Marmots from space: assessing population size and habitat use of a burrowing mammal using publicly available satellite images

Abstract

Social, burrowing mammals such as prairie dogs, ground squirrels or marmots are keystone species in grassland ecosystems. Grasslands have been converted into cropland or pastures globally, yet it remains virtually unknown how this has affected the biogeography of burrowing mammals, as efficient, broad-scale survey methods are lacking. We aimed to test whether structures created by burrowing rodents can be reliably detected on publicly available, very-high-resolution satellite images, in order to assess rodent distribution and abundance. We identified burrows of Bobak marmot (Marmota bobak), a keystone burrowing steppe rodent, on 1300 randomly selected plots of 1 km diameter (78.53 ha) across the species’ range (~950 000 km²) in Kazakhstan and southern Russia using Google Earth and Bing images. We then used burrow occurrences and species distribution models to map marmot distribution. We assessed how marmot occurrence and density vary across land-use types. We also combined satellite-based burrow densities and ground-survey data to derive a new population estimate for the species across Kazakhstan. We mapped a total of 7425 burrows from the satellite imagery. Field visits at a subsample of burrows suggested that burrow occurrence was detected reliably. Broad-scale marmot distribution was mainly determined by summer rainfall, land use and elevation. Occurrence probability was highest on arable croplands, followed by abandoned croplands and grazed steppe. The current Bobak marmot population size for Kazakhstan was estimated at 6.1 (±2.4) million individuals. Our results demonstrate that publicly available, very-high-resolution images can be used to reliably map the distribution of burrowing mammals across large geographic scales. The observed and predicted distributions indicate that the Bobak’s range has remained almost unchanged in Kazakhstan since the 1950s, despite several drastic episode of land-use change. This suggests that burrowing mammals can be remarkably resilient to land-use pressure, questioning prevailing narratives of population collapse in these species following agricultural expansion.