RESUMO
Insectivores of the tropical rainforest floor are consistently among the most vulnerable birds to forest clearing and fragmentation. Several hypotheses attempt to explain this pattern, including sensitivity to extreme microclimates found near forest borders, particularly brighter and warmer conditions. Importantly, this "microclimate hypothesis" has additional implications for intact forest under global climate change that could be evaluated through direct assessment of the light and temperature environment of terrestrial insectivores. In this study, we harness novel technology to directly quantify the light and thermal niches of 10 species of terrestrial insectivores in undisturbed Amazonian rainforest. Loggers placed on birds (N = 33) and their environment (N = 9) recorded nearly continuous microclimate data from 2017 to 2019, amassing >5 million measurements. We found that midday light intensity in tree fall gaps (~39,000 lux) was >40 times higher than at the ground level of forest interior (950 lux). Light intensity registered by sensors placed on birds averaged 17.4 (range 3.9-41.5) lux, with species using only 4.3% (0.9%-10.4%) of available light on the forest floor. Birds therefore selected very dark microhabitats-the light environment was >2200 times brighter in tree fall gaps. Bird thermal niche was a function of ambient temperature as well as body temperature, which averaged >40.5°C but varied among species. Forest floor temperature peaked daily at 27.0°C, whereas bird loggers averaged 35.1°C (34.5-35.7°C) at midday. The antpitta Myrmothera campanisona and the antthrush Formicarius colma used thermal conditions closest to their body temperatures, whereas leaftossers (Sclerurus spp.) and Myrmornis torquata occupied relatively cool microclimates. We found no general link between abundance trends and variation in species-specific light and thermal niches. However, all species occupied markedly dim and cool microclimates. Because such conditions are rare outside the interior of primary forest, these results support the microclimate hypothesis in disturbed landscapes. Moreover, strong avoidance of conditions that are becoming more common under climate change highlights the vulnerability of terrestrial insectivores even in the absence of disturbance and may be the reason for enigmatic declines in Amazonia and elsewhere.
Assuntos
Aves , Floresta Úmida , Animais , Ecossistema , Florestas , Microclima , ÁrvoresRESUMO
In order to evaluate the efficiency of different mammalian survey methods, we compared traditional sampling techniques (use of camera-traps on roads and artificial trails, track censuses, and direct field visualization) with an alternative sampling design (camera-traps positioned in natural areas such as natural trails and shelters). We conducted the study in a deciduous Atlantic-Forest park in southern Brazil, and additionally compared our results with a previous intensive study carried out in the same area. Our considerably smaller sampling effort (example: 336 trap.day for our camera-traps versus 2,154 trap.day for the earlier study) registered the presence of 85% of the local known species, with camera-traps being 68% efficient. Moreover, shelter camera-traps revealed a different species composition regarding most of other sampling methods. This sampling strategy involving natural forest sites was therefore able to effectively optimize the chances of evaluating species composition in a shorter period, especially with respect to lower-density and cryptic species, as well as to detect species that avoid open, disturbed sites such as roads and man-made forest trails.
A fim de avaliar a eficiência de vários métodos de levantamento de mamíferos, comparamos as técnicas de amostragem tradicionais (uso de armadilhas fotográficas nas estradas e trilhas artificiais, procura por pegadas, e visualização direta em campo) com um delineamento amostral alternativo (armadilhas fotográficas posicionados em áreas naturais, tais como carreiros naturais e abrigos). Realizamos o estudo em uma floresta estacional decidual no sul do Brasil, e comparamos nossos resultados com um estudo anterior intensivo realizado na mesma área. Nosso esforço amostral consideravelmente menor (exemplo: 336 armadilhas.dia para armadilhas fotográficas contra 2.154 armadilhas.dia no estudo anterior) registrou a presença de 85% das espécies previamente conhecidas para a área, com armadilhas fotográficas tendo 68% de eficiência. Além disso, as armadilhas fotográficas posicionadas em abrigos revelaram uma composição diferente de mamíferos em comparação com a maioria dos outros métodos de amostragem. Esta estratégia de amostragem que envolve locais de floresta natural foi, portanto, capaz de efetivamente otimizar as chances de avaliar a riqueza de espécies em um curto período, especialmente com relação a espécies crípticas e/ou de menor densidade, bem como detectar as espécies que evitam áreas abertas, como estradas e trilhas abertas pelo homem na floresta.
RESUMO
In order to evaluate the efficiency of different mammalian survey methods, we compared traditional sampling techniques (use of camera-traps on roads and artificial trails, track censuses, and direct field visualization) with an alternative sampling design (camera-traps positioned in natural areas such as natural trails and shelters). We conducted the study in a deciduous Atlantic-Forest park in southern Brazil, and additionally compared our results with a previous intensive study carried out in the same area. Our considerably smaller sampling effort (example: 336 trap.day for our camera-traps versus 2,154 trap.day for the earlier study) registered the presence of 85% of the local known species, with camera-traps being 68% efficient. Moreover, shelter camera-traps revealed a different species composition regarding most of other sampling methods. This sampling strategy involving natural forest sites was therefore able to effectively optimize the chances of evaluating species composition in a shorter period, especially with respect to lower-density and cryptic species, as well as to detect species that avoid open, disturbed sites such as roads and man-made forest trails.
A fim de avaliar a eficiência de vários métodos de levantamento de mamíferos, comparamos as técnicas de amostragem tradicionais (uso de armadilhas fotográficas nas estradas e trilhas artificiais, procura por pegadas, e visualização direta em campo) com um delineamento amostral alternativo (armadilhas fotográficas posicionados em áreas naturais, tais como carreiros naturais e abrigos). Realizamos o estudo em uma floresta estacional decidual no sul do Brasil, e comparamos nossos resultados com um estudo anterior intensivo realizado na mesma área. Nosso esforço amostral consideravelmente menor (exemplo: 336 armadilhas.dia para armadilhas fotográficas contra 2.154 armadilhas.dia no estudo anterior) registrou a presença de 85% das espécies previamente conhecidas para a área, com armadilhas fotográficas tendo 68% de eficiência. Além disso, as armadilhas fotográficas posicionadas em abrigos revelaram uma composição diferente de mamíferos em comparação com a maioria dos outros métodos de amostragem. Esta estratégia de amostragem que envolve locais de floresta natural foi, portanto, capaz de efetivamente otimizar as chances de avaliar a riqueza de espécies em um curto período, especialmente com relação a espécies crípticas e/ou de menor densidade, bem como detectar as espécies que evitam áreas abertas, como estradas e trilhas abertas pelo homem na floresta.