Behaviour and Vocalisations of Nesting Little Eagles
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VOL. 10 (3) SEPTEMBER 1983 73 Behaviour and Vocalisations of Nesting Little Eagles By STEPHEN J. S. DEBUS, PO Box 1015, Armidale, N.S.W. 2350 Introduction Calaby (1951) described in some detail the calls and behaviour of Littie Eagles Hieraaetus morphnoides in the non-breeding season. Fleay (1951) and Cupper & Cupper (1981) described in general terms the behaviour of nesting Little Eagles. Based on information then available, Brown & Amadon (1968) characterised the Little Eagle as a misfit in a genus of otherwise dashing and rapacious eagles. This paper details the behaviour of Little Eagles in the breeding season. Data were obtained in the course of a study on the eagles' diet and breeding biology (Debus, in press). Study area and methods Field "York on the Little Eagle was conducted in the 1980 breeding season at Armidale (30o30'S 151 o40'E) on the Northern Tablelands of New South Wales. Four active nests were observed for a total of 181 hours, distributed thus (hours): incubation period 14.5; downy chick stage 11 ; feathering stage 131.5; post-fledging period 24. Observations were made from about 50 m at ground level, in a hide if necessary, with the aid of a telescope. General observations were made throughout the year with the aid of 8 x 40 binoculars. Data were also obtained from the RAOU Nest Record Scheme. The habitat at Armidale consisted mainly of partly cleared and grazed eucalypt woodland. Hunting behaviour When hunting from the air, Little Eagles employed the soaring and prospecting method (Baker-Gabb 1980). A hunting eagle would soar or glide often at about 40 m (roughly twice tree canopy height), but up to 100m or more. When prey was sighted it poised head-to-wind with wings and tail fanned, carpals held forward and alulae projecting. Attacks to the ground or tree canopy were of variable speed; either fast dive attacks with wing-tips folded to the tail and carpals held out with alulae projecting, or slower drop attacks with the body horizontal and wings and tail spread. Dives were sometimes fast enough to produce an audible rushing noise; both sexes made such dives but males appeared more agile. Standing trees were sometimes used as cover from which to surprise prey at the end of a dive. Two cases of attempted predation were observed at close range. A male eagle made a dive attack into a pine plantation, keeping a tree between himself and his prey until he was within a few metres, at which AUSTRALIAN 74 DEBUS BIRD WATCHER point he pulled out and flew off. The prey was a Brush Cuckoo Cuculus variolosus which had been feeding in the undergrowth and had moved deeper into cover, apparently oblivious of the eagle. A female eagle made a dive attack into the crown of a eucalypt, but emerged immedi ately without prey; Australian Magpies Gymnorhina tibicen, Black-faced Cuckoo-shrikes Coracina novaehollandiae and Noisy Friarbirds Philemon corniculatus scattered in alarm. Elsewhere I have seen a Little Eagle make a sudden stoop through a flock of Little Crows Corvus bennetti which were soaring with it, just missing one. Hunting success was difficult to evaluate from the small number of observations. On one morning a male Little Eagle spent most of the time between 0840 h and midday hunting from the air; during this time he made about six unsuccessful attacks. On some days this pair appeared to be hunting for most of the day before bringing prey to the nest. However, almost half of their 12 observed prey items were delivered by midday. Once another male eagle was seen perched with an empty crop and no prey; he left and returned ten minutes later with a small rabbit. This male delivered prey by 0930 h on eight of 22 observation days, and by midday on two others. On occasions he delivered prey while the nestling was still replete from its last meal. Courtship and advertisement displays Displays took the following forms in apparently increasing order of intensity: Conspicuous perching Little Eagles sometimes perched in prominent pos1t1ons near the nest site. The snowy breast of light phase males was quite obvious when facing the sun; this may have been passive and quite incidental. Perching and calling A loud and excited version of the normal three-note whistling call (Calaby 1951) was repeated many times, interspersed with five or more rapid up-scale notes (i.e. from the finishing pitch of one three-note phrase up to the starting pitch of the next). Both sexes, including incubating females, directed this call at intruding Little Eagles high overhead, and once at a pair of Wedge-tailed Eagles Aquila audax. This type of call was only observed in the breeding season, and appeared to be a territorial call. Soaring and calling Male Little Eagles often soared over the nest site, sometimes