Capture rates of birds in the high Andes of Ecuador

There is a long history of using birds as indicators of pervasive environmental threats. In the High Andes, birds face potential threats from global climate change and from the impacts of land use changes associated with logging, grazing, fire, and agricultural expansion. We use an 11-year constant effort, avian mist netting data set from two protected areas in the High Andes of Azuay province, Ecuador, to explore how environmental change is affecting resident bird species in high-elevation habitats. We estimated a statistically significant mean decrease of 2.8% in capture rate across years for the full species assemblage and across all habitats. Species-specific capture rates across habitats declined for 29 of the 38 species that met our inclusion criteria. When species were grouped by diet, body size, primary habitat occupied, or habitat breadth, capture rates did not change differently among ecological groups of birds. Although we cannot identify the mechanisms behind the decline, the broad nature of the decline suggests that human-induced environmental changes, including warming, altered rainfall patterns, and intensification of land use, could be acting in combination, resulting in a decline in the populations of many bird species in the region’s protected areas. This study highlights how events occurring outside of protected areas may affect resident bird species in these high-elevation habitats.

Methods
Our study was conducted in the Llaviuco Valley (02.840° S, 79.160° W) of Cajas National Park, and the adjacent 2700 ha Mazán Reserve (02.870° S, 79.120° W) in the High Andes of Azuay province, Ecuador. Sample sites were placed in three unique habitats. These included: (1) native forest (MASE) in the Mazán Reserve; (2) non-native forest (MAIN) also in the Mazán Reserve; and (3) shrubland (LLAV) in the Llaviuco Valley. In 2006, we established a “long-term” bird-monitoring program using standardized methods of constant effort mist netting. Each of our three sites was sampled three times annually (2006–2016) to cover the rainfall seasonality of the study area; we sampled during the main rainy season (21 March–6 May), the dry season (19 July–9 September), and the secondary rainy season (30 October–20 December). At each of the three sites, we captured birds by dispersing 20 mist-nets (12 x 3 m, 30 mm mesh) throughout a selected habitat, with individual nets placed along or perpendicular to narrow paths, or in small gaps in understory vegetation.