An indirect method for assessing the abundance of introduced pest Myocastor coypus (Rodentia) in agricultural landscapes

Abstract

Pest management requires the development of robust monitoring tools. In Italy, coypu Myocastor coypus (nutria) have been controlled since the early 1990s, but the effectiveness of these measures has never been tested. With the aim of developing a reliable and volunteer‐based method for the long‐term monitoring of coypu abundance in agricultural landscapes, we calibrated an index based on surveys for coypu paths against density estimates obtained through a standardized mark–recapture technique. Two trapping sessions were performed in winter for each of 12 1‐km long stretches of irrigation canals and watercourses using 15 baited cage traps. Trapping sessions lasted 7 days each, with a 10‐day break between sessions. Population size was assessed using three methods: Peterson–Lincoln's formula, capwire estimators and accumulation curves. Active coypu paths and five habitat variables were recorded by walking on the edge of both banks. The variables were then related to population size (y) by means of multi‐regressive models, testing for the predictive power of the selected models by leave‐one‐out cross‐validation. Multi‐regressive models included only the number of coypu paths with the best performances achieved by the model based on Peterson–Lincoln formula, supporting path count as an effective method to assess the abundance of the coypu in agricultural landscapes. Concurrently, to assess the field suitability of the indirect method, surveys for coypu paths were carried out on 122 randomly chosen 3‐km long stretches of irrigation canals and watercourses in the central part of the River Po valley (c. 15 000 km2; N Italy). The highest (>8/100 m) mean number of paths was recorded in the central part of the study area. According to the regression models, the overall number of coypu is predicted to range between 350 000 and 1 100 000, raising doubts about the effectiveness of current control measures.

Spatial bias in dietary studies can limit our understanding of the feeding ecology of large carnivores

“…So far, few studies explored the extent to which wolves could rely on this species (Ferretti et al, 2019) and none was carried out in areas, like Cluster 4 and 5, where domestic or wild ungulates are scarce. As coypu are easy to catch in agricultural channels and could attain significant densities (Balestrieri et al, 2016), it is plausible that they are indeed a major prey for wolves. Empirical evidence seems to confirm this point: by analyzing the stomach content of 64 wolves that were found dead in the Po Plain (Cremona, Mantua, and Bologna provinces), we found remains of coypu in 10 individuals (15.6%) (see Appendix 2).…”

“…Finally, we also included the potential environmental suitability of the Italian peninsula for the coypu. Recent studies found out that the coypu can be an important prey, in some agricultural ecosystems of Central and Northern Italy (Musto et al, 2024;Ferretti et al, 2019), probably because it is easy to prey and can attain very high densities, providing wolves with a relevant biomass (Balestrieri et al, 2016). As no abundance map was available for this species, we rather use the potential suitability of the Italian landscape, at a 1 km resolution, obtained from Schertler et al (2020).…”

Evaluating the effectiveness of footprint platforms to detect invasive mammals: coypu (Myocastor coypus) as a case study

“…The methods commonly used to detect the presence of coypu include the direct observations of animals (Marini et al, 2011) or the detection of active burrows (D'Adamo et al, 2000), feeding signs (Corriale et al, 2006) or paths used by the animals (Balestrieri et al, 2016). All these methods require a search in the field that could be time expensive.…”

“…All these methods require a search in the field that could be time expensive. Furthermore, they have not been tested against presence and absence of the species, but see Balestrieri et al (2016) for a quantitative approach. A technique not yet tested with coypu, but widely used to detect many other mammal species (Zielinski and Truex, 1995;Gillies et al, 2003;Connors et al, 2005;DeSa et al, 2012), is the use of tracking plates: plates covered by a plastic medium used to detect the footprints of animals.…”

Prospects for crowdsourced information on the geomorphic ‘engineering’ by the invasive Coypu (Myocastor coypus)

“…The most critical damage caused by Coypu, in purely economic terms, is that to drainage structures, with direct costs for the structure management, and indirect costs connected to flooding (Baker, 2006;Cocchi and Riga, 2008;Viero et al, 2013). In recent years, Coypu-related problems have been increasing rapidly in several countries, including Italy (Cocchi and Riga, 2008;Balestrieri et al, 2016), with millions of € of estimated damage and control activities (Panzacchi et al, 2007). In Italy, the Coypu was imported in the 1930s.…”