High rates of old growth (OG) forest destruction and difficult farming conditions result in increasing cover of secondary forests (SF) in the Amazon. In this setting, it is opportune to ask which animals use newly available SF and which stay restricted to OG. This study presents a comparison of SF and OG site occupancy by nocturnal birds in terra firme forests of the Amazon Guianan shield, north of Manaus, Brazil. We tested species-specific occupancy predictions for two owls (Lophostrix cristata/Glaucidium hardyi), two potoos (Nyctibius leucopterus/Nyctibius griseus) and two nightjars (Caprimulgus nigrescens/Nyctidromus albicollis). For each pair, we predicted that one species would have higher occupancy in OG while the other would either be indifferent to forest type or favor SF sites. Data were collected in 30 OG and 24 SF sites with monthly samples from December 2007 to December 2008. Our analytic approach accounts for the possibility of detection failure and for spatial autocorrelation in occupancy, thus leading to strong inferences about changes in occupancy between forest types and between species. Nocturnal bird richness and community composition were indistinguishable between OG and SF sites. Owls were relatively indifferent to forest type. Potoos followed the a priori predictions, and one of the nightjars (C. nigrescens) favored SF instead of OG as predicted. Only one species, Nyctib. leucopterus, clearly favored OG. The landscape context of our SF study sites, surrounded by a vast expanse of continuous OG forest, partially explains the resemblance between SF and OG fauna but leaves unexplained the higher occupancy for SF than OG sites for several study species. The causal explanation of high SF occupancy remains an open question, but the result itself motivates further comparisons for other groups, as well as recognition of the conservation potential of SF.
Aim To offer a test of expert knowledge about rarity of twenty Amazon forest bird species following an approach that equates rarity with low site occupancy and formally accounts for imperfect species detection. We define ten pairs of closely related species, each pair with one hypothetically common and one hypothetically rare species. Our null hypothesis is that members of each pair have similar occupancy, with hypothesized differences due to detection errors alone.Location A 1000-ha plot of primary rainforest in the central Brazilian Amazon.Methods We visited each of 55 sampling sites multiple times per season for three field seasons and estimated the probability of site occupancy by each species following a maximum likelihood state-space approach that also estimates the probability that a species is present yet undetected at a site. To maximize detection and account for its variation, we employed three different sampling techniques while systematically training and testing observer's ability to recognize species.Results Occupancy estimates agree with expert predictions in all but two species pairs and show no evidence of clear temporal variation in occupancy between sampling seasons. Detection probability had a positive relation with observer ability, a strong relation to time of day across species, and a strong relation with the use of playback for some species. Detection with point counts and with autonomous recorders varied between species pairs. Main conclusions We reject the null hypothesis of equal occupancy within pairs, concluding that expert knowledge on species rarity is useful and worth eliciting. Our results replace qualitative ratings of rarity with statistical estimates of occupancy, establishing a reliable baseline for future comparisons. Besides illustrating the relevance of expert knowledge, this application to Amazonian birds illustrates a flexible approach that can be used for testing knowledge about rarity for a variety of species groups and spatial scales.
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