Morphological differences between Marsh Tit Parus palustris and Willow Tit P. montanus in Hokkaido

Abstract

In Japanese Islands, P. montanus restrictus distributes as resident in Hokkaido, Honshu, Shikoku and Kyushu, which are four large islands in Japanese Islands. On the other hand, P. palustris hensoni inhabits as resident in only Hokkaido and its adjacent small island, Rishiri, and therefore the two species are sympatric in Hokkaido.
In this paper the morphological differences between the two species in the hand are mentioned on the purpose of clarifying identification criterion for Japanese banders.
During autumn banding in Hokkaido, 1975, the differences of (1) the size and shape of beak, (2) the colour of head cap, (3) the colour of outer web of large wing feathers, mainly secondaries, and (4) graduation of tail were compared and measured for 50 birds of P. palustris hensoni and 32 birds of P. montanus restrictus.
Wing length and body weight of the two species are shown in Table 1 and Figure 1. From these, body size of P. palustris hensoni is a little larger than P. montanus restrictus as a whole.
Beak length (exposed culmen), beak height, and beak width of the two species are shown in Table 2, Figure 2, and Photograph 1. From these, apparently beak size and shape of P. palustris hensoni is stout and short, as compared with, beak of P. montanus restrictus is fine and long.
Further indeces of the characteristics of beak shape were considered (Figure 5 and 6). One index, I₁ is the product of beak height and beak width (Fig. 5), and another index, I₂ is the ratio of I₁ and beak length (Fig. 6). They separate clearly the differences of the thickness of beak base of the two species.
The differences of colour of outer web of secondaries and also head cap are good indicators to identify the two species.
The measurements of graduation of tail are shown in Table 4. The birds which graduations of tail are 2-4mm are 96% of P. palustris hensoni out of 48 birds, while in P. montanus restrictus the birds which graduations of tail are 5-8mm are 93% out of 28 birds (Table 4 and Photograph 2).
By checking the four morphological differences above mentioned, all birds of the two species were easily identified.
Incidentally, on Honshu, Shikoku, and Kyushu P. palustris hensoni is absent. It is evident that the habitat of P. montanus restrictus is conifer forests through all seasons. We think from our observations that at the least on northern and eastern parts of Hokkaido, P. montanus restrictus occupies, of course, again conifer forests and also the breeding habitat of P. palustris hensoni is rather conifer forest than broad-leaved forest, and that they are ecologically isolated in the way which they live in the same habitat but separate feeding.