The records of animals caught by two kinds of breakback trap (Reporter and Museum Special) have been analysed to investigate the ways in which the catch of a trap may be selective. The data comprise 1583 individuals belonging to 12 species of small mammal.
The Reporter trap tends, in two distinct ways, to catch individuals which are heavier. Firstly, the proportion of the total catch of a given species caught by Reporter increases with the mean weight of the species. Secondly, within each species (with one trivial exception) the individuals caught by Reporter are, on average, heavier, the mean difference being 36%. In both of these respects significant species x trap interactions remain after the effect of species mean weight have been corrected for.