Barn swallows

a complicated society

I like to go up around the Mendenhall Glacier Visitor Center for lots of natural history reasons, and one of them is to watch the barn swallows that nest in the pavilion, the bus shelter, on the sides of the center itself, and sometimes on the kiosk. The insect-catching adults swoop high and low, sometimes playing ‘chicken’ with the numerous cars and buses, which typically exceed the posted speed limits. Most of the thousands of tourists are oblivious to these birds, but a few do pay attention.

In mid July, some of the nests had big chicks, either just leaving the nest or just about to do so. Other pairs still had eggs, in some cases because vandals had destroyed their first nests and these pairs had to begin anew.

Photo by Bob Armstrong

Originally, barn swallows nested in caves, cliff crevices, and hollow trees, but now they have converted to using human structures almost entirely. They build inside culverts, under bridges, and on buildings; use of natural sites has become unusual and noteworthy. Historically, as North American became more populated by humans, barn swallows also spread into new areas.

Barn swallows occur all over the northern hemisphere in the nesting season (but migrate to South America or Africa in winter), and they are among the most intensively studied songbirds. European birds have white breast and belly feathers, but in North America these feathers are rusty orange. It turns out that in North America, a dark rusty breast on a male is attractive to females, and females mated to dark rusty males produce more chicks than those mated to paler males.

In this species, the elegant tail is long and forked, and males have longer tails than females. A deeply forked tail is said to increase lift and allow tighter turns, and if the fork is symmetrical, maneuverability is enhanced. Long, symmetrical tails develop on males that have few external parasites. Females really go for males with long, symmetrical tails—the best fliers with the fewest parasites. So males with such tails have a high probability of getting a mate, they get better mates, and they indulge in more extracurricular copulations as well. Females that are socially bonded to short-tailed males actively seek extra-pair copulations with better-endowed males.

However, those studly males with big tails don’t invest much time and energy in the chicks of their ‘official’ mate: they’re too busy running around. The short-tailed males are more attentive fathers; they also reportedly build better nests, and females are also more attentive moms when they have better nests. So there is some compensation to females for not being mated to the studliest guy. But the nests of short-tailed males often contain some other male’s chicks, so the short-tailed males end up investing effort in chicks that are not their own.

If all that were not enough complexity, barn swallow nests are sometimes subject to hostile takeovers by intruding males. The marauding male may belong to another species, such as a wren, or house sparrow, or cliff swallow. And sometimes the intruder is another barn swallow. If the intruder pushes out the original male, he generally destroys any eggs or small chicks, and then mates with the widowed female.

Nests are built of pellets of mud, cemented to the wall or beam, and lined with grass and especially feathers. Both parents incubate the eggs, although only the female has a featherless, highly vascularized brood patch on her belly. Incubation takes about two weeks and chicks are in the nest roughly three weeks. After leaving the nest, the juveniles are tended by their putative parents for about two more weeks. Chicks in a second brood are sometimes also tended by older siblings from the first brood. Parents (and older sibs) can recognize their fledglings, not by voice, but by variation in plumage color patterns on the chest—no two chicks are exactly alike.

Barn swallows nest in several locations in Juneau and are easily seen. Next time you see one, just think a moment about how complex their lives are.



…jacks of all trades

A black-billed magpie harassing a hawk owl. Photo by Bob Armstrong

Juneau sees magpies in fall, winter, and early spring, outside of the nesting season. They come to us from nesting areas in the Interior. They are not strong fliers, but that long, elegant tail allows them to make quick changes of direction. These flashy birds sail across the roadways, check out roadkills and dead salmon, raid some kinds of bird feeders, and fossick about the edges of wetlands and woods in search of something edible. Magpies can eat ‘most anything, be it animal or vegetable. Sometimes they pick ticks from the hides of moose and deer. They eat fruit, catch mice, and gobble up beetles and worms, regurgitating the indigestible bits in pellets. When an eagle holds down a salmon on the shore, magpies team up to rob it: one magpie tweaks the eagle’s tail feathers, while another one snags a chunk of salmon.

These are black-billed magpies (Pica pica). The species is currently considered to comprise about twelve subspecies, spread across much of the northern hemisphere. The North American subspecies nests in the dry, cool parts of the West, geographically isolated from the other subspecies. There are other geographically isolated subspecies—one in northeastern Siberia, one in extreme northwest Africa, and one in (of all places!) a small mountain range in Saudi Arabia. All the others are found in Eurasia, from the UK and Scandinavia southeastward to south China and Thailand.

Some ornithologists think that black-billed magpies may have inhabited North America long ago, before the last major glaciation. They got wiped out, perhaps by environmental changes associated with glacial advances. They then recolonized our continent, coming from Asia over the Bering land bridge.

Down in the valleys of southern and central California lives another species, the yellow-billed magpie (P. nuttalli). These birds may constitute a relict population left over from a time before the last major glaciation. They are quite different the black-billed species in life history, physiology, and social behavior. Despite all the differences, yellow-bills are thought to be more closely related to North American black-bills than those black-bills are to the Eurasian forms. It may turn out, with more study, that the North American black-bills are really different species than the Eurasian ones, which have quite different behavior and vocalizations.

Magpies form pairs that are ostensibly monogamous, but extra-pair copulations occur (as in many other songbirds), especially involving older males. They do not defend large, multi-purpose territories, but only defend an area around a nest. Our magpies like to nest in trees and large shrubs, but prefer to forage in open country. They build large, domed nests of sticks and line them with mud and grass. It can take six to ten weeks to build this structure—no small investment! Both male and female work on the nest, the male mostly with sticks and the female mostly with the lining.

The female lays an average of about six eggs (but up to nine) and incubates the eggs for about eighteen days; the male brings food to her as she sits. Incubation begins before the last egg is laid, so hatching is not synchronous and the chicks are therefore of different sizes. Chicks stay in the nest, fed by both parents, for about four weeks. There is strong sibling competition for food, and when food is scarce, the smaller chicks may starve (or be killed by bigger chicks). As a result, the number of fledglings per nest can be markedly smaller than the number of eggs.

After the chicks leave the nest, they are fed by the adults for six to eight more weeks, and sibling rivalry continues. When they become independent, the juveniles (especially males) generally form winter flocks, with a strong dominance hierarchy.

Females mature at age 1 year, males usually at age 2 years. But average life expectancy is not great: females 2 years, males 3.5 years. So, on average, each bird only gets about two nesting seasons and thus two chances to rear young.

Magpies belong to the corvid family, along with ravens, crows, and jays. Many of the corvids, including magpies, have a fascinating behavior known from only a few other animals (such as elephants). They conduct what are called ‘funerals’. If a magpie dies, the first bird to notice the body calls in other magpies, and they all gather around the corpse for a short time. A bit like conducting a wake in human society, although the exact function of these funerals is not known.