2.1 Shrews, study area and trapping
Sorex araneus (Figure 1) were collected between 1953 and 2004 in
Białowieża National Park, preserved in alcohol and stored in the
zoological collection of the Mammal Research Institute, Polish Academy
of Sciences, in Białowieża. Shrews were trapped in a mesic broadleaved
forest with a transition to a moist broadleaved forest, mainly in
compartment No. 371 (52°44’ N, 23°52’ E) but also in adjacent Nos. 369
and 370 (see Dehnel 1949 for a map; all these compartments are in the
strict reserve). This type of forest is classified as a subcontinental
oak-lime-hornbeam forest Tilio-Carpinetum . The mean age of the
trees exceeded 100 years, and the amount of dead wood on the ground
averaged 50 m3 ha-1.
S. araneus were caught with pitfall traps (cylinders 30 cm deep
and cones 45 cm deep). After 1965, wooden live traps were additionally
used. We selected and measured the skulls of shrews from the three main
stages of Dehnel’s phenomenon: summer individuals in their first
calendar year (hereafter “juveniles”) caught from July to August,
winter individuals (“subadults”) caught from December to February, and
mature spring/summer individuals in their second calendar year
(“adults”) caught from April to August. After 1981, juvenile
individuals were trapped only in July. There was no winter trapping at
all after 1985. We also measured three individuals each from June
(juveniles), September (juveniles) and November (subadults) from
1955-1985. The sex of all individuals (determined by dissection) was
noted on their labels.