The parental roles of purple sandpipers.

Purple sandpipers (calidris maritima) are a small wading shorebird. They overwinter along all of Norway’s shoreline (and other places around the Atlantic coast), are a year-round resident in Northern Norway, and breed as high north as Svalbard.

And, as I learned in the research I read this week, their sex roles during breeding season are quite unique.

Gender roles of the purple sandpiper

The egg incubation duties are shared more or less equally, but around hatching time, the female leaves the area until the next breeding season, and the male is the one taking care of the young.

When that happens with shorebirds, it’s typically because the female has multiple clutches with multiple partners. However, purple sandpipers are monogamous, the female leaves the area completely without breeding again, and, they might actually be chased away by the guys, rather than abandoning the nest.

The papers

• Sex roles in the monogamous Purple Sandpiper Calidris maritima in Svalbard by Elin P. Pierce
• Why don’t female purple sandpipers perform brood are? by Elin P. Pierce, Lewis W. Oring, Eivin Røskaft, Jan T. Lifjeld

At first, the female spends most time on the egg.

During the first part of the incubation period (the period when birds sit on their eggs), the female purple sandpipers spend most of the time on the nest.

Purple sandpipers breed asynchronous, meaning not all of them start breeding at the same time. While one couple is sitting on eggs already, neighbors may still be arriving. Fights for territory are still common at this point, so it can be useful for the males to spend more time defending the territory in the start, before picking up half the load when things have calmed down.

The male’s reserves may be lower at the start of the incubation period too, because they’ve just used a lot of energy defending or establishing their territory at the start of the mating season. So it can be beneficial for the males to spend more time foraging so they can rebuild their strength before spending more time sitting on the eggs.

Both male and female are equally good parents.

Researchers wondered if the male was the one looking after the chicks because they were better at protecting them from predators, or because the female sandpipers were weakened after using a lot of energy on the eggs.

So one breeding season, they removed the male from a set of nests right around hatching time, the females from another set of nests, and compared them to “untouched” couples. And what they found was quite interesting: male and female purple sandpipers were equally good parents.

They attended to their chicks for the same amount of time as males, showed similar responses to predators, and were just as successful at raising at least one chick to fledging. The chicks raised by female sandpipers gained weight at similar rates than those raised by the males, and the weight loss amongst the adults was similar too.

Potential advantages for the males to stick around.

The male purple sandpipers might get several advantages by sticking around and taking care of the young.

They can prevent other couples from taking up this area, which reduces the chance of territorial conflicts the next year. Additionally, female purple sandpipers are very faithful to their breeding sites, regardless of the male.

So by sticking around they can keep the territory, and by keeping the territory they keep their mate.

Spending more time on the breeding grounds also gives the males the chance to “advertise” themselves to potential future partners, since there’s no guarantee their current one will survive the winter.

Abandoning nest or being excluded?

This could mean that female sandpipers abandon the nest not because they want to, but because they physically get excluded from the area.

Something that supports that theory is that male purple sandpipers have been observed chasing their female away from the nest after hatching.