Comparison of kestrel skins and species

A phenotypic analysis of kestrel evolution by Boyce and White (1983) proposes that kestrels evolved out of Africa with the Fox Kestrel (F. alopex) as the ancestral stock. It is proposed that F. alopex subsequently occupied the holarctic but were driven south again during the glaciation events during the late Pliocene and Pleistocene. During this period, several species evolved (eg. F. moluccensis, F. cenchriodes, F. araea) but the Common Kestrel (F. tinnunculus) supposedly only moved south later.

Based on plumage differences, the Rock Kestrel in southern Africa differs markedly from the other subspecies of F. tinnunculus complex (Clarke 1995). Futhermore, females have typical male characteristics such as a grey head and tail and spotted rather than barred upperparts. Morphometrically, they are in a similar range as the other Common Kestrel subspecies (unpubl. data) but also fall within measurements of other species such as F. cenchroides. Rock Kestrels also inhabit mainly arid areas in Southern Africa, unlike their F. t. tinnunculus counterparts (Van Zyl 1997). Read Clark and Davies regarding their opinion of the status of the Rock and Mountain Kestrels. Information on how to tell the difference between F.t. tinnunculus, F.t. rufescens and F.t. rupicolus is outlined on a separate page written by Anthony van Zyl.

A previous study using DNA analysis (Seibold 1994) has shown that the Rock Kestrel cannot be classified as a separate species from the F. tinnunculus complex. However, this study analyzed limited material (only two samples from South Africa and one sample from Canary Islands) and only three subspecies. In a genetic analysis of kestrel species by Groombridge et al. (2002), the genetic differences of Common Kestrel subspecies from Europe (F. t. tinnunculus), the Canary Islands (F. t. canariensis and F. t. dacotiae) South Africa (F. t. rupicolus) and Kenya (F. t. rufescens) were analyzed. In this study, the Rock Kestrel from South Africa (F. t. rupicolus) plotted further from Common Kestrel F. t. tinnunculus than Australian Kestrel F. cenchroides, suggesting that it is genetically distinct at the species level.

The aims of this investigation to were to make some general notes on kestrel morphology only possible with comparable material and to specifically research the distribution and plumage differences in the skins of the kestrel species complex.  The relationship of the Amur Falcon (F. amurensis) and Redfooted Falcon (F. vespertinus) is discussed on a separate page.

Six hours were spent at the Natural History Museum in Tring, UK looking at the skins. Trays of skins were examined in the effort to sex and age the individuals and evaluate differences between species and subspecies. Sample male, female and occassionally immature specimens were selected to take reference photographs. Notes were taken on distribution of the subspecies of the Common Kestrels, especially on the edge of their ranges or where subspecies may overlap.

Interesting observations

The island kestrels - the smallest kestrels
There was a distince difference in the size of the island kestrels (Seychelles Kestrel, Mauritius Kestrel) compared to the mainland kestrels. However, the American Kestrel is found throughout the mainlands of North and South America but can also be classed as a small kestrel. Within the subspecies of the Common Kestrel, those subspecies on islands are smaller than those on the mainland, and those near the equator are smaller than those at higher latitudes.

Male, female and immature specimens of the smallest island kestrel, the Seychelles Kestrel Falco araea

Click on the pictures to see a larger image [Picture taken at the Natural History Museum, Tring, UK.]

Madagascar Kestrel - different morphs
The Madagascar Kestrel has two morphs, a light and dark morph. If the number of skins in the trays represent the proportions in the wild, it appears that the dark morph is not as common as the light morph. It is also interesting to note that the dark morph of the Madagascar Kestrel has a similar redish-brown spotted plumage to Rock Kestrel in Southern Africa.

Male specimens in light and dark morphs of the Madagascar Kestrel Falco newtoni

Click on the pictures to see a larger image [Picture taken at the Natural History Museum, Tring, UK.]

A comparison of plumage colouration of male specimens of Madagascar (Falco newtoni) on the left and Rock Kestrel (Falco t. rupicolus) on the right

Click on the pictures to see a larger image [Picture taken at the Natural History Museum, Tring, UK.]

Biggest vs Smallest
The biggest kestrel species, the Fox Kestrel (Falco alopex) is approximately three times the size of the smallest species, the Seychelles Kestrel (Falco araea).

Beaks of the grey kestrels
The grey kestrels have surprisingly heavy beaks compared to the other kestrel species. In particular, the aberrant Barred Kestrel (Falco zoniventris) from the forests of Madagascar has a particular heavy beak.

Subspecies of the Common Kestrel (Falco tinnnunculus) complex
There are nine or ten subspecies of the Common Kestrel. The nominate subspecies is F. tinnunculus tinnunculus is found from the western Europe and the United Kingdom, throught Europe, Asia, India, the Arabian Peninsula and Africa south to Tanzania and Angola. The other subspecies are:

• F. t. rupicolaeformis - Egypt and Arabian Peninsula
• F. t. rufescens (carlo) - Africa south of the Sahara extending south to Tanzania and northern Angola
• F. t. archeri - Somaliland and eastern Kenya
• F. t. rupicolus - southern Africa north into Angola, Zimbabwe and Malawi
• F. t. objurgatus - India and Ceylon
• F. t. interstinctus - eastern Asia
• F. t. neglectus - Cape Verde Island
• F. t. alexandri - Cape Verde Island - defined as own species by Browne 1955
• F. t. canariensis - Madeira Island, Canary Islands

Male specimens of the subspecies of Falco tinnununculus

Click on the pictures to see a larger image [Picture taken at the Natural History Museum, Tring, UK.]

Female specimens of the subspecies of Falco tinnununculus

Click on the pictures to see a larger image [Picture taken at the Natural History Museum, Tring, UK.]

Note how Falco tinnunuculus rupicolus stands out in both the male and female pictures.

Acknowledgments

I would like to thank the Natural History Museum, UK for access to the skin collection, and especially to Mark Adams for his help in the collection.

Boyce, D.A. & White, C.W. 1987. Evolutionary aspects of kestrel systematics: a scenario. In: The Ancestral Kestrel. Bird, D.M. & Bowman, R. (eds), pp. 1-21. Raptor Research Reports 6, McGill Univ., Quebec.
Clark, W.S. 1995. Some reflections on South African raptors by a North American visitor. Talon Talk 5:1.
Groombridge, J.J. et al. 2002. A molecular phylogeny of African kestrels with reference to divergence across the Indian Ocean. Molecular Phylogenetics and Evolution 25: 267–277.
Seibold, I. 1994. Untersuchungen zur molekularen Phylogenie der Greifvogel anhand von DNA-Sequenzen des mitochonriellen Cytochrom-b-Gens. Unpublished PHD thesis, Univ. of Heidelberg.
Van Zyl, A.J. 1997. Rock Kestrel Falco tinnunculus. In: The atlas of southern African birds. Vol. 1: Non-passerines. Harrison, J.A., Allan, D.G., Underhill, L.G., Herremans, M., Tree, A.J., Parker, V. & Brown, C.J. (eds), pp. 264-265. BirdLife South Africa, Johannesburg.