Evaluating the effect of the mesopredator release hypothesis on the nest survival of grassland birds in NE Argentina.

DI BITETTI, MARIO S.; GOT, NOELIA; DI GIACOMO, ALEJANDRO G.; PASIAN, CONSTANZA; ADRIAN S. DI GIACOMO; TURBEK, SHEELA; BROWNE, MELANIE

Puerto Iguazú

Congreso; Ornithological Congress of the Americas; 2017

Aves Argentinas

The ?mesopredator release hypothesis? suggests that, in the absence of top predators, mesopredator populations will increase disproportionately, causing local prey populations to decrease or disappear. In Corrientes, there are no stable populations of cougar (Puma concolor), and the jaguar (Panthera onca) has been extinct for more than 60 years. In contrast, eastern Formosa maintains abundant cougar populations. In 2015, we used camera traps to study the community occupancy of nest predators in both sites, and found a pattern corresponding with the mesopredator release hypothesis (Fox occupation: 0.99 in Corrientes and 0.26 in Formosa). The aim of this study is to evaluate if there are differences in the nest survival of the Strange-tailed Tyrant (Alectrurus risora) and Tawny-bellied-Seedeater (Sporophila hypoxantha) between these two areas. The study was conducted in the Reserva El Bagual (REB), Formosa, and the Reserva San Nicolás in the Iberá Wetlands (RNI), Corrientes. During 2016, we monitored 96 nests. The daily survival rate (DSR) of A. risora was greater in REB for the nestling period (DSR= 0.951 and 0.881 respectively, !2= 4.32, P= 0.0376); however, no differences were observed during the incubation period. In the case of S. hypoxantha, no differences were found in either of the periods (mean DSR= 0.94). The difference in the DSR of A. risora could be explained by the greater abundance of mesopredators in RNI. However, the DSR of S. hypoxantha could be attributed to differences in nest visibility due to different nest substrates: RNI (hidden between grasses) and REB (visible in herbaceous plants and bushes).