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Volume 84, 1956-57
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Population Counts of L. archeyi on Mt. Moehau

In January, 1956, the authors endeavoured to obtain some idea of the density and pattern of distribution of the population of L. archeyi inhabiting the open, eastern slopes below the summit of Mt. Moehau (Plate 57, Figs. 1 and 2).

A light rope, 20 yards long, which could be staked in position at each end, was used to mark out the quadrats, the directions of which were obtained by compass. The area one yard on each side of the rope was carefully combed for frogs, the same four searchers taking part in each count All movable logs and stumps were lifted, and all vegetation carefully examined. Findings for each side of the rope were recorded separately in terms of body lengths, numbers and groupings of frogs, and colour patterns.

The results of these tentative investigations, excluding body lengths, are shown in Table I. From a mathematical point of view they are extremely inadequate, and it is hoped that further field work will remedy their deficiencies. Unfortunately the time taken to examine an area of even 20 square yards with maximum care and to record necessary observations is considerable. In addition, access to the summit of Mt. Moehau is relatively tedious and weather fluctuations inhibit continuous fieldwork.

From the few figures available in Table I, however, it is possible to make some general observations:

(i) The frogs are clearly grouped in colonies.

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Table I.—Distribution of Leiopelma archeyi On MT. Moehau.
Count No. Direction No. of Individuals Colour Patterns* Area Covered
1 N.S. 0 20 sq. yds.
2 N.S. 0 20 sq. yds.
3 E.W. 4 + 1 = 5 ab, b, ba, 2ca. 20 sq. yds.
4 E.W. 5 a, ab, 2b, c. 20 sq. yds.
5 N.S. 1 b. 20 sq. yds.
6 N.S. 2 ab, ac 20 sq. yds.
7 E.W. 1 + 5 = 6 ab, b, 2c, 2ca. 20 sq. yds.
8 E.W. 4 a, b, 2c. 20 sq. yds.
9 N.S. 2 ba, c. 20 sq. yds.
10 N.S. 0 20 sq. yds.
11 E.W. 4 a, ab, b, c. 20 sq. yds.
12 E.W. 0 20 sq. yds
13 N.S. 0 20 sq. yds
14 N.S. 3 a, ab, b. 20 sq. yds
15 E.W. 4 ab, b, 2c. 20 sq. yds.
16 E.W. 2 + 2 = 4 2ab, b, ba 20 sq. yds.
Total: Total: Total Area:
= 40 frogs 4a = 320 sq. yds.
= 14 colonies 10b
9c
9ab
3ba
1ac
4ca

(ii) The obvious means are 2.50 frogs per quadrat (or unit area of 20 square yards, 2.86 frogs per colony, and 0.875 colonies per quadrat.

The distribution of the frogs was examined from the standpoint of a colonial grouping. A Poisson distribution, as might perhaps be expected, did not fit these data at all well. A Neyman Type A contagious distribution (Skellam, 1955, 96) was tried (roughly allowing for the fact that having found one frog the probability of finding another frog in the quadrat was rather higher), but although the goodness of fit appeared to be satisfactory the actual figures obtained do not at the moment appear to be of much relevance. It is possible that they can be correlated with egg clusters laid in a certain area from which frogs reach a particular quadrat, but more data are necessary before really useful results can be obtained. No counts of this kind have so far been carried out during the breeding season.

It should be emphasised that almost nothing is known of the movements of L. archeyi from place to place. Marking experiments would undoubtedly be valuable in this connection.

[Footnote] * For key to colour pattern see above.

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