Australian Falcons: Ecology, Behaviour and Conservation

By Stephen Debus

Falcons are stunning and iconic birds. Australia has six falcon species, with two endemic to the continent and two others endemic to the Australasian region. They are important indicators of the health of our ecosystems, due to their position at the top of the food chain. But several species are declining, with two species threatened in some states.

In Australian Falcons: Ecology, Behaviour and Conservation, Dr Stephen Debus provides a 30-year update of knowledge on these six species, as well as a falcon-like hawk, the Black-shouldered Kite. This book is based partly on the author’s field studies, as well as being a supplement to the Handbook of Australian, New Zealand and Antarctic Birds (HANZAB) and recent global treatises. It offers up-to-date information on the Australian species, including their behaviours, ecology and biology. It reviews their population status and threats, and suggests what needs to be done to ensure the future of these spectacular birds.

Australian Falcons is an invaluable resource for raptor biologists, birdwatchers, wildlife rescuers and carers, raptor rehabilitators and zookeepers.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Nov 2, 2022
• ISBN: 9781486315789

Stephen Debus

Dr Stephen Debus has studied Australia’s raptors, including falcons, for over 40 years. He is an honorary research associate in zoology at the University of New England. He is the author of Australasian Eagles and Eagle-like Birds, Australian Birds of Prey in Flight and Birds of Prey of Australia (CSIRO Publishing), and was awarded BirdLife Australia’s D.L. Serventy Medal for ornithological publication.

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Introduction

Recent DNA studies have revealed that falcons are not, after all, related to the other diurnal birds of prey (eagles, hawks, kites and relatives – order Accipitriformes), but are in their own order Falconiformes on a different branch of the avian genetic tree, related instead to the parrots and the passerines or songbirds! Functionally they are still raptors, but only convergently resembling the hawks. There is a single family, Falconidae, within the order, divided into several subfamilies: Herpetotherinae (Laughing Falcon Herpetotheres and forest falcons Micrastur); Polyborinae (Spot-winged Falconet Spiziapteryx, caracaras Caracara and Daptrius); and Falconinae (pygmy falcons Polihierax and Neohierax, falconets Microhierax, falcons Falco). The first two subfamilies are South American, and the last is cosmopolitan, although the pygmy falcons and falconets are restricted to Africa (Polihierax) and Asia (Neohierax and Microhierax). Only Falco occurs in Australasia.

The order Falconiformes apparently originated in the South American part of Gondwana, where the greatest morphological and generic diversity of living members now lives – the caracaras, forest falcons, Laughing Falcon and Spiziapteryx as well as Falco. An early falconid fossil is known from Antarctica, which was the part of Gondwana joining South America to Australia. It was only during the geologically fairly recent global spread of grasslands that the genus of true falcons (Falco) arose in open environments and diversified rapidly. Having long, pointed wings for sustained flight and capable of ocean crossings, falcons were able to colonise the rest of the world. The process apparently started with an ancestor of the kestrels, in Africa, branching off from the ancestor of Neohierax of Asia. An earlier branch in the tree gave rise to Polihierax in Africa and Microhierax in Asia – these Old World pygmy falcons and falconets being tiny, shrike-like (passerine family Laniidae) proto-falcons.

On the whole, the falcons (genus Falco) are characterised by their bill structure (tomial ‘tooth’ on the upper mandible and corresponding notch in the lower mandible); pale or brightly coloured facial skin (cere, orbital rings); dark eyes; malar stripe (moustachial streak or ‘teardrop’ mark); wings lacking the ‘fingered’ tips (strongly emarginated primaries) of most soaring hawks; and the habit by perched individuals of head-bobbing when appraising an object of interest or alarm. The latest DNA research has identified several recognisable groups of falcons, and has somewhat reorganised the traditional view, and at the time rather radical (and now unsupported) HANZAB view, of Falco relationships. These groups are here enumerated in approximately ascending evolutionary sequence. For a diagram of the Falco genetic tree, see the supplementary material in the paper by Schoenjahn et al. (2020) under Grey Falcon in the Bibliography.

