Relationships between grassland shorebirds abundance and landscape characteristics in South American wintering areas

MARTINEZ CURCI NS; ISACCH J

Workshop; Buff-breasted Sandpiper Conservation Workshop.; 2017

Most of our knowledge about requirements of grassland shorebirds in wintering areas comes from studies that evaluated the response of shorebird abundance to patch-level characteristics of habitat. However, the relative influence of landscape variables is poorly understood. We know that American Golden-Plovers (Pluvialis dominica) and Buff-breasted Sandpipers (Calidris subruficollis) depend on short grassland. However, many of the areas with seemingly adequate habitat are not used. Although it is possible to identify different types of vegetation, the main constraint for landscape-scale studies had been the difficulty to differentiate tall and short pastures using satellite imagery. We will evaluate the influence of landscape variables in the patterns of abundance and distribution of grassland shorebirds and use this information to construct habitat suitability maps. To overcome the difficulty of not being able to differentiate between short and tall grasslands using remote sensing, we are going to use the normalized difference vegetation index (NDVI) from the MODIS project to estimate forage above-ground net primary production (ANPP). It is known that different pasture types show different patterns of annual variation in the ANPP. The ANPP is determined by vegetation structure and its capability of fixing carbon, and has a considerable annual variability. Different pasture types show different patterns of annual variation; and within the same pasture type, the ANPP usually decreases with grazing because it modifies vegetation structure and leaf area. It is also known that grazing strategy affects shorebirds abundance. Abundance is greater in paddocks with continuous grazing (in which cattle is maintained through the year) than in those with rotational grazing (in which cattle is rotated several times among different paddocks throughout the year), while there are no shorebirds under winter grazing (in which grazing occurred only during austral autumn and winter). Our first specific goal is to integrate this knowledge to evaluate the relationship between shorebirds abundance and the annual variations of ANPP associated to different grazing strategies. Our second specific goal is to model shorebirds abundance and distribution as a function of landscape-scale variables, including the metrics of the ANPP obtained from the specific objective 1. Finally, our third specific goal is to construct habitat suitability maps that allow extrapolating density estimates over the study area. If we find significant associations between landscape variables and shorebirds abundance, this methodology could be replicated in Brazil and Uruguay to obtain habitat suitability maps that allows for more precise population estimates. Also, time series analysis can be developed to evaluate the relationship between inter-annual variations in the ANPP and shorebirds abundance. The stability of grazing strategy and therefore of the ANPP in a given ranch might explain shorebirds site fidelity.