NOTULAE ENTOMOLOGICAE - Helda

122 NOTUI^AE ENTOMOI.OGICAE Xt,lll, 1963
No traces of voles were observed (June 15 — 18) and probably most of the
burrows studied were abandoned in 1962.
3. Burrows under stones and roots on a shady north slope near the station.
The burrows were probably made by the Norway Lemming {Lemmus lemmus).
Trapping with bait was tried in three burrows. Port Salut cheese was used
as bait.
2. The microclimate in the b ur r o iv s
Moisture. The moss surrounding the rather superficial burrows of Clethrionomys
rufocanus at Patoniva was, at least in mid-June, rather wet and the
air humidity of the burrows must have been about 100 per cent R.H. Whether
this high humidity remained unchanged until August is not certain. In the
other two kinds of burrows studied it can be taken for granted that a high air
humidity (about 100% R.H.) prevailed throughout the summer.
Temperature. Maxima and minima were measured in three burrows, in
one at Patoniva (superficial burrow in the moss layer), in one under a birch
root on a sunny slope at the station and in one of the burrows probably made
by the Norway I^emming (under a stone on a shady slope near the station).
At Patoniva weekly maxima and minima were measured; in the other two
cases the temperature was measured daily. The results are given in figs. 1—2
and in table 1. The temperature conditions in the burrows of type 2 (under
roots of Betula in more or less sun-exposed places) can be expected to vary to
a certain extent, depending on the degree of sun-exposure and the water content
of the soil, but the case shown in fig. 1 is probably fairly representative
of this type. The diurnal amplitude on sunny days is considerable (29.VI.10°C),
on rainy or dull days 2.5—3°. The maximum temperature during the period of
investigation was +12,5°C. The diurnal temperature sank to 4-2° or lower
6 times during the period (18—21.VI., 29.VI., 26.VII.). The temperature conditions
in the burrows in the moss layer at Patoniva (type 1) are represented
by the data in table 1. The weekly maxima and minima indicate conditions
rather similar to type 2 but as these burrows are closer to the surface and only
covered with moss, stronger diurnal fluctuations can be expected and are also
indicated by the amplitude of 13° during the period 1—8.VII. The third type
of burrow investigated, namely those under stones and roots on a northern
slope, is represented by the data given in fig, 2 (measurements from a lenmiing
burrow under a stone and about 30 cm from the entrance, 20 cm below the
soil surface). The diurnal variation of temperature was small throughout the
period of the investigation, at most 2° (22.VI.). The maximum during the
entire period was + 5° (June 22, 23 and 24), the minimum 0.5° (29.VI.).
The above temperature conditions differ greatly from those in Microtus
and Chlcthrionomys burrows during the warm period in the more southern