Territory in Bird Life

by Henry Eliot Howard

For the greater part of the year, Guillemots live at sea; singly, in twos or threes, or in small parties, they move upon the face of the waters, extending their wanderings far away from land, out into the broad ocean, where for weeks together they face the gales and heavy seas of the Atlantic. But in due course and in response to internal organic changes, they return, like the Warbler, to their breeding grounds—rocky headlands or islands appropriately situated and affording the appropriate rock formation. During all these months of wandering, the majority seem to ignore the land, to pass away from it altogether, and to spread themselves over the surface of the ocean regardless of mainland or island. Some useful observations, which throw some light on the distance that Guillemots are accustomed to wander from land, were made by Lieut. B. R. Stewart during a number of voyages between various ports in Great Britain and Ireland and ports in North America, principally New York and Quebec. Thus, on the 24th March, large numbers were seen in lat. 55° N., long. 24° W., five hundred miles approximately from land, though on the following day—four hundred miles off Tory Island—they were not so plentiful. Again, on the 1st October, in lat. 53° N., long. 27° W., seven hundred miles or so from land, one bird was seen, whilst on the following day, in lat. 52° N., long. 21° W., a single individual was washed on board by the heavy seas and seemed little the worse for the adventure. Within two hundred miles of the west coast of Ireland, he found them plentiful on various occasions. From this it is clear that the circumstances under which the bird lives for many months in succession must impose a considerable strain upon its constitution; and how it is able to withstand the buffeting of wind and water, to secure its food, and to endure, is a mystery. It is important, therefore, that the young bird should be properly nourished and protected from anything that might harm its constitution, and important, too, that the parents should be freed from any undue strain during the course of reproduction.

The conditions which the breeding station has to fulfil are threefold: in the first place, it must be in proximity to the food-supply; secondly, it must provide the necessary shelter for the egg and for the helpless offspring; and, in the third place, it must be so situated that the young can reach the water in safety. We will examine these conditions one by one.

The proximity to the food-supply is a consideration of some importance. The life of the Guillemot during the winter is a strenuous one; we know that large numbers succumb in stormy weather, and we can infer that slight constitutional defects might make all the difference between failure and success; and, therefore, the less severely the constitution of the parent is taxed during reproduction, and the more securely the constitution of the offspring is built up, the greater prospect will both have of resisting the hardships of the winter successfully. Much, then, will depend upon the distance the parents have to travel in order to obtain food. The farther the breeding station is removed from the feeding ground the greater the physical strain which will be imposed upon the birds, and the greater the chance will there be of the offspring being improperly nourished. Now the food consists of small fish, largely of sand-eels, which are secured in deep water, and the abundance of which varies, possibly according to the nature of the currents. Hence cliffs which are situated away from the water, or from which the water recedes at low tide, or which are surrounded by an area of shallow water, and are thus not in proximity to the feeding ground, even though they may fulfil the second and third condition, will not answer the requirements of a breeding station.

Of no less importance is the type of rock-formation. Not every formation affords the necessary ledges upon which the egg can be deposited with safety—the face of the cliff may be too smooth, or too jagged, or the shelves may run at too acute an angle. Many of the large assemblages of Guillemots in the British Islands are found where the rock is quartzite, mica-schist, limestone, or chalk. The reason of this is that such rocks are weathered along the planes of stratification, of jointing, of cleavage, or of foliation—the strata being probably of unequal durability—with the result that innumerable shelves, ledges, and caverns, which are taken advantage of by the birds, form a network over the face of the cliff. But only those ledges can be made use of which are placed at a considerable height above the water, because, when the cliff faces the open sea, the lower ones are liable to be washed in stormy weather by the incoming swell and thus become untenable. There is a small cove in the midst of the most precipitous part of the breeding station at Horn Head, wherein the shingly shore shelves rapidly to the Atlantic and faces to the west. Here, towards the end of July, young Kittiwake Gulls can sometimes be found washed up on the beach—some living, but in every stage of exhaustion, others dead, and in every stage of decomposition; here is the young bird, recently caught by the swell and thrown upon the shore, lying side by side with the remains of others that had previously succumbed to starvation—on every side evidence of the devastation wrought by the Atlantic. May not some of this destruction have been brought about by the nests having been placed upon the lower ledges within reach of an exceptionally heavy sea? Hence much depends upon the nature of the rock-formation, and many a mighty precipice, even though it may fulfil the first and third condition, is nevertheless valueless as a breeding station.

Finally, the young bird must occupy a ledge from which it can reach the water in safety. There is much difference of opinion as to the manner in which it leaves the ledge, but all agree that it does so before it is capable of sustained flight. If, then, the face of the cliffs were made up of a series of broken precipices, or if the rocks at the base projected out into the water, or if detached rocks abounded in the waters beneath, the mortality amongst the chicks would no doubt be considerable.

