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Edge effect is an inherent problem when using live-trapping grids to census animals in populations. The relationship between grid size and home range size, shape, and dispersion pattern was investigated by a mathematical model and computer simulation. A simple relationship between overestimate of population density and grid size to home range size was found. To minimize the effect of home range size, shape, and dispersion pattern on census results, grid sizes at least 16 times larger than the average home range size should be used.

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A peak density population of Clethrionomys glareolus was studied by snap‐trapping to determine by experimentation whether spacing behaviour regulated the breeding density. On control plots onset of reproduction was asynchronous, litter size of overwintered females decreased significantly during the summer and no year‐born animals matured during the reproductive period. A removal experiment in the early summer resulted in sexual maturation of year‐born females. A second removal in late summer indicated an inhibition of maturation in year‐born females despite continued intense reproduction of overwintered females. We conclude that spacing behaviour regulated maturation of females early in the summer but other factors, such as food quality, limited maturation in late summer.