Old World kestrels near the base of the Falco genetic tree on their own branch: typified by the Eurasian Kestrel Falco tinnunculus and to which our Nankeen Kestrel belongs, along with the latter’s close relative, the Moluccan or Spotted Kestrel F. moluccensis of Indonesia and islands off western New Guinea. This group is most diverse in Africa, where the most basal members occur, including the Rock Kestrel F. rupicolus, which is now afforded specific rank basal to the aforementioned Eurasian-Australasian trio. All other falcons are on a separate branching of the tree, with the American Kestrel F. sparverius near the base of that branch (and thus convergently like the Old World kestrels). On the whole, the Old World kestrels can be characterised as small, hovering and perch-hunting, ground-pouncing generalists and insectivores with rufous dorsal tones, sexually dimorphic plumage and a black subterminal tail band. However, a basal member and early colonist of Madagascar (the Banded Kestrel F. zoniventris) has become a dark, heavily marked, forest inhabitant and reptile specialist, its plumage convergently resembling that of some endemic forest-dwelling members of the hawk family there (Madagascar Serpent-Eagle Eutriorchis and certain accipiters).

Merlins and relatives, clustering on three separate sub-branches: the Merlin Falco columbarius (actually two species – F. columbarius in North America and F. aesalon in Eurasia); the Red-footed and Amur Falcons F. vespertinus and F. amurensis (Eurasian migrants to Africa/Madagascar); and the Dickinson’s and Grey Kestrels F. dickinsoni and F. ardosiaceus of Africa. The merlins are classic, if small, aerial bird-chasing falcons, but the red-footed falcons are more like kestrels in habits, and the last two African species are indeed kestrel-like in habits. Overall, the group is characterised by grey dorsal plumage and, in some species (or the males of some), grey ventral plumage too. This group is not represented in Australasia.

The Australian Brown Falcon, sitting on its own branch basal to the next few groups. It is thus an early endemic, rather like a large, long-legged kestrel, without close extant relatives. It is a usually slow-flying, perch-hunting and sometimes hovering, ground-pouncing generalist that has some adaptations for catching venomous reptiles, such as ‘armoured’ legs (large, coarse scales on the tarsi), dense ventral plumage and the behavioural capacity to evade defensive strikes by snakes while capturing and subduing them. It is highly vocal, uttering loud squawks and crowing calls. In the absence of snake-eagles (Circaetus species) in Australia, it has extended into that niche. Historically considered an unusual or aberrant falcon perhaps deserving its own genus, on DNA evidence it clearly sits within Falco.

Hobbies: a group of small, fast, highly aerial falcons that chase birds, microbats and flying insects. Basal in the group are the Bat Falcon Falco rufigularis and Orange-breasted Falcon F. deiroleucus of South America, and basal in the Old World hobbies is our Australian Hobby. The other Old World hobbies cluster more closely with one another: the Oriental Hobby F. severus (Asia to Melanesia), Eleonora’s Falcon F. eleonorae and Sooty Falcon F. concolor (Mediterranean/Middle East, migrating to Madagascar), along with the Eurasian Hobby F. subbuteo and its possibly conspecific relative, the African Hobby F. cuvieri. The more typical members have a dark partial ‘helmet’ and malar stripe, grey dorsal plumage and at least some rufous in the ventral plumage.

What could be termed a trans-Pacific pair of falcons, on the next branch of the tree: the Aplomado Falcon Falco femoralis of Central and South America and, surprisingly, the New Zealand Falcon F. novaeseelandiae. Although now well separated by ocean and their ancestral dispersal routes unclear, a vague resemblance is apparent between the adult New Zealand Falcon and the juvenile Aplomado Falcon. In the absence of goshawks and sparrowhawks (Accipiter) in forested (or formerly forested) New Zealand, the endemic falcon there extends into that niche, with shorter and more rounded wing tips than most other falcons. In the absence of mammalian predators (until those introduced by European settlers), the New Zealand Falcon nests on the ground as well as on elevated sites. The Aplomado Falcon’s plumage resembles, perhaps convergently, that of the two South American hobbies (Bat Falcon and Orange-breasted Falcon), suggesting some common influence of habitat on plumage expression.

Adult Grey Falcon, Australia’s rarest and most threatened falcon and one of our special endemics. Photo: © Matt Wright/Faunagraphic.com.au

The hierofalcon/peregrine cluster, with the Red-headed Falcon Falco chicquera (Afro-Asia) basal on that branch, and the Prairie Falcon F. mexicanus (North America) and our Grey Falcon branching off earlier than the hierofalcon/peregrine split. The physical resemblance, other than the rusty cap, between the Red-headed Falcon (Indian subspecies) and plainer Grey Falcon is readily apparent. All are fast bird-chasers; the others in the group can be further characterised as follows.