The coast-line of Co. Donegal will illustrate the foregoing remarks. On the southern and western side of the Slieve League promontory there is no real Guillemot station; only on the northern side—the quartzite in the vicinity of Tormore—are the birds to be found in large numbers. Northwards from here, a wild and rugged coast is passed over before other stations are reached—at the eastern end of Tory Island and on Horn Head; and beyond this, to the east, there are none, not even on the old rocks that form the promontory of Inishowen. Why, we ask, do countless numbers crowd the ledges of Horn Head, whilst they are absent from the precipices of Slieve League; why, too, are they absent from the granite cliffs of Owey? The reason is not far to seek. Either the face of the cliff is made up of a series of broken precipices, or the face of the precipices is too smooth, or the otherwise suitable ledges are situated too near the water, or the water recedes from the base of the cliff at low tide. Many miles of rock-bound coast are thus useless for the purpose of reproduction.

Now when we bear in mind how large an expanse of coast is formed of blown sand or of rocks of low altitude, and how many miles of cliff fail to supply the three essential conditions that we have been considering, we can see that suitable breeding stations must be limited both in number and extent. From a wide expanse of ocean hosts of individuals are therefore obliged to converge at certain definite points; and hence, each recurring season, there must arise a competition for positions at the station, just as there is competition between individual Buntings for positions in the marsh. And the ability to obtain a position upon a suitable ledge involves, in the first place, an impulse to search for it; in the second place, an impulse to dwell in it; and in the third place, an impulse to resist intrusion upon it. It would be useless for an individual to be pugnacious if it had no fixed abode; equally useless for it to establish itself on a particular ledge if it had no power to defend it—all of which implies an inherited nature similar to that of the Bunting. But the proximate end to which the competition is directed is not alike in the case of both species. In the case of the Guillemot it has reference solely to the piece of rock whereon the egg is laid; in the case of the Bunting to a piece of ground capable of furnishing an adequate supply of food for the young; and the reason for the difference is this, that there is always an abundance of food in the water beneath the cliff, but breeding stations are scarce, whereas there is always an abundance of situations in the marsh in which the Bunting can place its nest, but the supply of food varies and at times can only be obtained with difficulty.

If then the Guillemot were to behave after the manner of the Bunting and assign to itself a portion of the face of the cliff, or if it were only to occupy a few ledges, or an even lesser area—a single ledge—what would be the result? That it would attain to reproduction is beyond question; that the egg would be safely deposited there can be no manner of doubt; neither is there any reason to suppose that the offspring would not be successfully reared. But, indirectly, its behaviour would affect the Guillemot race. For if it be true, as the crowded ledges certainly seem to show, that there is a dearth of suitable breeding ground, no greater calamity could befall the species than that some members should exercise dominion over too large an area of the habitable part of the cliff and thus prevent others from breeding. Under such conditions the race could not endure, since in this, as in every case, its survival must depend upon a close correspondence between the behaviour of the individual and the circumstances in the external environment.

Scarcity of suitable cliffs is the principal reason of the ledges being so closely packed with Guillemots, just as it accounts for this part of the precipice being crowded with Kittiwake Gulls, that part with Herring-Gulls, and that part again with Razorbills and Puffins. Yet each individual preserves its few square feet of rock or soil from molestation, and the area each one occupies varies according to the conditions of existence of the species. Thus the Herring-Gull occupies a comparatively small area, although one many times larger than that of the Guillemot. It requires more space than the latter, owing to the fact that it not only builds a nest but rears four instead of a single offspring, and it can be allowed this, because, since its young remain in the nest until they are capable of sustained flight, it can make use of many miles of cliff from which the tide recedes at the base, or which have, at their base, rocks jutting out into the sea; but manifestly it cannot be allowed so much space as the Bunting.

Martins build in close proximity to one another, owing probably to shortage of accommodation, and, in their case, the nests have to be so situated as to be sheltered from the wet. If water drips upon them for any length of time, the mud, of which they are composed, crumbles and large pieces fall away, with the result that the eggs or the young are precipitated to the ground. Consequently, not every house or perpendicular cliff will answer the purpose of a breeding station. A few pairs build their nests beneath the eaves close against the walls of my house, and year after year the result is much the same; after every downfall of rain, the water collects into rivulets, trickles down over the eaves, is absorbed by the mud and destroys the nests. Thereupon, the birds set to work and rebuild; but again the nest is destroyed, and again they rebuild, and so on throughout the summer, and only on rare occasions do they succeed in rearing offspring at the proper season. Similar conditions must prevail in many situations; but, clearly, the more binding and plastic the building material, the longer the nest will withstand the action of the dripping water and the greater chance will there be of the young being reared in safety. Observe, therefore, how far-reaching an effect so small a detail as the nature of the mud can have upon the status of the species in any given locality. Where the conditions are favourable, there the birds must congregate to breed, and, like the Guillemot, if each individual exercised dominion over too large an area, the species as a whole would suffer.