Raptors of mainland Eurasia
Our aim is to develop identification apps for the raptors occurring on the mainland of Eurasia. We see Europe as it is geographically - a western peninsula of Asia, and not the centre of the world, as it is often regarded. We have restricted us to the "mainland" mostly because we do not include the Sundaic archipelago and Philippines - we have too little personal experience of the birds there. But we do include Japan, Taiwan, Sri Lanka and even the British Isles. Very rare accidentals, such as African and northern American vagrants to Europe are not included, at least for now.
We aim to be practical. The identification characters mentioned have been regarded by us to be useful in at least some situations. We have made an effort to use terminology which is both consistent and as minimal as possible.
Raptors of mainland Eurasia. Accipiters, Harriers, Buteos, Honey-buzzards and Kites. Android app. ver 1.6.501 Published 30 December 2018. Download from Google Play, search for "Raptors Accipiter"
The next part will include Buteo buzzards.
Raptors, or diurnal birds of prey, as understood here, consist of two only distantly related groups, hawks, eagles and vultures (order Accipitriformes) and falcons (order Falconiformes). The common thing between them is their habit of preying on birds and small mammals, although many consume reptiles and larger insects too, and several are more or less specialised carrion eaters.
The aim of this work is to help identifying the raptors occurring on the mainland of Eurasia in the field. All regular and most vagrant species from the Atlantic to the Pacific coast and from the Arctic Sea to the Indian Ocean and the Mediterranean are included. All regular species of Japan, Taiwan, Sri Lanka and the British Isles are also included.
The aim is to present the species and subspecies identification, age and sex characters as concisely and simply as possible, but avoiding oversimplification. In some cases, even more detailed ageing and sexing is possible by experts, but we have considered them too complicated and the error margin too broad for them to be included in a general guide. Many species are well studied, especially those occurring in the western part of Palearctic. However, there are still several cases where we have not enough information for the topics of this guide, identification, moult and breeding, and further studies are essential. We have not tried to hide but highlight these cases.
Taxonomy used is chosen from the practical viewpoint and no single authority has been followed. The described taxa should be easy to understand in all modern taxonomical contexts. The most controversial taxonomic issues among the raptors of the region are those concerning smaller Buteo buzzards and Milvus kites. In subspecific taxonomy there are more widely problematic issues in Golden Eagle and Peregrine, and some other too. Not all generally accepted subspecies are described, some are considered too weakly defined for field identification, or even for identifying single individuals in the hand. In some cases we may be wrong, and those taxa really are identifiable - this remains to be seen.
Most of the information is of course not based on our own studies, but gathered by others during the centuries and decades of ornithology. Although we are very fond of literature references in general, we have not included them in the main text of this work, in order to make it as concise as possible, as is the common practice in identification guides. The literature section includes a long list of relevant works on the raptors of the region.
Photos are heavily edited in order to be easily comparable. They should be seen to be somewhere in between paintings made for field guide use and “real” photographs. For example, many of the photos are mirror images of the original. We chose to do that for visual reasons, although it may cause some minor irritation in cases where there are several images of the same individual. Apologies to some photographers for modifying their splendid works.
Distribution. Some important information about distribution is included, but only very shortly, to show approximately where the species can be expected and at what time of the year. More in-depth data could be found in other literature. Extralimital range has not been described.
Geographical variation. Subspecies that can be identified in practice are described. This means that many of those should be identifiable even out of their geographical context - for example, as a passage migrant or wintering birds where several subspecies occur together. In some cases, if the variation is both marked and complex, several subspecies are given their own chapters, and their distribution is then described under Distribution.
Life cycle. Information about the breeding period, which is essential in understanding the plumage development, but in very compressed form. Short information on adult moult cycle is included, because it is important in identification. The information about possibly differing moult before the definite cycle is in chapters First year or Subadult.
General. General information about the identification is given, like size, jizz and flight style.
Adult. Specific and ageing characters of adults.
First year. Ageing characters compared to adult, or subadult. Characters for separation from other species. These are given if appropriate - for example, it is possible that enough information for specific identification is already given in the General chapter.
Subadult. Ageing characters of identifiable subadult birds. Also, in some cases, information about specific identification.
