46
THE ESSEX NATURALIST
the ricks inside sheaves of corn, but Rowe and Taylor obtained
evidence that at least some positive movement of Harvest Mice
into ricks also occurred. Breeding in ricks was a very rare occur-
rence (unlike House Mice) and with the onset of the breeding
season emigration to the fields was found to occur. Very few
farmers in southern England still build ricks so this habitat is no
longer available to Harvest Mice.
The available records seem to indicate that the Harvest
Mouse was fairly plentiful in Essex throughout the first half of
this century. However, in the last few years it has been suggested
that this species has become rarer due to its disappearance from
what was considered to be its typical habitat: the cornfield. The
early records were from agricultural land because this was the
habitat in which the species was most easily observed, and the
unsuitability of this habitat associated with modern agricultural
practices has resulted in a false impression of rarity. This im-
pression has been accentuated by the difficulty of finding Harvest
Mice even when they are present and the reasons for this are
discussed below.
Harvest Mice are difficult to catch in Longworth traps. This
is probably due to the light weight of this species (maximum of
eight grams) which means that they can often enter and leave
even a sensitive trap without firing it. Also Harvest Mice are very
prone to live above ground level. They can only be caught easily
in late autumn and winter—during the breeding season (late
April to early September) the adults either rarely descend to the
ground or are trap-shy. In the summer trapping survey at Rum-
sey's Nursery only two specimens were caught in 2,352 trap-nights
although several breeding nests were found. Both the captured
mice were juveniles which had probably only recently left the
nest and were in the act of dispersing.
The 'above ground' life of Harvest Mice probably explains
their rarity in bottles, although in investigations outside Essex
bottles placed upright against tall vegetation have often caught
Harvest Mice even when conventional trapping methods have
failed. The catch rate was greater still if the bottle was below
a nest. Behaviour studies conducted by Margaret Wise at Royal
Holloway College have shown that Harvest Mice only enter
bottles with about one tenth the frequency of Wood Mice and
Voles. When this species did enter bottles it showed a marked
preference for bottles placed in the open (in contrast to other
species) and the Harvest Mice were very adept at climbing out of
bottles. From these observations and the trapping results, it
seems that the Harvest Mouse is adverse to entering any object
placed at ground level and hence the difficulty in obtaining
specimens of this species.
There are also a few records from owl pellets. No conclusions
can be drawn from these observations as Hanney (1962) has
shown that the number of minor species taken by the Barn Owl