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Short-toed Snake-Eagle Circaetus gallicus Scientific name definitions

Jaume Orta, Guy M. Kirwan, and Ernest Garcia
Version: 1.0 — Published March 4, 2020
Text last updated August 30, 2017

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Editor's Note: This is a shorter format account, originally published in HBW Alive. Please consider contributing your expertise to update and expand this account.

Identification

62–70 cm (1); male 1200–2000 g, female 1300–2300 g; wingspan 166–188 cm (1). Large snake-eagle with mid-length tail, comparatively small body, protruding head and long broad wings (1). Plumage rather variable, but not polymorphic and usually rather pale overall; typical contrast of dark head and upper breast with white underparts ranges from very conspicuous (recalling C. pectoralis) to non-existent; brown barring on underparts equally variable. The extent of dark markings below is clearly age-related although not fully documented: the dark head and upper breast is characteristic of adults; birds that are largely white below are immatures (2). Large head with owl-like face; orange-yellow iris (paler in juvenile); 3–4 bands on tail; upperparts mainly greyish brown, generally paler than in C. beaudouini (substantial overlap in non-breeding range in Africa (1) ) and much paler than C. pectoralis (very little overlap in range); present species is unlikely to be confused with another species over much of Eurasian breeding grounds. Female only marginally larger (and longer-tailed) than male, but up to 20% heavier (1). Juvenile similar to adult, but less variable and usually has rufous tone to hood and underparts  markings, plus pale tips to median and greater wing-coverts, and has throat paler than breastband (1).

Systematics History

Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.

Name C. ferox formerly applied to this species, but is unidentifiable. Closely related to C. beaudouini and C. pectoralis; these two frequently considered races of present species owing to claims of mixed pairs in zones of overlap and reports of apparently intermediate specimens, but all direct reports of interbreeding are result of misidentifications of subadult C. pectoralis, while the specimens are all unequivocally assignable to one or other taxon (3). E Asian population formerly treated as a race, heptneri, but geographical variation clinal. Isolated population of Lesser Sundas may be racially distinct; on average somewhat smaller and may have different timing of moult, but little known. Monotypic.

Subspecies


SUBSPECIES

Circaetus gallicus gallicus Scientific name definitions

Distribution
breeds northwestern Africa and southern Europe, north to Estonia, south to the Levant, and east to Kazakhstan, also locally Arabian Peninsula, northern China, and Mongolia; also resident in South Asia (Pakistan, Nepal, and India). Western populations winter in the Sahel (Senegal and southwestern Mauritania to Ethiopia and western Kenya), eastern populations winter in South Asia

SUBSPECIES

Circaetus gallicus sacerdotis Scientific name definitions

Distribution
Lesser Sundas (Lombok, Sumbawa, Komodo, Flores, Besar, Sumba, Alor, Rote, Wetar, Timor, and Tanimbar); reported also eastern Java and Bali, where perhaps only a nonbreeding visitor

Distribution

NW Africa and SW Europe N to Gulf of Finland and E to L Balkhash, NW China and NW & N Mongolia and, in S, to Asia Minor, Levant countries, S Caucasus and W & N Iran; Indian Subcontinent; Lesser Sundas (from Lombok to Timor). W populations winter in Sahel zone of Africa; E populations winter S & SE Asia, some S to Greater Sundas.

Habitat

Varied habitats mainly in warm temperate and tropical zones; from open woodland and even fairly dense forest to semi-desert. Often occurs in areas with mixed habitats: requires fairly open areas rich in reptiles, e.g. stony areas with sparse vegetation cover, pastures, scrub; also, nearly always requires tree cover of some sort, e.g. small woods or scattered trees. From plains and hilly country to mountains; hunts up to tree line and above; in Morocco breeds up to 2300 m, but is mainly found from sea level to 1200 m (1); on Indian Subcontinent, to at least 2000 m (4). Nests in very wide range of woodland types, including both coniferous and deciduous, but winters from desert edge and dry thornbush to well-wooded savannahs (1). Perches on vantage points, e.g. trees, bluffs, pylons.

