The recent expansion of an avian invasive species (the Cattle Egret Ardea ibis) in Algeria

This study identifies new information on the recent distribution of an invasive bird species, the Cattle Egret Ardea ibis, in Algeria. Breeding and wintering distributions as well as breeding numbers were obtained from large-scale surveys in 1999 and 2007, and from historical data. Between 1999 and 2007, the total number of colonies found increased from 51 to 87, and most were located in the northern part of the country. The breeding distribution area, confined to the coastal areas in the 1970s, has shifted further south, and reached the northern part of the Sahara since the 2000s. Most colonies were established during the period 1980–1995. The oldest colonies were generally larger than the recent ones. The number of colonies increased by 83% between 1999 and 2007 in the 12 administrative units (wilayas) surveyed. The number of breeding pairs increased from 7765 in 1999 to 28544 in 2007, corresponding to an annual population growth rate of 17.7%. The changes in distribution and population dynamics since the 1970s and the potential factors affecting these changes are discussed. ► In Algeria, the Cattle Egret expanded its range 560 km to the south in 40 years. ► Few hundred pairs were observed in the 70s; 87 colonies hosted 30 000 pairs in 2007. ► Agriculture fostered this expansion and the numerical increase in breeding numbers. ► The clutch size and realization of two broods per year also played a role.