Individual study: Cold weather reduces trapping success of feral coypus Myocastor coypus in eastern England
Gosling L.M. (1981) The effect of cold weather on success in trapping feral coypus (Myocastor coypus). Journal of Applied Ecology, 18, 467-470
Coypus Myocastor coypus have been feral in eastern England since the 1930s. Due to damage to agriculture (consuming crops) and wild plant communities, coypus were systematically controlled by cage trapping until complete eradication was achieved in the late 1980s. It became apparent that the nocturnal activity period of coypus was reduced during cold weather, a consequence of this being a tendency for coypus to become active during daylight hours. It might therefore be predicted that the number of coypus trapped would be less on cold than warmer nights, based on the assumption that an individual would cover less ground during a shorter activity period and thus have a lower probability of encountering a trap. If this were so, this might influence the degree of trapping effort considered worth while during cold weather. The analyses reported here were designed to test the prediction of lower trapping success during nights with low night-time temperatures.
Data were obtained from the records kept by the trappers of the 'Coypu Control' organization. On each working day trappers noted the number of traps set and the number of coypus caught. An average of 29 (± 15) traps were set per night on four nights of trapping each week. The analysis was restricted to the winter months (November to March) and covered the six winters of 1973-74 to 1978-79. Daily minimum temperatures were used in the analysis, which used effort-standardized measures of trapping success, i.e. number of coypus killed per unit of trapping effort.
Two measures were calculated for each of the 484 nights of trapping: the numbers of coypus caught per 100 traps set; and the numbers of coypus caught per trapper.
Inferences on activity were made from observations of coypu footprints, or their absence, in overnight snow at a long-term study site in northeast Norfolk (including Calthorpe Broad) supporting between 20 to 60 coypu.
Both measures of trapping success declined in a linear fashion with minimum temperature. On cold nights a lower percentage of traps caught coypus (c.8% at -7º C minimum temp.; c. 13% at 11º C minimum temp.) and fewer coypus were caught per trapper. Considering the difference between +5 and -5º C, there was an 8.5% reduction in the number of traps set but a 33.6% reduction in coypus caught per trapper. This decline may be partly due to the absence of nocturnal activity in cold weather by some coypus, e.g. in the Calthorpe enclosure an absence of footprints was observed in snow that had fallen the previous day. Similar observations were made by trappers in areas where many coypus were subsequently trapped. On other cold days one or a very few trails were found. In these cases either all or the majority of individuals had remained in burrows, or on above-ground nests, during the night.
Conclusions: Coypu trapping in East Anglia was conspicuously less successful during cold than warm winter nights.
Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28198108%2918%3A2%3C467%3ATEOCWO%3E2.0.CO%3B2-K