Histrionicus histrionicus Harlequin Drakes sparring over females at LeHardy Rapids, Yellowstone River, YNP 5-26-10.
This species spends most of the year in the salt and then comes inland to high mountain rushing streams to breed and raise their broods returning to the salt as soon as the broods are reared.
Nice to see Jim. Males can do at least two things to get more matings- compete with other males or attract females. These two sexual selection pressures tend to cause males to be larger than females (to help them with male-male competition), and males to be more brightly coloured than females (to attract mates). There are some exceptions to this "rule" such as occurs with phalaropes (referred to as "reverse sexual dimorphism").
Good points John. In this particular instance there were 5 males and 4 females in the group and one male was very busy trying to impress each of the females when he had an opportunity. The four females appeared to be closely associating with four of the males, swimming together, resting on the rocks as pairs and foraging as pairs. The lone male would approach and in each case the male of the pair would attack.
As a Biologist working in the Pacific Northwest for nearly 40 years I have always been impressed by Harlequins and this was one of the largest groups I have encountered away from the salt.
Stay away from my girl!
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