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It is easy to assume that most non-humans conform to a basic breeding model. Boys court girl, most impressive boy wins girl, he passes on his genes and then he may or may not stick around to help rear any young. However, the natural world doesn’t always stick to this parenting strategy. A minority of species exhibit what we might think of as the reversal of ‘traditional’ gender roles. And some of the best-known examples of this kind of role reversal come from one of my favourite groups of birds, the waders. Let’s meet some of these female waders.
Playing the Field
The UK has tiny breeding populations of two such waders: the dotterel and the red-necked phalarope. These migratory species take gender role reversal to its extreme. In many bird species, males are brighter and more colourful than females, who are often plain and inconspicuous. Dotterel and phalarope females, though, are more boldly marked than the males. This is a clue to the way these females take the lead when it comes to reproduction.
Once back on the breeding grounds, red-necked phalarope females will chase males and fight other females over them. This is what we’d usually expect to see from the males when it comes to courtship. Once a successful female has bagged her man and laid 3-4 eggs, she may well find another male and repeat the process, producing multiple clutches in a season. Crucially, she plays no part in egg incubation or chick rearing, leaving it all to the male.
Likewise, dotterel females take on what we might see as the more traditional male role. They will lay two or three clutches to different fathers, a system known as polyandry. This refers to a female mating with multiple males in a season, as opposed to polygyny, where a male will mate with many females. Dotterel females then leave the males to it and have been known to move on to different breeding grounds to mate again, even as far away as Norway.
Other waders that behave in this way include the jacanas, a family that lives across the tropics. The spotted sandpiper (a North American breeder) is also polyandrous, although females and males look similar.
Left Holding the Baby
A number of wader species show elements of gender role reversal, without going the whole hog. Purple sandpipers and knot both winter in the UK. The sandpipers are found on rocky shores, often in the company of turnstones. Knot prefer muddy shorelines and estuaries and are famous for forming large groups in winter. Both migrate north to breed.
On the breeding grounds, males and females of these two species look pretty much identical and once paired, birds remain monogamous during the season, meaning they won’t mate with other birds. Both sexes incubate the eggs, although males probably do the lion’s share.
Once the eggs have hatched, though, the females of both species usually leave the male to it. They will start their migration south while the male tends the chicks. Although the young are what is known as precocial, so can feed themselves almost immediately after hatching, dad will look after them until they fledge, defending them from predators. Snowy plover females, breeding in the Americas, will also sometimes desert the nest in this way once the eggs hatch, leaving males to parent alone.
A Scientific Conundrum
Scientists have been puzzled for a long time about why some species swap gender roles. The assumption has largely been that for most creatures, it is logical for females to invest all their energy in rearing young because they have already put lots of energy into producing eggs. Essentially, it would make no sense not to see the process through after all that effort.
A University of Sheffield study of 18 different wader species, though, may have some answers to why not all animals conform to this pattern. Comparisons suggested that when there were more males than females, gender reversal was more likely. This could be because with more competition for fewer female waders, the chances of mating more than once are small for males. This makes it worth putting everything into one brood. Females, on the other hand, increase their chances of producing more young by mating with multiple partners.
It could be that female waders from monogamous species who leave males to rear young once hatched do so to improve their own chances of surviving to breed in subsequent years. The longer they stay on the breeding grounds, the more vulnerable they are to predation, after all.
Whatever the reasons behind these different breeding strategies, it is clear there is no one size fits all in nature. What works for one species may not for another. And these female waders show that sometimes, just sometimes, it is the female of the species who gets to wear the trousers.
Shorebirds in Action is a comprehensive look at the behaviour and lives of over three quarters of the world’s shorebirds and waders, covering everything from breeding to migration and moulting.
Waders can be tricky to identify in the field, partly because at different ages and times of year, they have different plumages. Waders of the Northern Hemisphere is a great resource for for anyone in Europe and North America wanting to get to grips with the waders they might see.