Environmental variables determining the distribution of an avian parasite: the case of the Philornis torquans complex (Diptera: Muscidae) in South America

Philornis flies are the major cause of myasis in altricial nestlings of neotropical birds. Its impact ranges from subtle to lethal, being of major concern in endangered bird species with geographically-restricted, fragmented and small-sized populations. In spite of its relevance for bird conservation, there is little information about the environmental dimensions determining their geographical range. We identified for the first time the macro-environmental variables constraining the abiotic niche of the P. torquans complex in South America, and provided a model map of its potential distribution based on environmental suitability. We used maximum entropy to model the ecological niche of the P. torquans complex, and to determine the contributing scenopoetic variables. We applied most of the recommendations to produce robust ecological niche models: accounting for sampling bias and spatial autocorrelation; using an accessible area for model calibration; testing multiple combinations of model parameters; using multiple statistical criteria; using a number of model replicates to determine consistency and uncertainty in geographical predictions. We identified the minimum temperature of the coldest month as the most relevant variable, associated with the largest decrease in habitat suitability in Brazil and northern South America. Furthermore, the mean temperature of the warmest quarter limited suitability mostly along the Andean range. In addition, humidity and moisture are influential factors in most of Argentina, northern Chile and coastal Peru. The geographical projection of the niche model suggests that environments in most of central-eastern Argentina, and in a broad area in central Chile, are suitable for the presence of the P. torquans complex. Besides of contributing to the knowledge of the ecology of the genus, this study is of relevance as a tool for bird conservation and represents a good reference for future work on the distribution of this parasite genus.