BEHAVIOUR, SYSTEMATICS, AND NATURAL SELECTION

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  • 318 SYSTEMATICS : A. J, CAIN IBIS 101

    ses iambes & pieds, sont noirs ressemblgts B ceux d'vne Cane, et les yeux rouges. grande corpulence qu'vne Cane. Linnaeus, 1758. (Anasferina)

    Elle n'est de si

    ferina. 27. A. alis cinereis immaculatis, uropygio nigro. Faun. svec. 107 Anas fera fusca. Gesn. av 116. Aldr. o m . 1. 19. c. 40. Will. orn. 288. t . 72. Raj. av. 143. Habitat in Europae man'timis.

    Alb. av. 2. p . 87. t. 98.

    Willughby and Ray, 1678.

    D. 221. The Poker, or Pochard, or great read-headed Wigeon: Anas fera fusca of Gesner, Aldrov. t. 3 .

    Cane a la teste rouee of Bellonius. Penelops veterum & Rothalss of Gemer. Aldrov. 218. - That we described weighed thirty 6vo ounces: From tip of Bill to end of T d was nineteen

    inches long, to the Claws points twenty one. It is bigger than the Common Wigeon, and for its bigness shorter and thicker. The lesser covert feathers of the Wings, and those on the middle of the back are most elegantly variegated with dark brown and cinereous waved lines [or ash-coloured, with very narrow, waved, cross, dusky lines!. The Rump and feathers under the Tail are black, so that the Tail is compassed with a ring of black. The lower part of the Neck is likewise black, so that the forepart of the body seems also to be encircled with a ring or swathe of black. The Head and almost the whole Neck are of a deep fulvous or red colour: the middle part of the Breast white, the sides and lower part and Belly all of the same colour with the Back, and varied with the like transverse undulated lines, but both colours paler: Toward the Vent it is by degrees darker coloured. The Tail is very short, not exceeding two inches, made up of twelve feathers, of a dark grey, the outmost the shortest, the rest gradually longer to the middlemost; yet the excess is not considerable, so that notwithstanding it is not to be reckoned among those that have sharp Tails. The quits of the Wings are about twenty five, all of one colour, viz a dark cinereous, though if they be carefully heeded, there will appear some diversity, for the tips of the exteriour and greater feathers are marked with black, of the middle ones with white. The interiour bastard-wing and lesser covert-feathers of the underside of the Wings are white.

    The feathers divide the middle of the upper Mandible coming down from the forehead in form of a peak or acute angle. The upper Mandible is of a lead-colour, but its tip black: The nether is wholly black. The Irides of the Eyes are of a very beautiful colour, from yellow inclining to a sparkling red: The Feet lead-coloured: The mem- branes connecting the Toes black: The inmost toe the least, having a membranous border annexed to its outside.

    The characteristic note of this Bird, is one uniform colour of its Wings, without any feathers of different colour in the middle of the Wing, as is usual in most Birds of this kind.

    In another Bird of this kind (which we take to be the Female of this) the Bill was black with an ash-coloured spot of the form of a crescent a little above the tip. The back feathers and coverts of the Wings had no such transverse waved lines as those of the Male. In other points it agreed most- what with the Male.

    The Bill is bigger and broader than in the Wigeon.

    The back toe hath likewise an appendant membrane or fin.

    BEHAVIOUR, SYSTEMATICS, AND NATURAL SELECTION

    N. TINBERGEN (Department of Zoology and Comparative Anatomy, University of Oxford)

    Several review articles have been published recently on the general topic of behaviour, classification, and evolution (see J. M. Cullen 1959, Hinde 1959, Lorenz 1958, Roe & Simpson 1958). The present paper will therefore deal with a slightly different subject, and discuss, with some selected examples, the extent to which behaviour differences between taxa must be assumed to be due to natural selection. Some questions of method will also be raised. While most examples will be taken from birds, some data on other animals will also be given.

    THE TAXONOMIC USE OF BEHAVIOUR CHARACTERS

    It will be useful to consider first which behaviour characters can be used for taxonomic and systematic purposes, how they can be used, and what exactly are the phenomena which require an evolutionary explanation.

    Analysis of behaviour " machinery ". to the taxonomist.

    It is now almost a commonplace to say that there are behaviour characters helpful Mayr (1958) has given a useful review.

