Surveying wolves without snow: a critical review of the methods used in Spain

Abstract

Wolves (Canis lupus) are dicult to survey, and in most countries, snow is used for identifying the species, counting individuals, recording movements and determining social position. However, in the Iberian peninsula and other southern regions of its gobal range, snow is very scarce in winter, so wolves must be surveyed without snow. In Spain and Portugal, wolves are surveyed through estimating number of wolf packs in summer by means of locating litters of pups when they are at rendezvous sites. Packs are confirmed when pups are observed or respond to simulated howling. We make a critical review of this method, exploring the sources of error when estimating number of packs, the constraints of the simulated howling method, the sources of uncertainty caused by variations in eort, in observer experience and in other variables. We stress the diculty of assessing average pack size and percentage of wolves not included in packs (pairs and solitary wolves), which can exceed 30% of the population. These restrictions make this method unaccurate and unable to detect moderate or even large population size variations. At the same time, indices based on abundance of wolf tracks and scats is hampered by the lack of snow and the problem to distinguish them from those of dogs. We conclude that accepting the limitations of these wolf surveys and highlighting the uncertainty of the figures they provide is more realistic and will encourage a more prudent approach to wolf management.