Potential nest selection factors and reproductive impacts of brood parasitic Asian Koel (Eudynamys scolopaceus) on host Long-tailed Shrike (Lanius schach) in central Thailand

Abstract

Avian brood parasitism can have severely detrimental effects on a host’s reproductive success and cause population declines. The Long-tailed Shrike (Lanius schach) is one of many hosts of the parasitic Asian Koel (Eudynamys scolopaceus). The Long-tailed Shrike subspecies longicaudatus, endemic to Thailand, is declining: however, the cause is unclear. The aims of this study are to (1) explore factors that influence the probability of Asian Koel parasitism on Long-tailed Shrikes; and (2) investigate the impact of parasitism on shrike reproductive success and whether it can account for part of this subspecies’ decline. Long-tailed Shrike nests were located and monitored for nest outcome throughout Sukhothai province in central Thailand. Habitat plots and point counts were conducted at the nest-sites to collect variables that had the potential to influence the probability of parasitism. Thirty-five active nests were located and there was a 68.6% parasitism rate. There was not a significant difference in either the nest success or the daily nest survival probability between parasitized and unparasitized nests—although the sample size was small. Crown diameter was the only variable that influenced the probability of parasitism—in which the larger the crown diameter, the lower the likelihood of parasitism. Our findings support previous studies which attribute foliage concealment (in this study quantified as crown diameter) to lowered parasitism rates.