Wren - a markedly hardy bird
Below is an extract from an article by Prof C. J. Patten that appeared in the edition of The Irish Naturalist journal of July 1912. It was headed: Wrens on Migration Observed at The Tuskar Rock and Lighthouse. The Tuskar Rock is off the coast of County Wexford.
When I went up to the lantern to study migration, it was my custom to remain all night out on the balcony.
Thus when wrens came along, I managed to secure four, one on the night of the 13th of April, and three during the next night.
None of these birds struck in the strict sense of the word.
They came to the lantern glass as softly as would a moth. Indeed, a cockchafer attracts far more attention than a wren when it comes in contact with the glass.
The wren comes along very quietly, makes little, almost no noise at the glass, and straight away settles down to rest in a recess or on a sash of the window pane.
Now the evidence afforded by the presence of a limited number of wrens at the lantern of a tall tower, such as the Tuskar, which rises up from a rock almost on the sea level, is little or no criterion of the numbers actually on migration.
Far greater numbers of this species frequented the rock in the intervening daytime than ever were seen round the lantern at night, thereby affording evidence that the flight of the wren during migration is relatively low and so the lantern is avoided.
This is very much strengthened by the fact that those wrens which appeared at the lantern came flying almost perpendicularly up from below, ascending to the glass through the spaces between the balcony railings.
I was much interested watching large numbers of wrens as they crept in and out among the rock crevices during the daytime of April 14th and 15th, and in small numbers on April 16th.
I collected six and could have had more were they needed.
The birds had evidently come some distance. They were tired, very tame and moved about with their feathers puffed out, a sign in birds of incipient exhaustion from hunger.
Of course, there is no doubt that any land-bird which appears on the Tuskar rock, is making a passage.
At high water, the weather need not assume a marked tempestuous state for the rock to become for the major part wave-swept, and I doubt if there is suitable food, even in fine weather, for insect-feeding birds to sustain life for a longer period than a few days.
Meaanwhile, fresh water is not available, this precious commodity being carefully conserved for human use.
Hence small birds never remain long on the rock, but the Tuskar is an excellent observatory for recording the fleeting visits of migrants made during the daytime.
I wish to thank Mr. Glanville, principal keeper, and Mr. Power, his assistant, for ready help in securing me specimens during their hours on watch.
Regarding the wing-power of the wren, It is true that its flight feathers are short, but they are strongly built as is the whole wing.
We find the same holds good in the case of other short-winged birds, many which have heavy body-weight to sustain and yet are excellent fliers when put to the test.
It seems to me that what is most important of all, in considering the migratory flight in birds, is their powers of endurance.
Long pointed pinions are very useful to seabirds, endowing them with buoyancy enabling them to slacken their speed as they survey the waters below for food or to indulge in fantastic aerial gyrations.
But land-birds, whose food is not at hand and whose environment is totally foreign when crossing the sea, are not possessed of, and can manage to dispense with, such wing-faculties.
What is required is the power of flying straight ahead at their accustomed speed, backed by sufficient endurance of wing power to enable them to keep up, and sufficient vitality to enable them to live down the pangs of hunger, thirst and exposure to adverse weather.
Surely the hardy, ubiquitous wren, a denizen even of the bleakest, almost treeless and wind-swept areas of the country where it is as much at home as in sheltered woods and glades, must be accredited with such endurance of flight.
As for speed, anyone who watches a wren dart across an acre of open field will be enabled to estimate for himself what rapid progress could be made in a cross-channel migration by this species.
Structurally the wren is a strongly framed bird, and its wing musculature is in no way inferior in development to that of the smaller warblers of somewhat similar body-weight.
Its reproductive powers are notoriously great, its voice is particularly strong, and altogether physiologically it seems to be a markedly hardy bird.
An interesting feature in connection with the Tuskar migration of wrens which I witnessed is that the two birds obtained in autumn proved to be males, while the ten taken in spring are females.
I wish I had secured more in the autumn to satisfy myself that there is a tendency for the sexes to keep apart when on migration.
The spring evidence on this point seems well worthy of attention.
Another point of interest is that the gizzards of the birds taken at the lantern were quite empty, while those of the birds secured on the rock in the daytime contained, in varying amounts, some insect remains, pointing to the fact that the birds managed to procure something to eat as they perambulated on the rock from daybreak until they were collected.
No comments:
Post a Comment