Movement

Migratory in Palearctic. Generally does not move in flocks but concentrations occur at short sea crossings; sedentary in India , Pakistan and Lesser Sundas . Most migrants winter in tropical N Africa, from S Mauritania (1) and Senegambia to Ethiopia , rarely reaching S to Uganda (1) (Kenyan record recently proven invalid) (5); E birds winter in Indian Subcontinent, occasionally in SE Asia (from Myanmar to S Vietnam and Thailand (1) ). In far E Asia, occasionally recorded on passage at Beidahe, NE China, presumably from poorly known NC China population (6). Exceptional in winter in S Europe, N Africa and Middle East; a few winter in coastal regions of S & E Iberia (7); more common in Arabian Peninsula. Most leave Europe from mid Sept to mid Oct (but overall passage period Aug–Nov (1) ), returning during Mar and first half of Apr (overall late Feb–early May (1) ). Main arrival of adults at Strait of Gibraltar during first half of March (7) but spring passage there is very prolonged, with some immatures arriving as late as June and July (8). Might occasionally oversummer in sub-Saharan Africa, but a Jun record from Central African Republic suggests confusion with C. beaudouini (9). However, immatures move N as far as NW Africa and Iberia to spend the summer (8, 10). Birds gather at crossing points: main route between Africa and Europe passes over Strait of Gibraltar  , with secondary route via Sicilian Channel (1) (though two juveniles satellite-tracked from S Italy moved N then W to cross at Gibraltar (11) ); between Africa and Asia over Gulf of Suez,with C European breeders continuing via W Israel (at least in autumn (12), where maximum 8045 in 1986 (13) ) and the Bosporus (1), with only small numbers moving further E of this route, e.g. through Jordan (14), and numbers taking E Black Sea route not large (15). One satellite-tracked individual migrated from France to Mali, taking one month to complete the journey, moving at an average speed of 135 km/day (overall distance 4045 km); it had an overall winter range of 410 km² (16); another moved further, to Niger, taking 20 days to cover 4685 km (mean 234 km/day), and moved significantly longer distances on days with good weather (17). In European context, has wandered (in both spring and autumn (18) ) N to Norway (18), Sweden (60+ records), Denmark, the Low Countries (1) (occasionally multiple, long-staying individuals (19) ) and SW England (18). Vagrant to Malay Peninsula; also recorded in E Java and is occasional on Bali (1).

Diet and Foraging

Specializes on reptiles, particularly snakes, which constitute 70–80% of prey or more (especially in W & S Europe (1) ). Regional variation in species: mainly non-venomous species, especially Colubridae, up to 150+ cm in length, and usually takes 1–2 mid-sized individuals per day (1). Also takes other reptiles, particularly lizards, including small (1) monitors (Varanus), chameleons, geckos, slow worms and skinks; occasionally mammals, e.g. rodents, shrews, rabbits, hares, hedgehogs; also amphibians; few birds (including nestlings, but mainly sick or injured individuals (1) ) and invertebrates. Probably takes fewer reptiles during bad weather and when recently arrived on breeding grounds. Normally hunts in open areas, but sometimes in dense vegetation; forages at medium height or remarkably high up (normally 20–150 m, exceptionally up to 450 m (1) ), with gliding or soaring flight; to survey terrain more closely, hovers on wind or with wings beating, parachuting down on prey, once located, often with a brief final hover. Also known to still-hunt from prominent perch and even to stalk prey, e.g. amphibians, on ground (1). Swallows snakes and lizards whole, head first; but head may be crushed or torn off prior to consumption, and large snakes can be torn to pieces before being eaten; part of prey sometimes sticks out of bill, when bird already in flight. Smaller prey may be swallowed whole in flight (1).

 

Dietary studies have principally been of prey brought to chicks by adults. Snakes especially are often sizable or large items and so are perhaps especially likely to be brought to nests, smaller prey items being consumed by adults away from the nests, as reported for many and diverse bird species. The possibility at least exists that the importance of non-reptilian prey to this species has been underestimated, considering that in Europe at least reptiles may not always be readily available, especially during inclement or cold weather. Stomach analyses of 14 individuals delivered to recovery centres at the Strait of Gibraltar or killed by wind turbines in that region found invertebrates in seven of them (20). The invertebrates were only found in juvenile or immature birds in autumn and nearly of them were large centipedes Scolopendra cingulata, with up to 44 (and three praying mantises Mantis religiosa) found in a single stomach. The possibility is raised that these were inexperienced or starving birds that took exceptional prey but this need not be the case. Further studies are required to clarify the matter,   

Sounds and Vocal Behavior

Two common vocalizations , both given in flight and perched but almost exclusively in breeding season, are clear whistled “kyo-kyo-kyo” (which sounds less musical and ringing when given by female) and plaintive “mee-ok” (1).