Acknowledgements: We are most grateful to the staff and sponsors of The Natural History Museum, Tring and the Zoological Museum of the Moscow University, where we have been allowed to study raptor skins. We also thank the photographers, who have kindly provided photographs for this project, and Roy Hargreaves for reviewing the text. We are grateful to a number of people who have helped us and invited us to raptor watch with them in Asia, including Aki Aintila, Tom Beeke, Bob DeCandido, John Holmes, Paul Holt, Chukiat Nualsri, Martti Siponen and Tulsi Subedi. We are indebted to the late Visa Rauste, with whom we travelled widely and with whom we also enjoyed many long discussions about moult. Last but not least we also thank Dick Forsman for teaching us much about raptor identification and moult during the decades.
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Moult and plumage development
Understanding moult is very important for both species identification and, especially, ageing of the birds. One important thing to make it understandable is to choose the best descriptive terminology for moult and plumage development.
The term plumage has been used as a synonym for feather generation, for example by Humphrey & Parkes and the systems developed from it. The much more common use of the term differs from that and refers to feathers which the bird has at any given moment, or even how the feathers of the bird look without taking into account the moult at all (the term “plumage development”, for example refers to this latest concept). This is the plumage aspect in the terminology of Humphrey & Parkes. In practice, feather generation is not a very important term when describing looks of an individual bird or species, as typically done in identification guides. It is more apt when concentrating on moult, but in many raptor species the growth of one feather generation occurs during several, subsequent years and moult seasons, and the grade of maturation towards adult looks may differ accordingly within the same feather generation. Therefore the term plumage is reserved for more general and less technical use in this work.
The first feather generation of raptors grows when the young bird is still in the nest. It is called juvenile plumage. It is the only feather generation which grows simultaneously everywhere on the bird, and is ready in all feather tracts at about the same time. Therefore it is at first uniform and fresh, later more worn and bleached but still uniform. In some species, the first feathers are quite similar to the definite feathers of adult individuals (e.g. Microhierax), but in some other species, it is very differently coloured and patterned compared to the adult feathers (e.g. Nisaetus, Ichthyophaga).
In bird books, the age of a bird is often expressed with a term which refers to its plumage aspect, for example “first winter” or “adult”, or even “first winter plumage”. In this sense “plumage” clearly refers to the plumage aspect, but this kind of terminology easily becomes messy, if the bird plumage and moult is scrutinised more closely (and for example the bird is in its first winter, but the primaries are juvenile, and it may even have some third generation feathers later in the season and so on). Another terminology which describes the age of a bird refers to calendar years. The bird is in its first calender year (cy) during the year of its birth, 2cy from 1 January and so on. This terminology does not mix moult and age, but it is not very suitable for some subtropical and tropical birds including raptors, which may have have been born close to 1st January. In addition, in verbal descriptions, the change of the year changes the term also, although there is no change in the bird itself. There is also terminology referring to moult cycles (first cycle, second cycle etc, that is, whichever moult year is the current), but it is not very suitable for those raptors and other birds, which always have an incomplete annual moult. In addition, the onset of the new moult, the shedding of one small feather, changes the term, even when there are no readily visible differences in the bird and the bird next to it, which may look just the same, might be termed differently.
In this work, the first feather generation of bird is called first plumage or juvenile plumage - these two are interchangable. The “final” aspect of the bird, which will not change from year to year when the bird is matured enough, is called adult plumage. In fact, adult plumage may slowly change when the bird gets older but this change is not regular or great. In this, first plumage is a Humphrey-Parkesian term, but adult plumage is not - in their terminology it is adult plumage aspect, which in many species always consists of several feather generations. Otherwise, the term plumage is avoided as technical term, but is used sometimes as a general description like “plumage fresh” or “plumage variable” - referring to the plumage aspect. When describing single feathers or feather tracts, the term feather generation is used. When the feather generations are numbered from the birth of the bird, they may be abbreviated as 1g, 2g etc. The age of a bird is expressed in approximate years from the birth: the first year continues from the birth until about one year of age, the second year until when the individual is about two years old. If the bird is born in summer, a first year individual is first 1cy and then 2cy in calendar year terminology, a second year bird is 2cy/3cy respectively.
Juvenile - bird in the 1st plumage. Or feather, which is of the 1st generation = 1g feather.
Juvenile - type. A feather (never a bird) that looks at least superficially like a 1st generation feather, compared to an adult feather.
Adult - a bird in its definitive plumage. A plumage that does not mature any more, so does not change from year to year (at least not much, or regularly).
Immature - non-adult.
Subadult - non-adult and non-juvenile.
