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.