p01smg briefly. The three-note call was uttered loudly. A soaring eagle occasion ally made a long, slanting glide ending in a sharp upward sweep or a dive to the tree canopy. Females sometimes soared when not attending the nest. Undulating and calling This was as described by Calaby (1951), except that males generally commenced undulating from a dive rather than a climb; sometimes the VOL. 10 (3) Behaviour and Vocalisations of SEPTEMBER 1983 Nesting Little Eagles 75 final undulations or even whole sequences were performed without wing beating. Males were very agile, sometimes sharply changing or even reversing direction by rolling at the zenith; the latter produced a 'pendulum' effect when repeated. Undulations sometimes ended in a long dive to the tree canopy, with canting of the body about its long axis, producing a zig-zag descent. Once, two males were vigorously undulating and calling at each other along presumed territorial boundaries; such displays were the only action taken by males against intruding Little Eagles. This display was seen at all times of the year, but least often in winter. A female was seen undulating once. The sequence started with a short climb with laboured wing beats, and was less agile and less steep than that of a male, with a smaller amplitude. This was directed at two intruding Little Eagles. Females were twice seen to vigorously pursue an intruder (presumed female by size) until it left. Mutual soaring and rolling Calaby (1951) mentioned mock attacks and 'minor manoeuvres' which were probably the following. Males swept in close above their mates, which rolled and presented talons. Sometimes both tumbled about each other briefly (without contact), meanwhile uttering calls: males, a subdued whining or mewing note at 1-second intervals; females, a shrill piping monotone at 1.5-second intervals, interspersed with a rapid twitter or chatter. This display was seen once in autumn when a female had just acquired a new mate, and many times in the breeding season, often when a female flew up to solicit a soaring male. Behaviour of adults The action patterns described by Ellis (1979) for adult Golden Eagles Aquila chrysaetos were observed in adult Little Eagles. The 'ruffle-shake' comfort movement performed by perched Golden Eagles was occasionally performed by Little Eagles in soaring flight. Diurnal routine Precise details were not obtained, but a broad pattern was noticeable. Little Eagles either perched or flew at low altitudes, with flap and glide flight, early and late in the day unless strong air currents permitted soaring. In the middle of the day they soared or perched. Earliest and latest soaring times noted were: autumn and winter 0930 h and 1630 h; spring 0750 h and 1745 h; summer 0610 h and 1800 h (90 minutes after sunrise and 60 minutes before sunset respectively). The longest soaring time noted was at least 45 minutes, and several other times of about 30 minutes were noted. Little Eagles appeared to spend much of a fine day on the wing. Reaction to disturbance The response of female Little Eagles to human disturbance near the nest was variable, but most were not easily alarmed. Some flushed when the nest was approached within 50 m. Others crouched low in the nest (the 'intruder posture') and sat tight when a person walked beneath it. Some even stayed on the nest when trail bikes were ridden or forestry activities were carried on directly below. A pair nesting in a pine AUSTRALIAN 76 DEBUS BIRD WATCHER plantation had the adjacent two trees felled and snigged out during incubation, yet the young fledged successfully. Interspecific conflict Most of 11 known Little Eagle pairs had nests about 200-500 m from active nests of at least one of the following species: Whistling Kite Haliastur sphenurus, Brown Goshawk Accipiter fasciatus, Australian Kestrel Falco cenchroides, Brown Falcon F. berigora, and Australian Hobby F. longipennis. Some interspecific aggression occurred: the smaller species attacked Little Eagles, Whistling Kites and Little Eagles attacked each other, and Little Eagles attacked Wedge-tailed Eagles. Single birds were involved and no contact was seen. However, a Little Eagle was seen to fly aggressively at a Wedge-tailed Eagle almost head-on, causing the latter to take violent evasive action. Behaviour of nestlings Most of the action patterns described by Ellis (1979) for young Golden Eagles were observed in nestling Little Eagles. One not observed, i.e. wing slapping at intruders at the nest, was described on a nest record card. One nestling was first seen wing flapping and trying to feed itself at about five weeks old. Another was jumping and flapping on the nest at between six and seven weeks old, and both of these nestlings left the nest to hop along the branches of the nest tree two or more days before fledging at about nine weeks old.