Swallows: Family Hirundinidae

Family Hirundinidae: Swallows and Martins

Swallows and Martins together make up the hirundines, a family of birds that has spread to almost every continent on Earth except Antarctica. They are all extremely well adapted to aerial feeding, with long pointed wings, short legs and long tail feathers. Swallows tend to have longer, forked tail feathers and Martins tend to have more squared tail feathers. You cannot truly appreciate their aerial abilities until you see them in person. Hundreds of these birds swoop, dive and hunt insects together with a beautiful synchronicity, reminiscent of a school of fish.

Nesting and Breeding

Nesting strategies vary within this family because there is so much diversity, but all Hirundines nest in cavities, often on steep banks. Some genera build their own cavities out of mud on the sides of cliffs or, in more urban areas, the overhangs of a building. Others use cavities on the muddy banks of a river, or the cavity left by a woodpecker. Most often, during the breeding season, the male will select the nesting site and guard it while he attempts to attract a female. Males within this family often use their aerial acrobatics along with their song to attract a female.

But... Can they carry Coconuts?

The video clip above comes from Monty Python and the Quest for the Holy Grail. The movie opens with this scene and the discussion between King Arthur and the castle guard has left me ROFL-ing over and over. While being superbly entertaining, it also contains a very relevant discussion on hirundines. The following is a scientific analysis of this discussion:

1:34-1:47-“The coconut's tropical” “What do you mean?” “Well, this is a temperate zone” “The swallow may fly south with the sun, or the house martin or the plummer may seek warmer climes in winter, though these are not strangers to our land...”

True! Northern Europe is mostly temperate and many temperate species migrate to warmer, more tropical climates in the winter. European hirundines often migrate to sub-Saharan Africa during the winter, while New World hirundines migrate to sunny South America.

1:56-2:07 “It could grip it by the husk” “Its not a question of where he grips it, its a matter of weight ratio. A 5oz bird could not carry a 1 lb coconut!”

True! All members of the passerine order have powerful feet that they use to perch. In fact, when a passerine lands, its feet will automatically grip whatever surface it lands on. Members of the hirundine family often nest on the sides of cliffs and so tend to have specialized muscles and tendons, which allow for a stronger grip than their cousins. They could, conceivably, grab onto the husk of a coconut.

But, members of the hirundine family of passerines are small, sleek birds. They are actually even smaller than the guard tells us, between .35 oz and 2.1 oz. Their ability to migrate such long distances depends on conserving as much energy as possible. In fact, hirundines use 42-78% less energy while flying compared to other birds of similar size. The addition of a coconut, no matter the size would negatively effect their ability to migrate, and the bird would probably not make the flight. No studies have actually attached a coconut to a swallow and tested this hypothesis.

2:13-2:22 “Listen, in order to maintain airspeed velocity, a swallow must beat its wings 42 times every second, right?”

False! A hummingbird does not even beat its wings that many times per second! Flight patterns of the hirundines are unique compared to other birds of similar size. Most small birds fly using a bounding technique, where short bursts of flapping are followed by short periods of time where the wings are actually held against the body. Because their wings are so long compared to their body size, swallows actually intersperse periods of flapping with periods of gliding. This is called undulating flight and is seen more often in large birds. Undulating flight conserves energy and is the most efficient form of flying. While gliding, the bird does not have to expend very much energy. It loses some altitude, but this is made up after a few quick flaps followed by another glide.

2:27- 2:45“It could be carried by an African Swallow” “Oh yeah, an African swallow maybe, but not a European Swallow, that's my point” “Of course African swallows are non-migratory”
True and False! Hirundines that breed in temperate regions do migrate to warmer climates and most species that breed in tropical climates do not migrate. But, some species that breed in tropical climates do make shorter migrations. All swallows fall between 11-17cm in length. If the guard is referring to the sub-family of hirundines, known as the River Martins (Pseudochelidoninae), then he may be on to something. River Martins are found exclusively in Africa. They are slightly larger than the hirundine subfamily, and have stouter legs and bills.