African Wildlife & Environment Issue 78

BIRDING

One pair bred for many years close to the Howick Falls in a large Eucalyptus tree which eventually died, and the nest collapsed over time. More recent breeding activities have been recorded from Zimbali Golf estate near Ballito Bay. Regular reports of sightings also come from the Pafuri area, of the Kruger National Park, where birds are often spotted in the riverine forests and picnic sites.They are also seen around Punda Maria camp and towns like Tzaneen, where a few pairs breed in the extensive forests above the town. For many years, birds could be often seen calling and displaying above the town itself. Some biologists consider this species highly intelligent, cautious, independent, and inquisitive when compared to other accipitrids. Breeding Crowned Eagles have one of the most prolonged breeding cycles of any bird. It is common for raptors that live around the tropics to have a relatively elongated breeding period. Crowned Eagle pairs breed once every two years; a single breeding cycle is approximately 500 days in duration. Most other eagle species complete a breeding cycle in under six months, or in about 35% of the time it takes the Crowned Eagle. While the incubation and nestling stages are about average for a tropical eagle (for example the Black-breasted Snake-eagle Circaetus pectoralis , about half the weight of this species, has an incubation/nestling cycle of a similar length). It is the extraordinary post-fledging period of nine to 11 months that makes the Crowned Eagles' breeding cycle so long. During this post-fledging period, the young bird remains close to the nest (200-300m). Breeding can occur almost year-round throughout the range, although egg-laying seems to peak roughly around the end of the African wet season or the early dry season, i.e. from July to November. Territories or home ranges are maintained vigorously. In Zimbabwe, individual home ranges can vary from 140 to 200 km2 in size. Near the city of Nelspruit in South Africa, home ranges averaged 30 km2 in size. In southern Africa, the mean distance between active nest sites can range from 2 to 19.5 km. Adults seldom forage more than 10km from the nest.

The eagle is highly vocal and has a noisy, undulating display flight. In Equatorial Africa, they often call year-around, while elsewhere they may vocalise mainly to the context of breeding and nesting activities. Displays consists of a series of steep dives, and ascents, with a few wing-flaps at the top of each climb, and descending circles, usually and figures of eight. During descents, eagles can drop as much as 60 m at a time before circling back up. During this display, the male is noisy, uttering a shrill "kewee- kewee-kewee" while throwing his head back, often calling for a spell of approximately 30 seconds. The female’s call is a lower pitched and mellower "kooi-kooi-kooi-kooi". The displaying male may reach heights exceeding 900 m, sometimes even near cloud level at over 2,000 m above the ground.The adult female may also perform independent display flights, uttering the lower "kooee-kooee-kooee" sound. The female seems to display less often. Pairs also perform visually striking mutual displays, sometimes arising from the first type or when the pairs come together after a brief absence. Despite the spectacular and conspicuous nature of their display flights, the Crowned Eagle is sometimes considered a 'clumsy' flier out in the open, lacking the grace and speed attributed to other eagles in a high-flying context, such as large Aquila species. While awaiting food at the nest, both the female and the young call out a penetrating, high "kwee-kwee-kwee", that can border on incessant. In disposition, the Crowned Eagle is considered nervous, constantly alert and on edge. Ironically, considering their otherwise hyperactive behavior, the main hunting techniques of the Crowned Eagle require long periods of inactivity, spent sitting on a perch, where they are virtually invisible. Mature Crowned Eagles are reportedly nearly fearless towards humans and, unless shy from prior interactions, are unusually inclined to treat humans aggressively. They can nest around developed areas, including in the vicinity of quiet suburban, developed areas (such as in view of apartment or office buildings), so long as prey is abundant and accessible, and the habitat provides enough mature vegetation to facilitate nest building and hunting activities.

43 | African Wildlife & Environment | Issue 78 (2021)