  • 1959 SYSTEMATICS : N. TINBERGEN 319

    Behaviour always involves complicated machinery ; the sequence of events leading to a certain behaviour usually involves sensory reception; it always consists of an extremely complicated series of internal events involving the nervous system and often other systems, and it ends in coordinated muscle activity. As the analysis of this machinery proceeds (and it does with increasing speed) the characteristics of species, or taxa of any level, can be described in increasing detail. Today behaviour characters of many different kinds are known. The most striking of these, and hence the best known, are motor patterns, particularly those of the fixed pattern type, which can be seen directly and described without elaborate analysis. Many investigations deal with differences or similarities between two or a few species. Thus Morris (1954) described how the Song Thrush Turdus philomelos differs from the Blackbird Turdus mmula in its ability to smash shells of snails; Klomp (1954) described differences in the way Lapwings Vanellus vanellus and Black-tailed Godwits Limosa limosa move their feet in walking. There are now also a number of more comprehensive reports, dealing with many species of a group (see e.g. Crane 1941, 1957 on fiddler crabs, Uca ; Hinde 1955 on finches, Fringillidue ; Lorenz 1941, 1958 on ducks, Anatinae ; Tinbergen 1959 on gulls, Luridae; for more references see Hinde & Tinbergen 1958); and these more extensive studies also concentrate mainly on motor patterns.

    We also know something about inter-taxa differences in responsiveness to stimuli; thus the Sparrow Hawk Accipiter nisus and the Goshawk A. gentilis, while hunting in much the same way, select different prey (Lack 1946); the alarm call of the Kittiwake Rissa tridactyla is not very different from that of other species of gulls, but it has a much higher threshold to stimulation by predators (E. Cullen 1957); the courtship of the males of Drosophila simulans responds to visual stimuli to a larger extent than the males of the related D . melanogaster (Manning 1959) ; the Oystercatchers Haematopus ostralegus of the Faeroes show distraction displays more readily than those of the mainland (Williamson 1952); British Starlings Sturnus vulgaris respond to day-lengthening earlier than continental Starlings (Bullough 1942).

    Other behaviour characteristics concern some property of the internal machinery ; naturally reports on such characters are scarce and fragmentary. Beach (1958) concludes from comparative studies of androgens and their effects on reproductive behaviour that the responsiveness of target systems rather than the chemical composition of the hor- mones has changed in vertebrate evolution; Vince (1956) describes differences in ability to haul up food by means of a string between Goldfinches Carduelis carduelis and Chaf- finches Fringilla coelebs; Armstrong (1952) reports that the Shetland Wren Troglodytes troglodytes zetlandicus is monogamous in contrast to the polygamous wrens in more southerly latitudes.

    The tendency to learn is in many species confined to certain situations or internal conditions, and these too may be very different in different species. The feeding behaviour of Honey Bees Apis mellifica can be conditioned to some but not all the scents which their sense organs can receive (von Frisch 1956). Kittiwakes have no tendency to respond selectively to their own young, which other gulls learn to do in a few days (E. Cullen 1957). Several species of gulls smash shells by dropping them from the air; the same behaviour is shown by Carrion Crows Corvus corone; but unlike crows gulls very rarely learn to drop them over a hard substrate, although they are capable of many feats of learning, such as learning to select updraughts over hilly country, which helps them to travel along convenient flight lines under varying wind-conditions (Tinbergen 1953 a). Honey Bees condition themselves to feeding sites by performing a locality study ; Bumble-bees Bombus spp. do this onlywith certainflowers, not with others (Manning 1956). As I will argue below, the study of such behaviour characters is not only important for its own sake, but, because many characters are functionally interrelated, the student of evolution has to extend his studies over as many characters as possible.

  • 320 SYSTEMATICS : N. TINBERGEN IBIS 101

    True and apparent behaviour characters. Behaviour is known to be subject to phenotypic change to a much greater extent

    than morphological characters. Learning processes may even keep changing the behaviour throughout the life of the individual. It is therefore of special importance, when dealing with behaviour characters, to investigate whether observed differences are genetically determined or merely reflect differences in the environment. Although phenotypic changes may foreshadow genetical changes, as long as an observed difference is merely due to environmental effects it is not a true difference and therefore does not offer an evolutionary problem. Several instances are known of species-specific dif- ferences which are induced by the environment and are species-specific only because the environment is constantly different for the two species compared. The selective responsiveness of Turnstones Arenaria interpres to the ala