Stresemann's bushcrow

Appearance

The Stresemann's bushcrow is about 28 centimeters long and weighs 130 grams. The genders look similar and are not sexually dimorphic. Overall it is pale grey with a black tail and wings. The head, mantle, scapulars, back, rump, and uppertail coverts are all a pale grey. The feathers on the forehead, upper ear-coverts, and throat fade into white. The bright azure skin around the bushcrow's eye is featherless and can be inflated, narrowing the blackish-brown eye into a slit. The feathers behind the eye are capable of moving to reveal an oblong pink patch of skin. The bird's black beak decurves into a sharply pointed tip and is relatively small for a corvid. This beak is 33 to 39 millimeters long. The feathers on the bird's chin are fine and can form a small tuft when erected. The bushcrow's breast and flanks are pale grey, fading into white on the rear flanks, belly, and undertail. On the wings, the lesser and median upper-wing coverts are grey, while the rest of the wing is a slightly glossy blue-black. Its blue-black tail is relatively long and square-ended. Its legs are black. When the plumage becomes worn, the upperparts appear to have a brownish tinge. The juvenile Stresemann's bushcrow is slightly duller than the adult, and the feathers of the body and upperwings are fringed with creamy-fawn. The facial skin, bill, and legs are also a dull grey.

Distribution

This species is endemic to central-southern Ethiopia. It lives in a small area circumscribed by the towns of Yabelo, Borena, Mega, and Arero in Sidamo Province, and settles in wildlife under protection within Yabelo Wildlife Sanctuary and Borana National Park. Its total range covers about 2,400 square kilometers.

Behavior

The Stresemann's bushcrow is normally found in groups of about six birds. This species does not migrate.

The bushcrow is a very vocal species, particularly when foraging. Its main contact call has been described as a single metallic "kej". While flying, the species frequently calls out a nasal, rapid "kerr kerr kerr". While these are the most frequent vocalizations, several others are known. Allopreening adults utter a metallic "kaw, kaw, kaw". Foraging birds call out "how, how, how", a single, quiet "quak", and a soft, repeated "guw". While building its nest, the bushcrow is known to utter a low "keh" sound, and adults utter a deep "waw" while rubbing their bills together.

Habitat

The Stresemann's bushcrow lives in flat savanna covered with mature acacia and "Commiphora" thornbushes. The bird prefers open short-grass savannas with scattered stands of these mature thornbushes. The soil must be deep and rich to support the bushcrow. It is most numerous when these stands are next to agricultural fields. For many years it was unknown why the species could be completely absent from areas of suitable habitat near seemingly identical but inhabited land. However recent research has revealed that the bird appears to inhabit an area with a very precise average temperature extreme, all of the seemingly suitable but uninhabited surrounding lands actually have a slightly higher average temperature that appears to prevent the birds from successfully colonizing. It is also not found near the scattered broadleaf woodland made up of "Combretum" and "Terminalia". Its habitat is between 1,300 and 1,800 meters above sea level.

Reproduction

The Stresemann's bushcrow nests either alone or in a small, loosely connected colony of three to five nests. It is monogamous and may form a lifelong pair bond. The bushcrow occasionally has a third bird, or in rare cases two to four more, help the breeding couple both build the nest and care for the young. The helpers may also not be restricted to helping one nest at a time, as they have been seen at nests across the loose colonies. Allofeeding and allopreening, where the birds feed or preen each other, takes place both between the pair and with the other bushcrows in the colony. The bushcrow lays its eggs shortly after the first rains, which normally occur in late February and early March, leading to its eggs being laid in late March and early April.

The nest is an untidy globular structure, on which the roof tapers to a point that has an opening into the interior chamber. The nest is 60 centimeters in diameter while the interior chamber is 30 centimeters across. To start constructing the nest, a single twig is inserted into the top of an acacia tree 5 to 6 meters above the ground. This leads to the paired bushcrows becoming excited, engorging their blue facial skin. Almost ritualistically the pair then pick the acacia's leaves and twigs, dropping them to the ground. The pair end this display by chasing each other through the trees before continuing construction. The nest is made out of thorny twigs while the interior chamber is lined with dry grass and dried cattle dung. Damp soil is used to keep the initial twigs connected. Old nests are repaired and reused.

Up to six eggs are laid in the nest. The bushcrow's eggs are cream-colored with pale lilac blotches that concentrate into a ring at the wider end.

Food

The bushcrow feeds both on the ground and in trees. It begins foraging at sunrise. While foraging, a bushcrow can be alone, in a pair, or in a group of six or seven other bushcrows. A foraging bushcrow digs vigorously in the soil while its beak is held slightly open to catch any insects it unearths. When it catches something, it carries it to the nearest tree or bush, pins it down with its foot, and kills and eats the prey. This species has also been seen using its beak to tear apart rotten wood and inspecting cattle dung in the search for food. It may also land on the backs of cattle to search for parasites. It can also chase flying insects, which it does on foot, abruptly changing direction and taking flying leaps after its prey. It often mixes with white-crowned starlings, red-billed hornbills, red-billed buffalo weavers, and superb starlings while foraging. When hunting in the trees, it is capable of walking atop horizontal branches and jumping upwards towards the crown, then descending in a glide from the crown to the ground.

It eats primarily invertebrates and specifically insects, including termites. Larvae and pupae, especially of "Coeloptera" moths, are eaten as well as the adults.