Ruff - Behaviour - Mating

Mating

Males display during the breeding season at a lek in a traditional open grassy arena. The Ruff is one of the few lekking species in which the display is primarily directed at other males rather than to the females, and it is among the small percentage of birds in which the males have well-marked and inherited variations in plumage and mating behaviour. There are three male forms: the typical territorial males, satellite males which have a white neck ruff, and a very rare, recently discovered variant with female-like plumage. The territorial males, about 84% of the total, have strongly coloured black or chestnut ruffs and stake out and occupy small mating territories in the lek. They actively court females and display a high degree of aggression towards other resident males; 5–20 territorial males each hold an area of the lek about 1 m (1 yd) across, usually with bare soil in the centre. They perform an elaborate display that includes wing fluttering, jumping, standing upright, crouching with ruff erect, or lunging at rivals. They are typically silent even when displaying, although a soft gue-gue-gue may occasionally be given.

Territorial males are very site-faithful; 90% return to the same lekking sites in subsequent seasons, the most dominant males being the most likely to reappear. Site-faithful males can acquire accurate information about the competitive abilities of other males, leading to well-developed dominance relationships. Such stable relationships reduce conflict and the risk of injury, and the consequent lower levels of male aggression are less likely to scare off females. Lower-ranked territorial males also benefit from site fidelity since they can remain on the leks while waiting for the top males eventually to drop out.

Satellite males, about 16% of the total number, have white or mottled ruffs and do not occupy territories; they enter leks and attempt to mate with the females visiting the territories occupied by the resident males. Resident males tolerate the satellite birds because, although they are competitors for mating with the females, the presence of both types of male on a territory attracts additional females. Females also prefer larger leks, and leks surrounded by taller plants, which give better nesting habitat.

The behaviour and appearance for an individual male remain constant through its adult life, and are determined by a simple genetic polymorphism. It was originally thought that the difference between the two types of males was due to a sex-linked genetic factor, but in fact the genetic locus relevant for the mating strategy is located on an autosome, or non-sex chromosome. That means that both sexes can carry the two different forms of the gene, not just males. The non-territorial female does not normally show evidence of its genetic type, but when females are given testosterone implants, they display the male territorial behaviour corresponding to their genotype. Territorial plumage and behaviour are inherited as recessive characteristics.

Although satellite males are on average slightly smaller and lighter than residents, the nutrition of the chicks does not, as previously thought, influence mating strategy; rather, the inherited mating strategy influences body size. Resident-type chicks will, if provided with the same amount of food, grow heavier than satellite-type chicks. Satellite males do not have to expend energy to defend a territory, and can spend more time foraging, so they do not need to be as bulky as the residents; indeed, since they fly more, there would be a physiological cost to additional weight.

A third type of male was first described in 2006; this is a permanent female mimic, the first such reported for a bird. About 1% of males are small, intermediate in size between males and females, and do not grow the elaborate breeding plumage of the territorial and satellite males, although they have much larger internal testes than the ruffed males. This cryptic male, or "faeder" (Old English "father") obtains access to mating territories together with the females, and "steals" matings when the females crouch to solicit copulation. The faeder moults into the prenuptial male plumage with striped feathers, but does not go on to develop the ornamental feathers of the normal male. As described above, this stage is thought to show the original male breeding plumage, before other male types evolved. A faeder can be distinguished in the hand by its wing length, which is intermediate between those of displaying males and females. Despite their feminine appearance, the faeders migrate with the larger 'normal' lekking males and spend the winter with them.

The faeders are sometimes mounted by independent or satellite males, but are as often "on top" in homosexual mountings as the ruffed males, suggesting that their true identity is known by the other males. Females never mount males. Preliminary research results suggest that the faeder characteristics are genetically controlled by a single dominant gene. Females often seem to prefer mating with faeders to copulation with normal males, and normal males also copulate with faeders (and vice versa) relatively more often than with females. The homosexual copulations may attract females to the lek, like the presence of satellite males. Not all mating takes place at the lek, since only a minority of the males attend an active lek. As alternative strategies, males can also directly pursue females ("following") or wait for them as they approached good feeding sites ("intercepting"). Males switched between the three tactics, being more likely to attend a lek when the copulation rate the previous day was high or when fewer females were available after nesting had started. Lekking rates were low in cold weather early in the season when off-lek males spent most of their time feeding.

The level of polyandry in the Ruff is the highest known for any avian lekking species and for any shorebird. More than half of female Ruffs mate with, and have clutches fertilised by, more than one male, and individual females mate with males of both main behavioural morphs more often than expected by chance. In lekking species, females can choose mates without risking the loss of support from males in nesting and rearing chicks, since the males take no part in raising the brood anyway. In the absence of this cost, if polyandry is advantageous, it would be expected to occur at a higher rate in lekking than among pair-bonded species.