|The Collared Dove, Streptopelia decaocto|
The story of the colonisation of Europe by the Collared Dove (Streptopelia decaocto) is a truly remarable one. The bird was restricted to South Asia in prehistoric times, from where it spread to north China and the Middle East, partly with human help. It had spread to Syria and Turkey by the 16th century and had reached the borders of Europe by 1900 (1). Colonisation of Europe initially progressed along three routes; along the Adriatic into nothern Italy, northeastwards into Hungry and northweastwards through Central Europe (2). The first two of these routes were aborted, with colonisation into Central Europe continuting northwestardly until it reached the North Sea. Colonisation continued sideways and continues to do so today (3). It has been calculated that the expansion velocity of this colonisation is 43.7 km per year (1). A now common sight in many Irish gardens where it will often come to food, S. decaocto was unknown in this country until 1958 (4).
|Expansion of the Collared Dove (Streptopelia decaocto) in Europe from 1900 to 1970 (after Hengeveld, 1988)|
S. decaocto have a very long reproductive period, lasting from May til October. Female sexual maturity sets in after four months, so individuals born at the start of the reproductive season can breed by the end of it (1). While this goes some way to explain the speed of colonisation, it also begs the question why did it take until the 20th century to happen? A variety of reasons have been put forward, none of which are currently fully accepted. Change in nesting habits from using building to using trees may have opened new niches for the bird to exploit, fueling expansion (5). However it has been shown that S. decaocto nests in trees in other areas of its distribution, somewhat pouring cold water over this hypothesis. Climate change at the start of the 20th century resulting in milder winters and greater rainfall in the European continent may have given the bird the impetus to cross the barrier that the northern Balkans posed, opening the door to European colonisation (5). Changes in agricultural practices in Europe in the 20th century has also been suggested as a reason for expansion (5). This supplied S. decaocto with far more overwintering sites where food isn't a limiting factor. While all these hypothesies are valid, it is quite likely that a combination of these and other, as yet unforeseen factors facilitated the spread of S. decaocto.
- Hengeveld and van der Bosch, 1991. Ardea 79 pp. 67-72
- Hengeveld, 1988. Journal of Biogeography 15 pp. 819-828.
- Hengeveld, 1989. Dynamics of Biological Invasions pp. 92-115
- Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 70
- Rocha-Camarero and de Trucios, 2002. Bird Study 491 pp. 11-16