Saturday, 26 December 2015

Spatio–temporal hotspots of satellite–tracked arctic foxes reveal a large detection range in a mammalian predator



The scale at which animals perceive their environment is a strong fitness determinant, yet few empirical estimates of animal detection ranges exist, especially in mammalian predators. Using daily Argos satellite tracking of 26 adult arctic foxes (Vulpes lagopus) during a single winter in the High Canadian Arctic, we investigated the detection range of arctic foxes by detecting hotspots of fox activity on the sea ice.


While maintaining territories in the tundra, these solitary foragers occasionally used the sea ice where they sometimes formed spatio–temporal hotspots, likely scavenging on marine mammal carcasses. We detected 35 movements by 13 individuals forming five hotspots. Foxes often traveled more than 10 km, and up to 40 km, to reach hotspots, which lasted one–two weeks and could gather up to 12 individuals. The likelihood of a fox joining a hotspot was neither influenced by its distance from the hotspot nor by the distance of its home range to the coast.


Observed traveling distances may indicate a high detection range in arctic foxes, and our results suggest their ability to detect food sources on the sea ice from their terrestrial home range. While revealing a wide knowledge gap regarding resource detection abilities in mammalian predators, our study provides estimates of detection range useful for interpreting and modeling animal movements. It also allows a better understanding of foraging behavior and navigation capacity in terrestrial predators.

Electronic supplementary material

The online version of this article (doi:10.1186/s40462-015-0065-2) contains supplementary material, which is available to authorized users.
Keywords: Argos satellite tracking, Vulpes lagopus, Sea ice, Spatio–temporal hotspots, Detection range, Scavenging, Dynamic Brownian bridge movement model


The scale at which animals perceive their environment determines their ability to locate resources and avoid predators [1, 2], and is thus a key ingredient of individual fitness. Accordingly, it is central to a broad range of ecological fields, including behavioral ecology, movement ecology, landscape ecology and evolutionary ecology [14]. This information is for example critical when modeling animal movements, especially in information–based approaches, where an animal’s decisions need to be set according to its perceptual range or sensory abilities [35]. However, because it is very difficult to estimate, there are few empirical measures of the distance over which animals can assess their environment [1, 6, 7]. The detection range of a species, defined here as the distance over which individuals can discover a resource [7, 8], involves sensory abilities, movement capacities, as well as social foraging tactics enabling information transfer about resource locations [812]. Empirical measurement of detection ranges usually relies on the visual observation of animals [7, 13, 14] or their electronic tracking coupled with an assessment of resource acquisition [15, 16].
Scavengers should be excellent study models to analyze detection range of animals, for they need to locate carrion, a spatially and temporally aggregated resource pulse that can be readily identified by observers. Yet, whereas many studies have focused on the organization of scavenger guilds [12, 1720], little work has been done on the ability of individuals to scavenge [21]. Carrion can attract and concentrate high numbers of consumers, whether they are of local or distant origin [8]. High carrion detection performance is attributed to birds like ravens (Corvus corax) and bald eagles (Haliaeetus leucocephalus) [8, 17], which have an excellent vision [22], can cover large distances at little costs [23] and also benefit from social information transfer [9, 11]. Mammals are usually considered to be less efficient than birds at locating carrion [8, 23].
Arctic foxes (Vulpes lagopus) are facultative scavengers that can feed on marine carrion found on the sea ice during winter [2426]. They can gather in great numbers around marine mammal carcasses [24], have a good sense of smell [27, 28], are able to cover large distances at a fast pace [29], and therefore provide an opportunity to investigate animal detection abilities. From an ecosystem perspective, arctic foxes moving from the land to scavenge on the sea ice can function as active mobile links and resource linkers [30], enhancing the connectivity and energy transfers between the marine and terrestrial ecosystems [25, 31]. Considering the risks and energetic costs of searching resources outside of the usual home range, their ability to detect food in an unfamiliar environment such as the sea ice may influence their foraging decisions and thus their movement patterns, which may in turn influence the flow of nutrients from the sea to the tundra. Therefore, it is important to investigate the detection range of such mobile species. Here, we show through satellite tracking that arctic foxes foraging on the sea ice can reveal an unexpectedly long–distance detection range in a mammalian scavenger.
We answer two specific objectives. First, using the tendency of foxes to gather near carrion, we locate areas intensively used by foxes on the sea ice and identify the number of individuals at these spatio–temporal hotspots, the distances traveled by foxes to reach them, the individual variation in timing of arrival, and the time spent by foxes at hotspots. Second, by analyzing their pattern of use of the sea ice and their participation in hotspots, we assess the detection range of arctic foxes