Historia natural, demografia, viabilidade populacional e conservacaode Asthenes luizae (Furnariidae), ave endemica dos campos rupestresda Cadeia do Espinhaco, Minas Gerais

Abstract

This study aimed to contribute to the conservation and understanding of the natural history and ecology of Asthenes luizae (Furnariidae), a little-known bird confined to rocky outcrops habitats of the campos rupestres of the Espinhaco Range in the state of Minas Gerais, Brazil. Over six years I monitored a population in Serra do Cipo to study the nesting habits, reproductive success and demography, focusing on the impact of one of the most mentioned threat to the species: the broodparasitism by the Shiny Cowbird Molothrus bonariensis. Nesting habits were comparatively analyzed with the related species of Synallaxini, investigating the evolutionary history of nest features. I used the available data regarding its life history and ecology to perform a PopulationViability Analysis (PVA), inferring its risk of global extinction and assessing its threatened status according to the IUCN categories and criteria. The main results related to the nesting were: their closed nests (n = 81) do not have entrance tunnels or tubes; are composed mainly of sticks, but also other vegetable, mineral and animal materials; three nest layers can be distinguished according to the composition; the inner lining covers the entire nest interior; and nest sites are not restricted to the plant species Vellozia nivea (Velloziaceae), as previously supposed. I recorded a wide range of nest sites, mainly at a low height (mean = 33.4 cm), mostly (95%) in plants with diverse architectures (at least 29 species, 82% endemic to Espinhaco), but also on rocks. Stick nests wereprevalent in Synallaxini clade, but not among Asthenes, and I suggest that it was the ancestral state of the latter. While tunnels were recorded in most stick-nesters, any confirmed evidence that tubes occurs within Asthenes was found and it appears to be restricted to the clade containing Pseudasthenes and closest relatives. The various components of reproductive success were low, with the nest success (10%) being one of the lowest among Neotropical passerines. Partial losses of eggs and nestlings also contributed to the low productivity rates (0.12 fledglings/nest; 1.22 fledglings/successful nest) and fecundity (c. 0.58 fledglings/female). The main cause of nest failure was the brood parasitism by Shiny Cowbirds (56% of failures), that occurred with high frequency (60%) and intensity (2,9 parasites/nest). Once parasitized, the chance of a nest produce a host fledgling is zero. Predation was the second major cause of nest failure for A. luizae (33% of failures), but was the main obstacle to a nest produce fledglings, host or parasite (86% of total failures). The hypothetical elimination of brood parasitism indicated that it could be nearly duplicate the rate of nest success (18%), nest productivity (0.22 fledglings/nest) and female fecundity (c. 0.98 fledglings/female). The breeding season was extremely long, occupying 67% of the year, which can be one way to the host to escape from brood parasitism. The monitoring of marked individuals (n = 37) and territories (n = 22) revealed a strong population decline between 2009 and 2015. Since the beginning of the study, there was a shortage of females, reflecting in the biased sex ratio (M:F = 2.7) and low proportion of paired individuals (47%). The adult annual x survival was relatively high (72%), but the annual survival of adult females (46%) and juveniles (29%) were low, although estimated with greater uncertainty. Territory switches were rare, suggesting low migration rates. The increase in the number of vacant territories (up to 61%) indicates that there was low recruitment by birth or immigration. The average density of adults was 0.08 individuals/ha of study area and 0.17 individuals/ha of rocky outcrops, but the density of mature individuals (paired) was much lower (0.03 and 0.07, respectively). The species' global population size was projected as c. 21,800 mature individuals, unevenly distributed among the three main blocks of the Espinhaco Range mountains (700 in the north, 1,900 in central and 19,800 in the south). The AVP projected very high extinction probabilities for the population in the Serra do Cipo National Park, indicating that it is inviable over 100 years if kept current conditions, even under the most optimistic models (time to extinction = 11-31 years). Alternative scenarios indicated that the elimination of the effects of inbreeding depression did not cause significant impacts, whileeliminating brood parasitism effects increased the population growth rates at 12-50% and delayed the time of extinction in 2-31 years. However, it did not ensure the population viability. Demographic perturbation analysis (elasticity and sensitivity) indicated that mortality of adult females was the parameter whose variation cause greatest changes in the population growth rate and the mean time to extinction. However, among the perturbation levels employed, only the 50%reduction in juvenile mortality under the optimistic model would produce viable populations. Populations equivalent to the global population size were also nonviable, extincting within 18-54 years. However, it would be viable under the optimistic model in the absence of brood parasitism.The risk of extinction is high enough to consider A. luizae threatened, at least in the Vulnerable category under the IUCN criterion E. Given the uncertainty of the efficiency and the complexity of a direct control of cowbirds, I suggest as a possible management strategy to control human impacts derived from fires and cattle, which have the potential to promote both the survival and reproduction of A. luizae, in addition to indirectly control the brood parasitism.