Thermal adaptation as a factor affecting colonizing success of introduced Sturnidae (Aves) in North America.

Abstract

Two species of starlings (Sturnidae) have established themselves in southwestern British Columbia: the crested myna (Sturnus cristatellus), by escape from captivity about 5897, and the common starling (Sturnus vulgaris), by natural invasion during the 1950's. The crested myna has shown little capacity to expand its range or its population. The common starling is in an active phase of increasing density and distribution. These sympatric populations have been studied over a period of 3 years. This paper reports comparative aspects of reproduction, and resource use by the two species.We have found that the nesting season for starlings was synchronized into definite peaks of nest building, egg laying, hatching and fledging, which was not the case for crested mynas.Clutch and brood sizes were higher in starlings than mynas. Starlings successfully reared more second broods than mynas (38% vs. 9%). Per 100 pairs/annum, starlings contributed significantly more offspring (547 compared to 238) to the sturnid population.Although development of plumage and endothermy were similar in myna and starling chicks, feeding rates, quality of foods, and subsequent growth rates of chicks were significantly different.Egg transplant and heater nest box experiments suggested that poor nest attentiveness and low incubation temperatures maintained by crested mynas resulted in the low hatching and consequent low fledging success.