Raptor Field ID tips

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11 years 9 months ago #631 by Doug
Doug created the topic: Raptor Field ID tips
HI All.

This is very much going to be a work in progress and as a result, any of you that have information and wish to contribute should feel free to do so. As I progress inmy attempts to learn more about bird, and specifically raptor biology, I will post more information and add whatever you all contrinute to this article.

General Biology and Evolution

This can be a useful aspect to raptor identification. An understanding of the development of this group of birds over thousands and millions of years can assist in understanding the group and the specific bird you are looking at.

There are a few aspects one can consider.

Hunting style of birds of prey has developed over miliions of years from the early insect eating birds of prey to the modern bird hunting raptors such as Falcons and Kestrels. Over all the hunting techniques and physique of the bird will differ depending on whether it has adapted to fast and acrobatic bird catching or slower insect gathering hunting techniques.

Physiology and it role in evolution can be evident in the specialisation of certain birds. As raptors have evolved, some of the specialised natures of the birds physiology can be outwardly visible. These may include bills e.g the toothed bill of the Faloniformes, changes in the legs e.g. the "double-jointed" knee of the African Harrier Hawk developed to get birds out of the nest and finally the "booted eagles". What the "Booting" means is that the scales on the lower legs are very indistinct and have almost dissapeared. This gives the effect when looking at the legs, that the entire foot and lower leg is almost wearing a smooth "boot".

Once you understand sopme of these differences, it helps to understand the family you are looking at.

Physiology

There are several aspects to the birds of prey that differ from family to family and this can help decide what family a bird belongs to.

The eyes of most birds of prey have been developed to give the birds excellent abillities see great distances. The eyes are thus very eliptical in shape instead of round and are not able to move very much in their sockets. For this reason, most birds of prey look around by swiveling their heads.

Legs and feet also have undergone various adaptations from the longer middle toe on some raptors to the almost complete lack of scales on the legs givinig the bird a "booted" appearance. Also of note is the difference in the hind toe between Old World and New World Vultures. In New World Vultures, the hind toe is small, non-functional and higher up the "foot" than the Old World birds.

Also the bills have undergone some adaptations like the heavy bills of Eagle for breaking up larger prey too the small "Toothed" bills of Falcons and Kestrels. In fact the toothed bill is pretty much exclusive to the Falconiformes.

As for size difference between male and female, the females in most raptors tend to be much larger than the males. This seems to be due to the fact that due to agressive predatory nature of raptors, the first thing a male would possibly do when seeing a female is to evaluate her as potential prey. This would affect breeding and paring so as a result it seems that with the female being up to twice the size of the male, this prevents the male from being able to attack a potential mate as prey.

Plumage and moult

Here are some rather interesting facts about these birds that can assist with ID.

Firstly, in the smaller birds (falcons, kestrels, sparrowhawks etc) up to the medium sized birds, a general rule is "Juveniles are Striped, Adults are barred".

Secondly, smaller birds take about 12 - 15 months to go from Juvenile to Adult PLumage. In the larger birds that take longer to mature, this can take up to 5 years and thus there are at least 5 if not more phases of variation between full juvenile and full adult plumage.

Also as a rule, back, tail and wing feathers tend to be tipped or emarginated buff-brown or dirty-white and dark areas tend to be duller and browner than in the adult plumages.

Juvenile feathers are longer than adult feathers (2 - 3 mm on the back and wings) and up to 7 cm (yes cm) in the tail, particularly in short-tailed birds. Bateleur can actually not have its short-tailed appearance in first year birds. The overall slightly longer feathers and obviously longer tail can affect giss of younger birds.

Moulting is also different. Small birds moult from the 10th primary in sequence. Larger birds can't afford to have adjacent feather missing as it can affect flight thus they moult from up to 4 different places in the wing at once. Also the moult can take several years in larger birds and thus you can have 1, 2 and 3 year old feathers in the wing at the same time.
Even mating birds moult at different times to non-mating birds due to food requirements of the pair rather than the individual bird.


Although this is a summary of only a few of the interesting points I have learned while researching raptors, I can strongly recommend getting the book listed in the references below. The information is detailed, comprehensive and if bird biology and its role in identification and the way the birds live, interests you then this book is a gold mine of information with about 135 pages in the begining of the book just covering biology of this group of birds from Evolution to physiology to Plumage to Wing-Loading and flight and even feeding and mortality of various species and those are just some of the 20 chapters of technical information.

References
Hawks, Eagles and Falcons of the world by Leslie Brown and Dean Amadon.

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