The Zoologist/4th series, vol 6 (1902)/Issue 728/Statistics relating to British birds, Horwood
STATISTICS RELATING TO BRITISH BIRDS.
By the Rev. A.R. Horwood.
When we are told that the number of birds on the British list amounts to 415 species, most of us are at first inclined to treat this statement cum grano salis, as though it were a fabrication. On further consideration, however, we shall see that after all this is quite possible—that is to say, if we assume that the 415 birds are not all with us at the same time.
Allowing, then, that there are two well-defined seasons in the year—summer and winter—and also that there are two primary classes of birds on the list—resident and migratory—we see our difficulties somewhat disappear. Observing further that the latter of these two classes may be subdivided into two further classes—summer and winter migrants—we then see that it is comparatively easy to account for the apparently large number of so-called British Birds. This last phrase is used advisedly, for it must be patent to all that some of our British Birds have very little title to the name.
And thus we find there is a fourth class, beside the resident, the summer, and winter migrants, namely, the accidental or occasional straggler to our islands. Owing to many causes—such as migration, gales, and probably, to a greater extent than is generally imagined, to the escape of rare captive birds—our list of accidental visitors is a long one.
To this last class might be added a fifth—the extinct class; but as only one species that has lived within the memory of man in England has so disappeared, we may, I think, omit this class; for it only includes the now world-famous Great Auk, which became extinct about two hundred years ago.
Having reduced our list of birds to four—or, if preferred, five—great classes as regards occurrence, and using the same terms for their degree of frequency, we may, without going into too close details, examine the matter more carefully with respect to families and genera.
In our examination we will, for sake of uniformity, invariably follow the order of classification and nomenclature of Seebohm.
We give below a classified table to illustrate our meaning more clearly: —Taking the families in the table first, we see that there are twenty-nine families, with an aggregate of 415 species. For a small area like the British Islands, this is a very large percentage, at first sight, of the total known species in the world, which number about 12,500.
Looking now at the total number of species in each family, we see that the Passeridæ hold the first rank, numbering 140, or one-third of the whole number. As our finest songsters are found in this family, we must look on this with great satisfaction.
The next in order of number are the Charadriidæ (56), then come the Anatidæ (44), followed by the Gulls and Terns, or Laridæ (32), lastly, the Vultures and Eagles (31).
That the largest number of species includes the smallest birds, and that the largest birds are in the minority, is only natural, considering the small area and populous state of the country. Here it may be added that the largest British bird is the Mute Swan, measuring 5 ft.; and the smallest bird is the Golden-crested Wren, measuring 3½ in. from tail to beak.
Of resident species, we can now boast 137 species. Several species—such as the Kite, Bittern, Bustard, Crane, and others—used to be resident, whereas they are now only accidental visitors. Of these only five families run into double figures, the Passeridæ being again predominant; whilst next in order are the Anatidæ; then come the Charadriidæ, the Laridæ, and then the Falconidæ.
The total number of resident birds, it will thus be seen, is about one-third of the total number on the list.
Taking next in consideration the summer migrants, which come to us in April and leave us at the latest in October, we find the number that visit us is sixty-eight. Of these fifty are Passeridæ, and none of the rest run into double figures; whilst many of these latter only visit us occasionally, and many of the Passeridæ are resident in certain localities.
This makes our total breeding birds to number 205. Really only about 187 can be said to breed with us regularly, and some of these only locally. This number, it will be noticed, hardly amounts to half the total number.
Owing to the fact that many of our winter migrants only frequent out-of-the-way spots, we can only record thirty-nine regular species. These belong mostly to the Anatidæ and Charadriidæ.
Next in order is the fourth class—the accidental and occasional visitors. These amount to 169, but owing to the difficulties of observation many of them may undoubtedly be classed as regular spring, autumn, or winter migrants.
In the same way the numbers of the other classes must be modified according to locality, period, and observation.
Of the fifth class, only one species—the Great Auk—is exemplary. One species—the Little Owl—may also be classed as a lately introduced bird, like the Red-legged Partridge of an earlier date.
Thus, then, we see how it is possible for the birds on the British list to amount to 415 species, since considerably over one-third are accidental visitors, and barely half of them remain to breed with us. After all, when we consider the fact in all its bearings, it is not so very surprising if we look at it from a world-wide point of view. Our islands are situated in the temperate regions, where birds that live in the warmer regions migrate to breed. We get, then, birds from the semi-tropical regions, and birds on their way to and from the far north from our own region. In a similar way we are situated only a few miles, in the south, from the Continent. This in itself explains why our own avifauna is largely supplemented in the summer by visitors from all parts. Indeed, when we come to think of it, we must wonder why many species abundant on the Continent are not met with at all in our own country. We find birds, such as the Stork, breeding in Holland, which from its nature might just as well breed in England.
Lastly, it is not surprising that we receive visits from American species, when we consider the long distances travelled by our summer migrants, and the fact that it is only a five days' trip in the liners of the Atlantic to the New World. How comparatively short a distance must it seem, then, to such an untiring creature on the wing as the bird!
- 'Coloured Figures of the Eggs of British Birds.'