Study Area and Natural History
The study was conducted in Nahuel Huapi National Park and Llao Llao Municipal Reserve in northwestern Patagonia, Argentina. The climate in this region has a dry season in spring-summer and a humid season in autumn-winter, with 1800 mm of average annual precipitation and 9°C of average annual temperature. The forest is dominated by the evergreen southern beech (Nothofagus dombeyi) and cordilleran cypress (Austrocedrus chilensis ), with an understory layer dominated by the shrub Aristotelia chilensis and bamboo Chusquea culeou(Mermoz & Martín 1986). Currently the non-native ungulates red deer (Cervus elaphus ), dama deer (Dama dama ), and domestic cattle (Bos taurus ) are the most abundant ungulates in these forests (Jaksic 1998; Jaksic et al. 2002; Merino et al.2009) and occupy 56% of the area of Nahuel Huapi National Park (Lauría-Sorge & Romero 1999).
In this study we took advantage of the contagious distribution of the mistletoe populations (García et al. 2009) that allows us to compare sites with high and low mistletoe density. We selected six 1-ha native forest sites, separated by more than 2 km. Four sites were located in intact forest lacking introduced ungulates: two sites with high density of mistletoes (>400 reproductive individuals per hectare) and the presence of A. chilensis , and two sites with low density of mistletoes (<20 reproductive individuals per hectare) and the presence of A. chilensis . Two additional sites were located in forests that have been invaded by non-native ungulates. We considered invaded sites those with records of non-native ungulates over the last 100 years. Due to the herbivory pressure by non-native ungulates, the abundance of the mistletoe and its host A. chilensis is low and the hummingbird-mistletoe-marsupial interaction is ecologically extinct (Rodriguez-Cabal et al. 2013). Each site was chosen haphazardly from a pool of possible sites. Fieldwork and data collection were carried out during two consecutive austral springs and summers (2017-2018 and 2018-2019).