Roads as ecological traps for giant anteaters

Abstract

Wildlife-vehicle collisions (WVC) represent a serious source of mortality for many species, threatening local populations' persistence while also carrying a high economic and human safety cost. Animals may adapt their behaviour to road associated threats, but roadside resources can act as attractants, providing misleading signals about the quality of roadside habitats, ultimately acting as an ecological trap. Yet, the extent to which individuals modify their behaviour and space use to roads is largely unknown for most taxa. Using fine-scale movement data from 41 giant anteaters (Myrmecophaga tridactyla), tracked in the Brazilian Cerrado, we aimed to identify facets of movement behaviour that might exhibit plasticity to roads and traffic volume. Specifically, the analysis of daily and instantaneous movement speeds, home range characteristics, and crossing rates/times, allowed us to test for an effect of road proximity, traffic volume and natural linear features on movement behaviour. We found no effect of road proximity or traffic volume on space use or movement behaviour. While individuals tended to reduce their movement speed when approaching roads and crossed roads ~3 times less than would have been expected by random chance, none of the highways we monitored were impervious. The majority of tracked anteaters living near roads (<2km) crossed them, with higher crossing rates for males. Consequently, habitat near roads may function as an ecological trap where healthy individuals occupy the territories nearby or bisected by roads but eventually are road-killed given their regular crossings, leaving the territory vacant for subsequent occupation. Crucially, we found no evidence that anteaters actively searched for passage structures to cross the roads. This suggests that crossing structures alone are unlikely to mitigate WVC induced mortality. Our research reinforces the need to implement fencing, properly linked to existing passages, and minimising the amount of night-time driving to reduce the number of WVCs.

Assessing the impact of roadkill on the persistence of wildlife populations: a case study on the giant anteater

“…For our calculations, we did not consider the dispersal periods but included the data of the two anteaters that settled in new territories (1 month after stopping the dispersal). Previous research showed that there are no significant differences in habitat between roadsides or across roads (Noonan et al, 2021). Estimates of survival were performed using the Kaplan-Meier estimator (Rich et al, 2010) through the R package ‘survival’ (Therneau, 2021).…”

“…3350 in the west section (Fig. 1B) and 3850 in the east section (Fig.1C) (DNIT, 2020) (see for further details on study area in Ascensão et al 2021 and Noonan et al 2021).…”

“…Movement data of giant anteaters has been collected for the past five years (2017-2021) in the vicinity of three of the paved roads (Fig. 1C-E) (Noonan et al, 2021); currently totaling 46 adult wild giant anteaters (25 females and 21 males). In this dataset, four anteaters (ca.…”

“…The anteaters were tracked on average 395±235 days (range: 46-1089, fixes obtained every 20 min.). All details about capture and movement data are provided in Noonan et al (2021).…”

“…We considered two groups of resident anteaters, distinguishing those anteaters whose centroid of the home range was far (> 2 km) from paved roads (G 1 , n=20) and near (< 2 km) paved roads (G 2 , n=24). This distance threshold was selected based on Noonan et al (2021), in which we found that resident giant anteaters with home range centroid distanced > 2 km from a main road had a significantly lower probability of crossing the road, and consequently to be road-killed. For our calculations, we did not consider the dispersal periods but included the data of the two anteaters that settled in new territories (1 month after stopping the dispersal).…”