestling to death within a few days. The 'nest survival' rates, disregarding the contents, isslight higher in those parasitized (24,3%) than non parasitized nests (11,4%), revealing that the low survival of A. luizae in parasitized nests (0,03%) is due only to the presence of cowbird. The critical period of parasitism to the host was the nestling period. Low samplesdifficult the statistical investigation between the survival rates, what led us to confront the percentages verifying the potential extension of those differences. Raises the necessity to better investigate the Canastero´s reproductive success and other demographic parameters, allowing access the population viability and management options analysis forthese threatened species.