Studies on the effects of bait and sampling intensity on trapping and estimating Wood mice, Apodemus sylvaticus

Abstract

The effects of baiting a Longworth trap with whole oats and the density of traps on an area, or sampling intensity, on trapping and estimating Wood mice were studied on two neighbouring woodland plots in November 1971. Standard capture‐mark‐recapture (CMR) methods were used for two weeks followed by five nights of removal trapping. The presence of bait significantly increased the likelihood of capturing marked and unmarked animals. By increasing the sampling intensity a greater proportion of the population was sampled, although the number of animals captured per trap night decreased. These results have been related to the “effective” number of traps on an area. Observations on population structure, weather, movement and capturing marked and unmarked animals have been made. CMR population estimates closely resembled the cumulative number of individuals captured in each study and were for the main part lower than the estimates from the removal trapping carried out at the end of the studies.

Observations on trap response in confined populations of Wood mice, Apodemus sylvaticus

“…Heterogeneity of trap response in Wood mice has been demonstrated in these studies and this was particularly apparent when the sampling intensity was low. In the main the relative trappabiliites between members of a population did not change with time suggesting its inherent basis (Andrzejewski, Fejgin et al, 1971 ;Crowcroft & Jeffers, 1961 ;Young et al, 1952), although Gurnell (1976) has shown that the probability of capture in Wood mice in field studies improves after the initial capture.…”

“…In the present studies, and in comparison with the work of Crowcroft & Jeffers (1961) on House mice, there was no evidence of territoriality (even in study 3) and it is clear that all members of a population had access to all the traps. The set-up was very different from the field situation for these wild mice and the traps probably had more significance in the laboratory as objects for exploration rather than sources of food (see Gurnell, 1976). The method has been most suitable for studying individual variation in trap response according to the number of traps available.…”

“…They were individually toe-clipped and weighed and the breeding condition noted before the start of a period of study. Three studies were carried out using Longworth traps; the traps contained oats as food, but at no time were they baited (see Gurnell, 1976). In studies 1 and 2 the populations were maintained on a 15-hour day, 9-hour night reversed day-night light cycle; study 3 was under natural lighting conditions.…”

“…The traps were always distributed evenly throughout the pen. Here the number of traps per animal will be used as the sampling intensity, rather than the number of traps per unit area (Gurnell, 1976). The sampling intensity was increased in stages in studies 2 and 3 and decreased in the second part of study 1 .…”

“…Moreover, attempts to specifically investigate trap response in the field (e.g. Gurnell, 1976) are hampered by lack of information on the animals not captured in the population. A method to overcome this problem is to live trap confined populations of animals; this has been done, for example, by Andrzejewski, Petrusewicz et al (1959) on laboratory white mice and Crowcroft & Jeffers (1961) on House mice.…”