Breeding

Lays in Apr in S Europe and Morocco (where overall season can last to mid Oct (1) ); Apr–May in N Iraq (21); Dec–Feb (1) in Indian Subcontinent (season to May (1) ); young bird in Oct in Lesser Sundas. Aerial courtship displays usually brief and easily missed, though apparently more frequently performs undulating sky-dance (accompanied by much calling) in Indian Subcontinent (1). Males defend territories against intruders, adopting a characteristic threat posture in flight, with head and neck extended, tail slightly raised and legs drooped, while calling repeatedly (22). Nests almost exclusively in trees, rarely very tall, often only a few metres in height; very rarely nests on cliff ledges (once atop a bush on a cliff (21) ); sometimes uses nest of other raptors or corvids. Nest built on crown of tree or on topmost (1) lateral branch, usually 3–6 m above ground, but occasionally up to 25 m (1); tree occasionally on small islands in lakes (15); small for size of species, usually 50–75 cm (1) wide (though up to 100 cm if reused (1) ), 20–25 cm (1) deep; built of sticks and twigs, and lined with green leaves or grass, occasionally even pine needles (23). Pair-bond probably maintained in both migratory and sedentary populations, but new nest normally built each year. One white (23) egg, mean 73·5 mm × 57·8 mm (23); replacement clutch rare; incubation 45–47 days, mainly or entirely by female; chick has white down (both coats, but second is coarser and denser) (23); cared for and fed by both adults; at first given small bits of food, but later learns to pull prey out of adult’s crop, and swallow it whole (by three weeks can swallow 6–9 cm snake whole (1) ); fledging 60–80 days; independent, leaving parents’ territory soon after. Breeding success in C Italy of 0·75 chicks fledged per pair. Oldest recorded bird 17 years old.

Not globally threatened (Least Concern). CITES II. Declined markedly in past, disappearing from most of C & N Europe in 19th century; possibly stable overall by end of 20th century and increasing considerably in W Europe, in Iberia and France (7). In Eurasia, affected very little by pesticides, and generally suffers less from shooting than sedentary raptors, although on Malta, even in 1993, all 50 birds that arrived on a single day were shot. Electrocutions and collision with powerlines (35·%) and killing (22·9%) were main known causes of death recorded by wildlife rehabilitation centres in Spain in 1990–2006 (n = 434 mortalities); cases of killing significantly decreased during this period, but powerline casualties increased (24). Recent decline in numbers wintering in W Africa reported (25). Long-term population trends probably depend on habitat changes resulting from intensification of farming, etc. Estimates in 1980s: 1000–2000 pairs in Spain; 80–100 pairs in Portugal; c. 1000 pairs in France; 380–415 pairs in Italy; perhaps 200 pairs in former Yugoslavia; > 300 pairs in Greece; c. 50–70 pairs in Bulgaria; c. 30–100 pairs in Romania; c. 45–50 pairs in Hungary; c. 20–30 pairs in Poland; over 1000 pairs in Morocco; and more than 200 pairs in Tunisia. Estimates from early 1990s include: 1000 pairs in European Russia; 200–250 pairs in Byelorussia; and sizeable population in Ukraine, where declining due in part to deforestation. Recent censuses, post-2000, indicate a much more favourable situation in Iberia and France; in excess of 10,000 pairs in Spain in 2009–2010 (26) and 2400–2900 pairs in France post-2000 (27). Very few data on Asian populations: perhaps 100–200 pairs in Israel; and 100–1000 pairs in Turkey, although maximum alternatively estimated at c. 8000 pairs; the 12,000 birds seen in Suez in autumn 1984 must correspond to populations occupying E Europe and most of Asia. In Pakistan, widespread and locally quite common, but generally rather sparsely distributed. Status in Lesser Sundas virtually unknown, but very few records, so species almost certainly uncommon, at best; until recently thought to be mere migrant to these islands, but breeding proved in 1971.

Distribution of the Short-toed Snake-Eagle
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  • Year-round
  • Migration
  • Breeding
  • Non-Breeding
Distribution of the Short-toed Snake-Eagle

Recommended Citation

Orta, J., G. M. Kirwan, and E. F. J. Garcia (2020). Short-toed Snake-Eagle (Circaetus gallicus), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.shteag1.01