Community studied
The data were collected from a 40-ha patch of native forest located in the centre of Santa Fe Province (60° 55’ W, 31° 23’ S), Argentina, representing relicts of the biogeographic province ‘El Espinal’. The climate in the region is Pampean Temperate, with an average annual temperature of 18 °C (mean minimum= 12 °C; mean maximum= 23 °C) (www.climayagua.inta.gov.ar). These forests are breeding grounds for around 100 bird species, mostly Passeriformes (de la Peña, 2018). Because trees of El Espinal are not high, accessing the vast majority of bird nests of the community becomes feasible. At the study area, more than 20 species have been found to be parasitized by ‘P. torquansc. A.’ larvae (Antoniazzi et al. 2011; Manzoli et al. 2013), but the Great Kiskadee is by far the preferred host, with prevalences over 3 times higher than those of the second most used host (Manzoli et al, 2013). Among the most frequently parasitized alternative hosts are the Greater Thornbird and the Little Thornbird (Antoniazzi et al, 2011). These three species were selected for this study, due to their abundance, the prevalence of infection by the parasite, and because there are prior data on resistance, tolerance and parasite success (Manzoli et al. 2018). Nonetheless, data on parasite occurrence was weekly obtained from all hosts present in the area. Given the established differences in host competence for the three focal host species, they may be categorised as the ‘optimal host’ (the Great Kiskadee; it survives and does not resist), the ‘good alternative’ (the Greater Thornbird; resists poorly and high burdens cause death) and the ‘bad alternative’ (the Little Thornbird; resists efficiently and moderate to high burdens cause death).
The breeding season of these host species ranges from October to March. In this study we analysed data from 8 breeding seasons, corresponding to the dates 2006/2007, 2007/2008, 2008/2009, 2009/2010, 2012/2013, 2013/2014, 2014/2015, 2015/2016.