No abstract

The Vulnerable marsh deer Blastocerus dichotomus, the largest native cervid in South America, is declining throughout its range as a result of the conversion of wetlands and overhunting. Estimated densities in open wetlands of several types are 0.1–6.8 individuals per km2. We undertook the first unmanned aerial vehicle (UAV) survey of the marsh deer to estimate the density of this species in a 113.6 km2 area under forestry management in the lower delta of the Paraná River, Argentina. During 6–8 August 2019, at a time of year when canopy cover is minimal, we surveyed marsh deer using Phantom 4 Pro UAVs along 94 transects totalling 127.8 km and 8.6 km2 (8.1% of the study area). The 5,506 photographs obtained were manually checked by us and by a group of 39 trained volunteers, following a standardized protocol. We detected a total of 58 marsh deer, giving an estimated density of 6.90 individuals per km2 (95% CI 5.26–8.54), which extrapolates to 559–908 individuals in our 113.6 km2 study area. As it has generally been assumed that marsh deer prefer open habitats, this relatively high estimate of density within a forestry plantation matrix is unexpected. We discuss the advantages of using UAVs to survey marsh deer and other related ungulates.

No abstract

Natural environments have been altered by many human actions and during the last decades this process has been hastened in an alarming way. In the Pampean and Espinal ecoregions of Argentina, agriculture was the major contributor, producing a homogeneous landscape of cultivated lands interrupted by few small, isolated pieces of natural environment or noncultivated lands. We studied bird assemblages in two types of agricultural landscapes, one with crops located within a heterogeneous landscape matrix, such that crops were bordered by different types of noncultivated environments, and the other with crops located within a homogeneous landscape matrix away from noncultivated areas. The main objective was to compare the bird assemblage structure and composition between these two landscapes to test the hypothesis that heterogeneous agricultural landscapes support greater bird diversity than do homogeneous landscapes. We recorded 33% of the total abundance in the crops within a homogeneous matrix (CHOM) and 67% of the total abundance in the crops within a heterogeneous matrix (CHEM). The CHEM points had greater species richness, and composition of species differed between CHOM and CHEM. Thus, the results support the hypothesis that environmental heterogeneity increases bird diversity in agricultural areas, with important consequences for ecosystem services that biodiversity provides to agricultural ecosystems and for the conservation value of these systems. The fact that the protected areas by themselves are not sufficient to guarantee biodiversity conservation emphasises the important role that areas under cultivation can play. Our data provides evidence that the presence of uncultivated environments can increase the importance of agricultural lands for biodiversity conservation and, at the same time, can benefit agroecosystems by supporting bird species that can function as biological control agents of agricultural pests.