Hierofalcons, otherwise known as ‘great falcons’ or ‘desert falcons’: the Lanner Falcon Falco biarmicus (basal on the branch – Africa/Mediterranean), Laggar Falcon F. jugger (India), Saker Falcon F. cherrug (Eurasia), Gyrfalcon F. rusticolus (Holarctic), and our Black Falcon, which is recently derived from Laggar Falcon stock and resembles a juvenile Laggar. They include the largest falcon (the Gyrfalcon), and are rather more generalised in foraging ecology than the peregrines, variously taking more mammals, reptiles and insects along with birds. Most are paler than the Peregrine Falcon, with a wispy malar stripe rather than a thick malar stripe or full ‘helmet’. The Lanner and Laggar have a rusty cap.

Peregrines: the Taita Falcon F. fasciinucha (a small African species, basal on this branch), Barbary Falcon F. pelegrinoides (North Africa/Middle East to western Asia) and cosmopolitan Peregrine Falcon F. peregrinus. The Peregrine Falcon appears to have originated in the Mediterranean region where its basal subspecies occurs, apparently having evolved to hunt a fast-flying pigeon – the cliff-dwelling wild Rock Dove, long domesticated as a racing or homing pigeon (among its other breeds) and now the feral pigeon of human landscapes. The Peregrine’s powers of flight have enabled it to occupy the globe (except Antarctica), although by the time it colonised South America a large and robust endemic hobby (the Orange-breasted Falcon) had already partly filled that niche, alongside the latter’s more typical hobby sister-species (the Bat Falcon). The Barbary Falcon, having a rusty cap like some hierofalcons, is a paler, desert-dwelling offshoot of the Peregrine Falcon, tending now to be treated as a separate species rather than as subspecies of the Peregrine.

The centre of diversity and endemism in Falco is Africa (including Madagascar), with 14 of the 40 currently recognised species occurring or centred there, and seven others wintering there from breeding populations in the Mediterranean/Middle East and Eurasia. All the major falcon groups are represented there; that is, Old World kestrels, merlin group, hobbies, hierofalcons and peregrines. In most cases, other than hobbies, the African representatives of these groups are basal on their respective branch of the Falco genetic tree.

The molecular clock determined by the Falco DNA and falconid fossil research places the ancestral Brown Falcon arising in or colonising Australia ~5 million years ago; the Australian Hobby and Grey Falcon ~2 million years ago; the Nankeen Kestrel less than a million years ago; the Black Falcon less than half a million years ago; and the Peregrine Falcon less than 300 000 years ago (consistent with the last having diversified only into a resident, endemic subspecies). This pattern suggests an independent origin and history for each of the six Australian falcons. However, given the estimated timing, it is likely that all six, or their ancestors, arrived in Australia via Asia. The timing of the Aplomado Falcon/New Zealand Falcon split also approximates that of the South American hobbies/Australian Hobby split (i.e. ~2 million years ago), suggesting a dispersal or colonisation event of two Falco lineages reaching South America and Australia/New Zealand at around the same time.

This book deals only with the six indigenous Australian falcons, although there are three others resident in the Australasian faunal region, which extends from Wallacea to Oceania and New Zealand (Table i.1). The Oriental Hobby could conceivably turn up on Cape York Peninsula, a short island-hop across Torres Strait from its range in New Guinea, and is possible on Dauan, Boigu and Saibai Islands (Australian territory hard up against New Guinea), but there is nothing to add to recent global raptor treatises on this poorly known species. The Eurasian Hobby is a rare overshooting migrant to the Australian territories of Christmas and Cocos (Keeling) Islands in the Indian Ocean, eclipsed in recent times by single individuals appearing near Perth in six consecutive summers and one found injured in East Gippsland (Victoria) – either overshooting or wrong-way migration. Their occurrence is biologically irrelevant to the Australian raptor community; the birdwatching excitement so generated might be better directed to understanding our Australian Hobby more fully (for comparison, there are whole monographs devoted to the Eurasian Hobby!). Without first-hand experience of the New Zealand Falcon it would be presumptuous to include it here; nevertheless, the substantial post-HANZAB studies are listed in the Bibliography, if only to flag what we still need to achieve on most of the Australian species. In any case, a monograph on the New Zealand Falcon (Bell 2022) has been published.

