A bird that breaks all the rules

THE red-necked phalarope is a colourful little wading bird, which used to breed in Ireland.

A few pairs still do so in Britain, although their numbers are declining.

It’s a bird which breaks all the rules. Individuals, for example, can be extraordinarily tame; parents have been known to brood chicks held in the hand. Like other waders, phalaropes head for warmer climes each autumn but not to sheltered European estuaries. Instead, most head for the Arabian Peninsula to spend the winter in the Indian Ocean, feeding on plankton. Waders don’t swim but phalaropes are an exception; their toes are lobed to help them do so.

These, and a few other creatures, have very strange lifestyles and why they behave the way they do has long puzzled scientists. Now a team from the Universities of Sheffield, Bath and Veszprém in Hungary believe they have found the answer. The peculiarities, they claim, stem from an excess of males in the population.

Male birds, normally, are more elaborately plumaged than their mates. They secure territories and defend them against rivals. Attired in a glamorous outfit and singing his finest love songs, a male persuades a female to join him. Gifts of food during courtship help her form eggs which he will fertilise. She usually makes the nest. In about 54% of species, both sexes incubate. In 24%, the female sits alone while in 6% the male does so.

Daddies, generally, assist in feeding the chicks. In species which produce a second brood, the father may take over the rearing of the first one but, with birds generally, mammy does the lion’s share of the child-rearing and domestic chores.

In the phalarope world, things are very different. The female is bigger than her mate and has the brighter plumage. As the breeding season approaches, she chooses a location close to open water and begins advertising for a mate. Although phalaropes are not very territorial, she will ‘see off’ rivals approaching her pool. Encountering a prospective partner, she swims around almost begging him to mate with her. Males being such wimps, she has to do so repeatedly; ‘faint heart never won fair lady’ is not a phalarope maxim. Once seduced, he copulates with her several times a day. When the four eggs have been laid, however, she absconds, leaving incubation and chick-rearing entirely to him. She may even seduce a second male, setting him up on another nest.

Such a scenario is most unusual among birds. There are, however, similar instances elsewhere in the animal kingdom.

The most extreme examples occur among seahorses which, despite appearances, are not crustaceans but fish. In their case, even pregnancy is transferred to the daddy; she deposits her eggs in a ‘brood pouch’ on his abdomen. He nurtures them alone until they hatch. This happens at night and the male is ready to receive another batch of eggs next morning. That dad should be left holding the baby seems a travesty of the ‘natural order’ but the system provides a faster through-put.

András Liker and Tamás Székely, who study the behaviour of shore birds, have published their results in Nature Communications. The crucial factor in sex-role reversal, they believe, is that there’s an excess of males over females in the species involved. In a normal regime, with enough females to go around, a male could afford to ‘play the field’.

By impregnating a female and having her raise the offspring, he is free to pursue other partners and indulge in extra-marital flings. In this way he stands to maximise the number of offspring he fathers which, after all, is what his life is all about. With phalaropes, however, there is a shortage of females and he must stay close to his mate until the eggs are laid, lest she be impregnated by other males. Then, the best way to ensure that his genes survive is to protect the nest; with no prospect of other dalliances, he takes over the show.

The authors also discuss the influence of sex ratios on homosexual behaviour and cooperative breeding, topics which, however, need further research.