Parental care by males, part 2

these are not deadbeat dads!

This essay will consider male parental care in birds and mammals. Both birds and mammals evolved from reptiles, and some ancient reptiles did have parental care by at least one parent, but modern reptiles have no record of male parental care, so they will be ignored here. As is true for fishes and amphibians, the factors that govern the evolution of patterns of parental care are no doubt several and still subject to debate and future research.

Biparental care is the usual thing among birds: both parents tend the young in over ninety percent of bird species. Females often do the incubating of eggs, but her male may feed her while she does so and the males generally help feed the chicks. This is the case for American dippers, for instance; as one of my field techs said, during our intensive study of this species: there are no dead-beat dads! In fact, we even know of one hard-working dad who raised at least a few of his chicks by himself, after his mate disappeared. The emperor penguin male goes a step further: he incubates a single egg on his webbed feet while his mate goes off to sea and feed; then they both tend the chick.

In some taxonomic groups of birds, including hummingbirds and grouse, females generally do all the work while the males run off to find more females. But even in these groups, there are unusual species in which both parents provide parental care; the willow ptarmigan is a local example.

Still more unusual are avian species in which males both incubate and tend chicks by themselves. Here a few examples. Spotted sandpiper females often lay one clutch of eggs and leave it to the male to do the incubation and guarding while she proceeds to lay another clutch (with the same or a different male) that she incubates and tends; this is a pattern found in several shorebirds.

Spotted sandpiper nest–is this tended by the dad? Photo by Katherine Hocker

In two of the species of kiwi in New Zealand, the Australian emu, and several other species, males incubate and tend the chicks alone. The cassowaries of Australian and New Guinean rainforest also have hard-working males, who incubate the eggs for weeks and then tend the chicks for months. They are fierce defenders of their little families: One day in the Australian rainforest I encountered a cassowary family; we were all looking for fallen fruits. Imagine looking up from the forest floor and seeing a very large bird, almost as tall as you and with claws that could rip you open, glaring at you from just a few short yards away. You can bet I apologized for my presence most abjectly and discretely retreated rather quickly!

What about the mammals? Virtually by definition, females are the ones that feed the infants, and lactation is considered to be the single most expensive thing a female mammal ever does. Dependence of the infants on mother’s milk means that females are always involved in parental care, so uniparental care by males is not an option. Biparental care is not common, but males are reported to be closely involved with parental care in about five percent of all mammal species. The best known cases include carnivores and primates, but regular male care occurs in other groups too. Here are some examples:

Among the carnivores, the males of foxes and wolves regularly bring food to their young. Asian raccoon dog males participate in all forms of parental care except lactation, and also tend the female during the birth process. Male members of packs of African wild dogs bring food to lactating mothers and young pups.

Male baboons and macaques carry babies around, which may help protect the infants from predators or intruding strangers. However, this situation is more complex than that, because the male may obtain direct benefits too: a male with a baby in his arms suffers less aggression from other males and may also gain favor with the infant’s mother. And if there is a fight between males, the infants are in great danger. In some small New World primates called tamarins, including the cotton-top tamarin, males regularly carry and care for babies. Males of the endangered pied tamarin reportedly do most of the parental care except for lactation.

Wild horses and zebras live in groups, often a male’s harem of females plus foals. Males defend their foals and females from predators.

It’s a rare herbivore that helps feed the young ones, but male beaver do: they regularly help build winter caches of branches on which the whole family, but especially the still-growing young ones, feed; they also help maintain dams that make the pools that protect the lodge and facilitate transport of branches. They stay with the rest of the family in the lodge over the winter, interacting and providing body warmth. Among the smaller rodents, males of the California deer mouse reportedly brood the young, keeping them warm until they can regulate their own body temperature. Prairie vole males cache food, brood and groom the babies, and even retrieve them if they wander out of the nest.

Granite Basin denizens

visiting the world of marmots and spotted sandpipers

A long, lazy lunch, which we enjoyed while sprawled on a huge boulder in the noontime sun: we basked like lizards—or, more appropriately for our locale, like marmots.

Soon thereafter, we were whistled at—by a pair of baby marmots that had just recently begun to emerge from the den where they were born. These toddlers tried very hard to sound the alarm about the ‘monsters’ tramping along the creek, but their whistles sounded very raspy and feeble. That didn’t deter them, however, and they shrilled every few seconds until we were well past their rock.

It seems to take a while for youngsters to learn how often to ‘cry wolf’. Adult marmots would probably not have gotten quite so excited at the sight of two-footed monsters traipsing by. Interestingly, baby beavers behave much the same way, tail-slapping over and over again at something strange, often ignored by their parents, until they learn to tailor their alarms to the circumstances.

A young hoary marmot

The scientific name of our hoary marmot is Marmota caligata. The second name refers to boots, because the marmots’ black feet reminded some taxonomist of that footgear. Farther south, hoary marmots typically inhabit high elevations, with other marmot species at lower altitudes, but in our area, these marmots range from sea level to the alpine zone.

These marmots have a very flexible mating system. Some mate in pairs, or social monogamy; a study in south-central Alaska suggested that this was the common arrangement there. Others are polygynous, two or more females socially bonded to a male. Sometimes an extra male resides on the periphery of a mated male’s territory. Regardless of the social arrangement, however, there is reportedly a lively scene of extracurricular activity. Males go gallivanting over the hillsides, looking for receptive females. And they find them: many litters have been shown to have multiple fathers. So perhaps the two we saw were just half sibs.

Gallivanting males are most common in big patches of suitable habitat, where several colonies of marmots are neighbors. Small habitat patches may only support one family group and opportunities for gallivanting are fewer. Males reportedly behave more parentally when gallivanting is not an option; they guard their offspring more assiduously and even play with them.

Hoary marmots typically mature disperse from their natal territory to find their own place in the world when two years old. Mature females, age 3 or more, can produce a litter every year if food is very abundant but often skip a year or two if food is scarce. Mating occurs in spring, soon after the adults emerge from hibernation. Gestation lasts about four weeks and the pups are weaned after roughly four more weeks. Litters usually consist of about three pups, but pup mortality can be high, especially during winter. Litter size and frequency of reproduction varies with the social mating arrangements: monogamously mated females produce larger litters more often than bigamously or trigamously mated females, which are more likely to skip a year—and whose males do more gallivanting in the females’ off-years!

I heard but failed to see a spotted sandpiper near the pool at the top of the falls at the basin entrance. Spotties are found there virtually every year. They usually nest on gravel bars and upper beach fringes, and the basin provides several gravel bars.

Spotted sandpiper females arrive first on the breeding ground and claim a territory. Males arrive later and set up their own territories inside those of females. Some females mate monogamously, and both parents may care for the eggs; this mating arrangement is more common among younger females. Older females are commonly polyandrous: a female often mates with two or even three males in succession. She lays a clutch of four eggs for Number 1 and leaves him to do all the incubation and chick-tending, while she goes on to Number 2. If there is no Number 3, a female may help Number 2 care for the brood.

Photo by Bob Armstrong

Some polyandrous females bond with males within her original territory. Others search widely for a second mate. It turns out these females keep track of their neighbors and they know which territories previously have been successful in producing chicks. And to the males on those territories go the females to find a sire for their second broods. In this case, it seems to pay to be a nosy neighbor!

The plot thickens still further! Those second males may indeed perform all their parental duties and also may be helped by the female if it is her last brood of the season. But second males are not necessarily the fathers of the chicks. In some cases the female stores sperm of Number 1, which becomes the father of at least some chicks in the second brood. In effect, Number 2 has been cuckolded by the first male and ends up caring for another male’s chicks.