The Black-shouldered Kite Elanus axillaris is, genetically, a member of a genus basal in the hawk family tree (family Accipitridae, not close to the Falconidae). Notwithstanding the Kite’s falcon-like pointed wings and kestrel-like winnowing and hovering flight, DNA comparisons place the genus Elanus firmly with the hawks, as do aspects of the Kite’s anatomy. The elanine kites apparently originated in Gondwana, with Elanus almost cosmopolitan in warmer climes (two species endemic in Australia, one in the Old World, one in the Americas), one genus endemic in Africa (monotypic Chelictinia – much like a fork-tailed Elanus) and one genus (monotypic Gampsonyx –somewhat like a darker, more contrasting juvenile Elanus) endemic in South America. The second Australian Elanus species is the Letter-winged Kite E. scriptus, but being a nocturnal desert-dweller it is superficially more owl-like than falcon-like. The Black-winged Kite E. caeruleus of the Old World reaches the Australasian region, in Wallacea and New Guinea.

Table i.1. World falcon groups represented in Australasia (Wallacea to New Zealand), arranged phylogenetically according to the latest DNA evidence.

‘Endemic’ for the Grey Falcon and Black Falcon disregards unconfirmed reports of extralimital vagrants. Global conservation status (IUCN Red List and Action Plan for Australian Birds 2020): NT = near threatened; V = vulnerable; E = endangered.

aEssentially a regional endemic, except for (initially) probably ship-assisted vagrant(s) or colonists to Java and Christmas Island, respectively

bIts sister species being the Aplomado Falcon F. femoralis of Central and South America

cEndemic subspecies F. p. nesiotes in Fiji; F. p. macropus in Australia

Plan of this book

The book is organised in taxonomic sequence according to the above phylogenetic groups of falcons, i.e. (1) Old World kestrels; (2) Brown Falcon; (3) hobbies; (4) Grey Falcon; (5) hierofalcons (Black Falcon); and (6) Peregrine Falcon. A further section presents a photographic account of typical falcon breeding cycles, and a final chapter gives an account of a falcon-like hawk, the Black-shouldered Kite. The emphasis is largely on updating HANZAB (Marchant and Higgins 1993) with subsequent studies.

I stress that this book adds to, but is not intended to replace, HANZAB, so it should be read in conjunction with HANZAB. For ease of comparison, this book is similarly structured and formatted; the HANZAB headings and subheadings are generally followed, except where there is no new material to add under a particular topic. A footnote (‘Commentary’) explores additional aspects of ecology or behaviour.

As for this book’s predecessor (Australasian Eagles and Eagle-like Birds, 2017), the value and significance of recent findings are simply to provide an update of knowledge on the autecology of the individual species, as a basis for conservation and management, and neither is intended to be a treatise on or synthesis of general raptor ecology, as that has been done by Penny Olsen’s book (Olsen 1995). Nevertheless, I have tried to take account here of the more critical reviews of the eagle book while not departing too much from the style of its HANZAB model.

Referencing

In the Bibliography, any references cited in multiple individual species accounts, if not found in the journal references for that species, are listed under ‘Books’. In the species accounts (e.g. under ‘Food’), ‘NSW Bird Rep’ (as in HANZAB) refers to the annual bird reports published in Australian Birds (journal of the NSW Field Ornithologists Club) for the specified calendar year.

Because field identification of raptors is a perennial issue, rather than cite field guides under each species account, the pertinent raptor field guides are listed under ‘Books’ in the Bibliography. Those applying to Australian species are Czechura and Field (2007), Debus (2019) and Seaton et al. (2019), and those applying to relevant overseas species or subspecies that might occur in Australia or at least the Australasian region (e.g. Eurasian and Oriental Hobbies, palaearctic Peregrine subspecies) are Ferguson-Lees and Christie (2001, 2005).

As the present book was being finished, David Hollands’ new book Birds of Prey of Australia (Hollands 2021 – see ‘Books’ in the Bibliography) appeared. Where appropriate I have added reference to his new (post-HANZAB) material not mentioned in his earlier book (1984 and 2003 editions).

Photographs

BirdLife Australia policy strongly discourages bird photography at nests, as do global raptor experts, because of the risk of nest failure from disturbance to or betrayal of the nest. Nest photography has long been accomplished for all Australian raptors, most recently by David Hollands in his book (2021), so there is no further need for it just for the sake of close-up photos. I therefore stress that the Grey Falcon photos by Matt Wright in this book were taken distantly, with an 800-mm lens and 1.4 × converter in minimal time, while the birds appeared comfortable, and were not part of the unethical episode described in the Grey Falcon chapter herein.

Nankeen Kestrel Falco cenchroides

The Nankeen Kestrel was described and named by Nicholas Vigors and Thomas Horsfield in 1827, from specimens collected by George Caley in the Sydney region in 1803.

