Sunday, June 16, 2013

An All-American Dipper Dad

(Fathers' Day special edition)

"[H]is music is that of the streams refined and spiritualized. The deep booming notes of the falls are in it, the trills of the rapids, the gurgling of margin eddies, the low whispering of level reaches, and the sweet tinkle of separate drops oozing from the ends of mosses and falling into tranquil ponds." (John Muir, writing on the songs of the American Dipper)

American Dipper (c) John Ashley
Male American Dipper waiting for dawn
Four a.m. on a wild and free mountain stream. It's dark, and it's cold.

He's standing silently, motionless on a rock, and surrounded by a watery roar as the cool-blue night turns towards morning. Father's Day is dawning for a Dipper dad (Cinclus mexicanus).

The male Dipper roosted overnight in the protection offered by a stone overhang, but he was never out of hearing distance from his nest. He left his roost at first light to perch on this rock. Here he waits in motionless silence for dawn to arrive, when he will resume his namesake dipping motion and begin foraging for breakfast to feed his growing family.

In spring and early summer, his world shrinks to a short stretch of stream near the nest, a well-disguised ball of moss and grass that hangs from a nearby cliff face. Inside, his mate incubates their eggs for two weeks and, after they hatch, broods their young for another week or so to keep the naked chicks warm until they grow a coat of insulating feathers.

Dipper dad delivers most of the food that the female eats during incubation and early in the brooding period. As their chicks get older, she joins her mate in delivering food to the nest.

Male American Dipper (c) John Ashley
Male American Dipper making a food delivery 
When the Dipper family is about two weeks old, and the young just barely fit inside their domed home, the parents reduce the number of food deliveries to the nest. This behavior encourages the hungry - and still flightless - chicks to jump from the nest and join the adults along the stream, where the parents continue feeding them for another two weeks.

After the chicks fledge, a small percentage of the Dipper parents divide their family and territory. The male and female separate for a while, and each raises a chick or two on different stream reaches. But most Dipper families on Montana streams stay together while tending to their youngsters.

If their territory includes enough food and nesting sites, some females even start a second nest attempt while the Dipper dad is still feeding teenagers. If they manage to raise at least one brood together, then chances are high (more than 80%) that in mid-winter the same female will rejoin the same male on their breeding territory.

Most Dippers are solitary through the fall and early winter. In Montana, Dipper dad initiated pair formation back in December, two months before overt courtship began. It started with the two birds feeding near each other and slowly turned into courtship feeding, where the male presents food to the female as she crouches and flutters her wings like a nestling. As the bond grows stronger, the pair begins acrobatic pre-nuptial flights up and down the stream for up to 10 minutes at a time, with the male flying just an inch or so behind the female.

Dipper dad also sings to her throughout this courtship. He stretches his neck out, raises his bill skyward, and droops his wings while strutting and singing in front of her for 20-30 seconds at a time. The female studies his performance from a nearby rock.

If his courtship and singing is enough to win her over, then Dipper dad finds himself waking up on Fathers' Day with a nest full of eggs or young chicks. And after their chicks leave the nest, Dipper dad starts singing again - but this time, it's not for mom.

Around this time of year, Dipper dads (and moms, too) start singing to their youngsters. Dippers are mostly quiet while tied to the nest, so they don't attract the attention of potential predators. But the singing returns around 6-12 days after their young leave the nest.

After each food delivery, Dipper dad stands 1-2 feet away, turns sideways to the juvenile and sings for an average of 8 seconds, then flies off to find more food. The female sings to her young half as often, but for for twice as long, so their totals average out. This "post-feeding song" behavior teaches Dipper songs to the young birds during a sensitive learning period.

It's a repertoire of wild birdsong that we can also enjoy whenever we visit our free-flowing streams, starting around Fathers' Day.