Focus on the Seychelles Turtle Dove (Streptopelia picturata rostrata/picturata)

A lot has been written about the Seychelles turtle dove (S. p. rostrata) and its progressive demise by cross-breeding with the larger and introduced Madagascar turtle dove (S. p. picturata). Although there is no real consensus the general view is that Madagascar turtle dove was introduced probably as a released food supply by a calling vessel in the mid-19th century - though Beamish (1981) states that it was introduced as recently as the early 20th century.

The Madagascan race is larger than the endemic Seychelles race and males compete for access to mates. The males face off side to side and jump and bat their near wing on the ground in aggressive displays. Feathers puffed out, back arched and outer wing raised they attempt to intimidate their opponent by the impression of greater size. If this does not work, then fighting can ensue with the birds then hitting each other rather than the ground with their wings until supremacy is established. The advantage is clearly with the larger bird resulting in more successful breeding by the Madagascan males and the spread of their physical characteristics through the population.

Some authors go into great detail describing fine differences between the phenotype of the two races for the purposes of this post however; Penny’s (1974) description will suffice:

“ Rostrata has a vinous red head, a chestnut mantle, grey brown under tail feathers and is much smaller”

“Picturata has a grey head, purplish mantle, white under tail and is larger”

For many years it was reported that individuals exhibiting the rostrata phenotype were restricted to the small islands of Aride, Cousin and Cousine. Penny (1974) also cites Fregate which makes sense as though not small it is the most isolated of the granitic islands.

Whilst working on Cousine Island in the mid-nineties I undertook a survey of the turtle dove population on the island. I caught, if I recall correctly, some 120 birds and scored them on various characteristics from plumage colour on various parts of their bodies, eye colour and various biometrics including wing length. Each bird measured was ringed to avoid repetition. At the time my results suggested that 1 in 3 turtle doves on the island still exhibited strong rostrata characteristics. I still have all the data in an old logbook at home one of several topics that fit into the likely doomed “I must write it up someday category…”

In 1995 Chris Feare – yes the same Chris Feare who is now working with us on the Sooty tern project – published a brief paper on his findings of turtle doves on Bird Island. Where, though admittedly with a small sample, his capture and grading of the birds suggested a population very close to the rostrata phenotype. Feare goes on to suggest that a small number of birds were either introduced or colonised naturally in the latter half of the 19th century and had persisted there largely unnoticed until changes in vegetation in the latter part of the 20th century allowed the population to increase.

Although not mentioned in the literature (indeed Hill 2002 states that the birds on Denis are of the picturata form) I have found there is definitely considerable variation in the physical characteristics of the doves on Denis (see photos in sidebar) and though I have not gone to the lengths of capturing and scoring the birds physical traits (too many more important and pressing issues to address) I think the population on Denis may be of interest in that regard.

This is notable because if the population on Denis were scored for its phenotype and then managed over a period of years it may be possible to bring back the endemic rostrata phenotype throughout the population. This due to Denis’ relative isolation could be maintained with just periodic monitoring and management.

A project for the future perhaps…

Refs:
Beamish, T. (1981). Birds of Seychelles. Dept of Agriculture. GoS.
Feare, C, J. & E.L. Gill (1995). The turtle doves of Bird Island, Seychelles. Bull. B.O.C. 1995 115(4).
Hill, M.J. Ed (2002). Biodiversity surveys and conservation potential of inner Seychelles islands. Atoll Research Bulletin. July 2002.
Penny, M. (1974). The birds of Seychelles and the Outlying islands. Collins. ISBN 0 00 219829 0