Studies on the Two New Zealand Bats
Fig. 1 records the activity of bats in terms of the number of observations for each month of the year. The basic pattern, reflected in the value for unidentified bats, is of low numbers during the winter months (May to August) followed by a steady increase in numbers from September to mid-summer and autumn. Though values are low, it is noticeable that records of Mystacina are lacking for only two months, March and September, whereas Chalinolobus is not recorded during five months, three of these being the winter months, May, July and August. Fig. 2 records the yearly activity of a small colony of unidentified bats at Puke-titiri, Hawke's Bay, observed by Miss P. Lewis during the years 1956 to 1959. An almost complete absence is noticeable for the winter, the single observation for the months May to July being of a solitary bat in the early dawn.
Of the numerous observations of unidentified bats, 22 record dusk, 22 evening and 10 summer evenings as the sighting time. A few claim that the bats were seen after dark. Confirmed sightings of Chalinolobus state evening as being the period of activity. Roach and Turbott (1953) record this time as the active period for a captive specimen. At Orakei-Korako (Rotorua-Taupo) on the 19th-20th February, 1948, Phillipps (Dominion Museum file) noted the appearance of the first bat from a cave colony at 7.30 p.m., and of the second a little later. No further bats emerged, and both these bats returned at 1.30 a.m.page 21
There are few references to Mystacina in flight. Two records of the entry of this species into lighted huts, and Stead's (1937) reference to the activity of this species in the Stewart Island region after 10 p.m., are relevant. During late February, 1959, a captive Mystacina in the Rotorua-Taupo district consistently roosted till 8 or 8.30 p.m. in the early stages of its capture.
Fig. 3 shows the relationship between the times of appearance of the Puketitiri bats and the times of sunset for 1958. Although affected to some extent by weather conditions, the animals generally appeared between five and twenty-five minutes after sunset. This time is comparable with the data reported for Chalinolobus. Phillipps' record for the 19th February coincides with the Puke-titiri times for the corresponding period of the year. A winter sighting of an unidentified bat in the Rotorua-Taupo district during June, 1958, was at about 14 minutes before sunset.
The duration of the foraging period is difficult to assess. Observations of bats usually last between a few seconds and fifteen or twenty minutes. Longer observations are seldom possible because of the rapidly failing evening light. Captive animals are usually active for only short periods each day. McKay (Internal Affairs file) records that for a captive Mystacina feeding, drinking, and exercise usually occupied three hours. Stead (1937) claimed a two-hour flight period for this species. Roach and Turbott (1953) record 10 minute evening flights for a Chalinolobus specimen. Phillipps' Chalinolobus remained away from the roost for six hours. At Puketitiri sightings have been made at 4.45 a.m. in January, 5 a.m. in March, and early dawn in June.