Despite its abundance the Kestrel is little studied, and there is surprisingly little to add to the HANZAB account in almost three decades. Much recent research has concentrated on diet, partly in concert with attempts to mitigate aircraft strike at airports, and there has been only one preliminary study of colour-marked birds. By contrast, kestrel species in Britain, Europe and North America have been studied exhaustively. Australian academics and graduate students wanting to study raptors, and needing large sample sizes, need look no further than the Nankeen Kestrel as a species well worthy of detailed comparison with its overseas counterparts.

John Pastorelli’s Honours thesis (Pastorelli 1984) was not cited by HANZAB on the Kestrel, so the essentials are included here.

Field identification

The Nankeen Kestrel is still sometimes confused with the palest Brown Falcons Falco berigora, even to the point of misidentified photos of perched individuals of one or the other in contemporary popular publications. The key distinguishing features in such circumstances are the Brown Falcon’s long grey legs, brown thigh feathers and lack of a black subterminal band on the tail, versus the Kestrel’s short yellow legs and lack of brown thigh feathers. In some light conditions, e.g. in brief views when only silhouetted, Kestrels can be confused with the Australian Hobby Falco longipennis, but are less dashing and rakish. The Kestrel can also be confused with the juvenile Black-shouldered Kite Elanus axillaris (see that account). Grey-capped male Kestrels, seen in flight from below (i.e. pale ventrally with their rufous upperparts not visible), can be optimistically mistaken for the Grey Falcon but are identified by their black subterminal tail band and hovering habit.

Pair of Nankeen Kestrels. Photo: © David Whelan/wildpix.com.au

Habitat

HANZAB characterised the Nankeen Kestrel’s habitat as ‘over open country and wooded lands, tropical and temperate … all altitudinal and rainfall zones … most common in open country with low, rather sparse vegetation … in well watered areas’, and listed typical tree, shrub and grass species. Post-1993 studies supplement HANZAB, with some additional specific detail particularly for the arid zone and tropics.

In central Australia, Kestrels were sighted in or over grassy Acacia shrubland, spinifex, low to tall grassy open woodland, grassland and bare ground; they nested in River Red Gum Eucalyptus camaldulensis riparian woodland (Aumann 2001b,c). In the Lake Eyre Basin, Kestrels occur in a variety of habitats present (riparian and other woodland, sand dunes, chenopod and other plains), but prefer gibber plains; they roost and nest in trees, cliffs, or buildings and other structures (e.g. abandoned railway sidings, large bridges) (Read and Badman 1999). In arid south-west Queensland, the Kestrel’s distribution coincides with the flatter and grassier habitats (alluvial floodouts, gibber, grasslands, sand dunes, river channels) rather than Acacia woodland on rocky hills (Ley et al. 2011). In Western Australia generally, the Kestrel inhabits treeless or sparsely wooded country, in deserts mainly around watercourses and rocky breakaways (Johnstone and Storr 1998). In the Pilbara (north-west WA), it prefers treeless or lightly wooded country, especially the coastal plain (Johnstone et al. 2013). In the southern Kimberley (northern WA), it favours the vicinity of riparian woodland, where it breeds in hollow River Red Gums (Coate et al. 1998). In the Top End (NT), it occurs in grassy floodplains and other open areas, woodland and cultivated areas, and also in urban areas around tall city buildings (Corbett et al. 2014; McCrie and Noske 2015). Kestrels forage over coastal cliffs, dunes and beaches, including urban sites (Burgess 2017; S. Debus), and they use artificial structures in rural, urban and industrial areas as hunting, feeding, loafing and roosting perches (Junckerstorff 1997; Williams 1997; Olsen 2014; Mo 2016; Burgess 2017; Lumnitzer 2017; S. Debus). In a farming district of southern Queensland, Kestrels were much more abundant in grain cropland than in cotton fields (Fitzsimmons 1997). On the lower north coast of New South Wales, Kestrels preferred natural grassland > 10 cm high (94% of sightings) over ‘improved’ grassland (< 70% cover, < 10 cm high, grazed/mown/burnt); for perches they used live trees (5% of sightings), dead trees and utility poles (79%), utility wires (12%) and fence posts (4%) (Pastorelli 1984). In the Riverina of New South Wales, Kestrels were more abundant on open grassy plains with scattered trees and chenopod shrubs than in sheep/wheat fields with remnant woodland or in irrigation areas with rice or sheep/wheat fields and horticultural plantings (Brickhill