France and I were just in Cape May, NJ, looking for a particularly colorful strain of Jersey Boys. My first ecoregion birding blog was from this same area of the Northeastern Coastal Forests Ecoregion (NA0411), which extends the entire length of the New Jersey coast. That was in the spring; this time was a frigid winter day.
We were looking for male Purple Sandpipers, Jersey Boys in the sense they regularly winter up and down this coast. Purple Sandpipers (Calidris maritima) breed in rocky areas of the far northern tundra and winter uncommonly along rocky coasts of the eastern US and Canada (as well as in Europe). Most shorebirds sensibly winter in the balmy tropics; Purple Sandpipers are notable for being the shorebird species that in eastern North America winters the farthest to the north. They are pretty hardy and if you want to see them, you have to brave the elements!
We found some nice Brant and an elegant male Gadwall. Red-throated Loons and Common Loons seemed to be equally common. Rock after rock was devoid of Purple Sandpipers.
Finally, success! We found one small group on a rocky jetty at North Wildwood, NJ, a lifer for me. Try as we might, we could not see the slight purple gloss on their winter dress, that gives them their name. They do have striking orange legs.
As it turns out, its pretty well impossible to tell the difference between males and females, so I’ll just have to assume it was the guys we found hanging out. Why my interest in the boys? Purple Sandpiper males are really fascinating in the bird world. In almost all bird species (and mammals for that matter), females disproportionately invest time and energy in producing an egg, or a baby, and so it makes sense for them to be the better parents – they have a lot more to lose than the father, who typically has not invested much energy in his procreative duties. Purples are the opposite – the males take on the heaviest workload incubating and then once the eggs hatch, it is pretty well 100% Dad-only on duty to raise the chicks. The female invariably deserts the territory immediately after the eggs hatch.
A male gender bias in parental care is unusual in the bird world, but when so, it is often because the species is polyandrous – where the females have multiple male partners. In jacanas for example, the female will mate with numerous males and lay eggs in multiple nests. Obviously she cannot look after all of them, so the males are the primary caregivers. In yet other species, males will invest in parental care but only if they also have behaviors that help guarantee their paternity – such as aggressive guarding of females to prevent extra-pair copulations.
None of these explanations work in this case. Purple Sandpipers are remarkable in that they are highly monogamous – males and females are faithful to each other, with pair bonds often lasting for many seasons. Extra-marital flings are almost unknown. Females after deserting do not go on to find a new mate and start a second clutch. Females furthermore are not inherently bad mothers; if the male dies at the time of hatching, she steps in and raises the young and does so just as competently as the male. Studies in Norway have uncovered a lot of this startling evidence and of course it would have to be in Norway – always way ahead of the rest of us in gender equality…
So in the complex gender politics world of birds, why has this arrangement evolved? There must be an advantage for males to provide uniparental care, for females to desert their families so consistently, and yet for this unusual arrangement to not get in the way of meaningful long-term relationships.
There’s quite a few theories out there but none seem very convincing. Ornithologists are not Purple Sandpipers, and they don’t understand everything that is going on in their world. We basically just don’t know, and this is not an easy species to study in their remote breeding areas. The next time you are on a rocky headland up in the High Arctic Tundra Ecoregion of Baffin Island, sit and watch for a few seasons, and you may figure it out.
By the way, on this weekend we also spotted one of the original and most colorful Jersey Boys. Great fun to take in a Frankie Valli concert at Atlantic City’s Borgata Casino — 82, still singing and going strong! And finally, since today is March 8, happy “A Day without a Woman Day”!
Glad to hear your trip with France was superb with a successful lifer spotting and a concert. You guys know how to do it right!
Indeed interesting post-reproduction behaviours for these birds. Obviously I’m not a bird biologist however, I wonder about your comment that male birds don’t invest as much energy in procreative duties. In my mind male birds invest an unbelievable nutritional investment in growing elaborate feather displays and then performing amazing courtship dances and rituals to attract a female. Then they defend their territory with enormous expenditure of physical energy, flying, flapping, patrolling, chasing and singing. All the while the female sits! On eggs albeit. If it wasn’t for this madness on the part of the males, we would not be birders. Then they molt all these colourful feathers and have to re-grow new feathers for the remainder of the year – more energy requirements. Not sure if all bird species, male and female, molt every year part of pest cleansing.
So that takes me to your next comment about the heaviest workload is incubating. They are just sitting on the eggs in the nest after all. Now once the eggs hatch, yes, the work truly begins.
At this point if the Purple Sandpiper male dies, several days after hatching, then the female abandons the nest. However, she will raise the little ones at the time of hatching if dad dies. That’s interesting. I immediately think that this is one smart mama purple sandpiper. Definitely her energy investment is growing 3-4 eggs and then laying eggs is admirable, after which dad takes over incubating. If he dies during incubation or very shortly after hatching she does not waste her energy investment and raises the chicks. BUT if the dad dies several days after hatching, she “knows” he was either weak (couldn’t find enough food for him and offspring) or careless (got eaten by a predator). Clearly, would you want your offspring to carry weak and careless genes? No. So she abandons the hatchlings. Smart eh?
Wonder where exactly the females go while the males are feeding chicks? IF the most unusual biology of these birds is their choice of wintering grounds, a northern rocky coastline, maybe she heads out to that coastline in late summer and early fall to fatten up before the winter months. She definitely has to make it through the winter to grow and lay eggs next spring! And the male supports her needs and hangs back to raise the chicks. Fun to speculate. Thanks Doug, your investment in time and energy is appreciated – gets me thinking and I like that.
Excellent questions and comments. Nothing like a mother’s point of view! They are medium-sized shorebirds, about the size of robins. She lays 3 to 4 eggs.
The limited studies that have been done seem to show that indeed, she does definitively leave the breeding territory as soon as the eggs hatch – both she and the male tend to return to the same site each spring so it will probably only be in the following year they will see each other again and resume their monogamous relationship – maybe that long break in the winter from each other is what keeps the pair bond strong?! She will only take care of the chicks if the male vanishes at or before hatching (this has been shown by experimentally removing the males at different times). So if the male dies a few days after hatching, the young will not survive.
The theory that she is too exhausted for these duties is one that makes intuitive sense and has been tested. But it doesn’t seem to be true since for all the nests where she had to take over duties, she seemed to do just as good a job as the male and was as likely to return the following year, indicating no immediate impact on her survival. However, it is a possibility that her lifetime fitness (her survival over many years) might be affected; that would require observations over many years to figure out. If so, that might explain the evolution of her behavior, but the driving force behind the evolution of the male’s behavior remains obscure.
Really interesting. Photos wonderful Doug. How big is this bird? How many eggs does she lay?
My considered opinion (being a mother) is this: After nest building, developing and laying eggs, she is so exhausted that she is not able to dash around finding food. .She goes off for R and R. She is probably not very far away (has not deserted the nest) and is observing the male and keeping a wary eye out. In the case of the male dying, she has to take over as she cannot allow her babies to die. The advantage is that those babies are always well looked after until fledging.