DEMONSTRATION OF STRENGTH AND CONCEALMENT OF WEAKNESS IN ESCALATING FIGHTS OF MALE SWORDTAILS (XIPHOPHORUS-HELLERI)

In the green swordtail (Xiphophorus helleri) confrontations between st range males regularly escalate to high levels of mutual Bites and Fin Grips, even between males differing greatly in size. The original expe ctation of early game theory models that the behaviours of the ultimat e winners and losers are indistinguishable until shortly before the en d of the fight could not be confirmed. A significant characteristic of loser behaviour is that the Biting rates are higher before and after escalation. Conversely, Fin Grips are more frequent in the ultimate wi nners than the losers. However, such behavioural differences are very poor predictors of the outcome of the fight from the viewpoint of a si ngle fighting individual during the contest. Correct forecasts did not exceed 67 %. The escalating fights of swordtails are considered as tr ials of strength in which the stronger male tries to demonstrate stren gth by the most costly behaviour pattern available, namely Fin Grips, and the weaker male conceals weakness quite successfully by countering with the same tactic and suppressing signs of weakness such as Avoida nce behaviour.