The following grouping is based on both moult strategy and plumage development. These are different things and should be understood separately, but contribute to the same (in our context, important) thing: development of the plumage aspect of the bird.
Group A. The first moult starts in the smallest species when the bird is a couple of months old, at the earliest. The first feathers to be seen moulted are on the mantle and scapulars, as well as the underparts and head (e.g. many Falco, Accipiter badius). New growing feathers are very similar to adult feathers and ageing is possible based on the difference in pattern and wear of the new and old feathers. The last feathers to change - at about one year of age - are wing and tail feathers and as they are the last to remain of the juvenile plumage, ageing must be based on them, which is often somewhat difficult. In this group, part of the body feathers are being moulted for the second time at the same time when the flight feathers are being moulted for the first time.
Group B. Some small species (for example, Accipiter nisus) do not moult at all before at about one year of age, with body feathers being moulted only slightly before the wing feather moult starts. The difference between groups A and B is not clear cut, and sometimes some individuals of the same species belong to group A and others to group B. In principle, the plumage aspect of birds in group B is adult when the first complete moult is finished, but in some species (for example, Accipiter gentilis) it is still somewhat less developed than the true mature adult plumage aspect.
Larger species are unable to moult all flight feathers during one moult period, that is: individual feathers are normally used for more than one year. In these species, the first moult starts when at about one year of age. Typically, also these species moult only for part of the year, but the moult is often suspended and resumed during the next moult period, and there may be several moult periods during the year (for example, summer and winter in migratory birds). Primaries are moulted from several places simultaneously so that the first moult wave starts during the first moult period, the second in the second or later moult period, when the first wave has reached, for example, the sixth innermost primary. Secondaries are also moulted in waves, but typically in more complicated sequences. Typically during the first and second moult periods smaller numbers of feathers are moulted than in later seasons - so immatures moult slower than adults. It takes several years to change all body feathers.
Group C. includes those species which have a moult cycle as described above and the second feather generation is adult-like or almost adult-like in appearance (for example, Spilornis cheela). In these species, first year birds are generally easy to recognise and also subadults are separable as long as they have juvenile flight feathers left (while the body plumage has moulted to adult-like aspect earlier).
Group D includes the species which moult like those in the group C, but the second feather generation is still distinctly immature compared to the feathers of full adult (e.g. Aquila chrysaetos, Aquila heliaca and all Haliaeetus). In these cases, typically, even the third generation feathers are still immature and the maturation does not advance by feather generation but by the year the feathers are grown (by the age of the bird). If body plumage and flight feathers differ distinctly in adults and juveniles, they typically mature at comparable speed. In practice, ageing is exact as long as there are juvenile flight feathers left and is still possible for some years after that, but more inexact and uncertain because of individual differences in plumage maturation and moult.
This guide goes somewhat beyond the basic level and some technical terminology is needed.
- Moult - regular change of bird feathers. It is annual in the species described here, with some additional moult during the first year of life in some birds.
- Moult suspension - In many individuals, the moult is started during the summer, suspended for the autumn migration and resumed after the wintering grounds are reached.
- Juvenile plumage - the first plumage of birds. Birds often have this plumage for about one year after hatching.
- First-year - bird during its first year of life.
- Adult - bird in which the plumage is fully matured, and therefore does not change in subsequent moults (at least regularly, or greatly).
- Subadult - bird which is post-juvenile, but still not in adult plumage.
- Flight feathers - wing and tail feathers. The largest feathers of the bird.
- Primaries - the outer, large feathers of birds, ten in Accipiter hawks. P1 is the innermost primary and P10 the outermost.The tip of P9 reaches between P5 and P6 means that the second outermost primary is longer than P5 but shorter than P6 in flight.
- Primary projection - the extent of the folded primaries on a perching bird,
- Secondaries - inner large wing feathers.
- Remiges - wing feathers.
- Rectrices - tail feathers.
- Fingers - the outermost primaries which for aerodynamical reasons are narrower towards the tip. Their tips are separate and protruding in flying birds.
- Wing coverts - the smaller feathers of the wing, anterior to the wing feathers.
- Mesial stripe - a longitudinal darkish stripe in the middle of the throat.
- Moustachial stripe - darkish stripe between throat and cheeks.
- Nuchal crest - a crest on the top of the head.
- Supercilium - a pale stripe from bill that reaches above the eye and towards the rear.
- Cere - an area of bare skin at the base of bill.
- Orbital ring - a ring of bare skin around the eye.