Old growth and secondary forest site occupancy by nocturnal birds in a Neotropical landscape

Abstract

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.