Ardea
Official journal of the Netherlands Ornithologists' Union

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Kruijt J.P. & Hogan J.A. (1967) Social behavior of the lek in Black Grouse, Lyrurus tetrix tetrix (L.). ARDEA 55 (3-4): 203-240
This paper presents data gathered in four spring seasons of observations at two Black Grouse leks in the northern Netherlands. Behaviour of males among each other, of females, and courtship and mating are described. Roughly two-thirds of the approximately 12 males attending each lek were territorial; the remaining males were non-territorial. Territorial males defend geographically fixed areas, varying in size from 100 to over 4,000 square meters. Territories remain highly constant throughout the spring and fairly constant from season to season. All territorial males have access to their own territory only and trespass only under special circumstances; on the lek they are therefore by definition of equal rank. Territorial males can be classified roughly as central and marginal males. The former tend to have smaller territories at the centre, are more continuously present on the lek, display less frequently outside the lek, and show a higher frequency of aggressive behaviour than marginal males. Non-territorial males are called the intruders because they frequently enter the ground of territorial males where they are usually chased off; they are therefore considered to be lower in rank than territorial males. Most, though not all, intruders are juvenile males. Intruders attend the lek irregularly; when present, they may show all the same fighting, threat, and courtship patterns as territorial males. By persistence an intruder may establish a new territory at the edge of the lek; two such cases are described. Females start to visit the lek regularly in April; most of the mating takes place in the second half of April, usually around the time of sunrise. When a female visits a territory, the owner courts her by squatting at a distance and by circling her, which may lead to copulation. Neighbouring males attempted to interfere in more than one third of the observed copulations, but this leads only rarely to actual disruption of the mating. During their visits to the lek, females walk from territory to territory and have a strong tendency to stay together in groups. Tentative crouching in response to courtship of the males may occur in several territories and many times within one territory. Females often terminate crouching and withdraw at the moment that a male attempts to mount. By crouching long enough a female allows a male to mount and mate; in this way she exerts her choice. Females sometimes mate more than once during a visit; in one case a female was observed to mate with 2 different males. Analysis of landing and visiting distributions show that females prefer central territories at the peak of the season. More than 85% of the copulations was performed by central males; the remaining by marginal males. Factors underlying the preference of females for central males are discussed. The choice of the female is possibly influenced by the greater density of males in the centre and by the tendency of central males to show more mutual interactions and better tactics during their courtship. The annual periodicity of lek display is discussed briefly; it appears that Black Grouse males visit the lek during most of the year. Some results of experiments with stuffed models are described.


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