No evidence of host-specific egg mimicry in Asian koels

Abstract

Avian brood parasitism is costly for the host, in many cases leading to the evolution of defenses like discrimination of parasitic eggs. The parasite, in turn, may evolve mimetic eggs as a counter-adaptation to host egg rejection. Some generalist parasites have evolved host-specific races (gentes) that may mimic the eggs of their main hosts, while others have evolved ‘jack-of-all-trades’ egg phenotypes that mimic key features of the eggs of several different host species. The Asian koel (Eudynamys scolopaceus) is a widely distributed generalist brood parasite that exploits a wide range of host species. Based on human vision, previous studies have described Asian koel eggs as resembling those of its main host, the house crow (Corvus splendens). Using measurements of egg length and breadth, digital image analysis, reflectance spectrophotometry and avian visual modelling, we examined Asian koel egg variation and potential mimicry in egg size and shape, and eggshell pattern and color in three sympatrically occurring host species in Bangladesh: the common myna (Acridotheres tristis), house crow, and long-tailed shrike (Lanius schach). We found some differences among Asian koel eggs laid in different host nests: a) Asian koel eggs in long-tailed shrike nests were larger than those laid in common myna and house crow nests, and b) Asian koel eggs in house crow nests were less elongated than those in common myna nests. However, these changes in Asian koel egg volume and shape were in the opposite direction with respect to their corresponding host egg characteristics. Thus, our study found no evidence for Asian koel host-specific egg mimicry in three sympatrically occurring host species.

Asian koel rapidly locates host breeding in novel nest sites

“…The breeding season of the common myna lasts from March to August in Bangladesh but can in some areas continue throughout the whole year (Begum et al., 2011a ; Nahid et al., 2020 ). Common myna eggs are immaculate blue, and the clutch size is usually within 4–5 eggs (Nahid et al., 2021 ). The Oriental magpie robin ( Copsychus saularis ) and jungle myna ( Acridotheres fuscus ) are also common breeding birds within the study area, but there are no records in literature on Oriental magpie robin or jungle myna parasitism by the Asian koel (Erritzøe et al., 2012 ; Payne, 2005 ), nor any former records from the study area (Nahid unpublished data).…”

“…We monitored the nest boxes regularly (at least once a week) to acquire data on the nest building process by the common myna, and later to examine whether a clutch was parasitized by the Asian koel. Asian koel eggs were easily distinguished from common myna eggs by its color, pattern, and size (Nahid et al., 2021 ; Figure 2 ). Moreover, Oriental magpie robin and jungle myna eggs would also easily distinguishable from Asian koel egg (Begum et al., 2012 ; Karim & Ahsan, 2016 ; Nahid et al., 2021 ).…”

“…Asian koel eggs were easily distinguished from common myna eggs by its color, pattern, and size (Nahid et al., 2021 ; Figure 2 ). Moreover, Oriental magpie robin and jungle myna eggs would also easily distinguishable from Asian koel egg (Begum et al., 2012 ; Karim & Ahsan, 2016 ; Nahid et al., 2021 ). Nests that were predated and nests from fledged common myna clutches were regarded as empty nests without parental activity (i.e., inactive favorable nests; n = 83).…”

“…In our study area, the common myna ( Acridotheres tristis ) is a regular host of the Asian koel ( Eudynamys scolopaceus ), a non‐evictor, generalist brood parasite with general parasitism rates between 31.2% and 33.6% (Begum et al., 2011a , 2011b ; Nahid et al., 2021 ). The common myna usually builds different types of nests in cavities, including holes in trees, inside buildings or roofs, or in the small space between joining palm leaves of coconut ( Cocos nucifera ), fishtail palm ( Caryota urens ), and fountain palm ( Livistona chinensis ) trees.…”

“…The common myna usually builds different types of nests in cavities, including holes in trees, inside buildings or roofs, or in the small space between joining palm leaves of coconut ( Cocos nucifera ), fishtail palm ( Caryota urens ), and fountain palm ( Livistona chinensis ) trees. Occasionally common mynas utilize and repair old nests of pied mynas ( Gracupica contra ) or house crows ( Corvus splendens ) (Nahid et al., 2021 ). However, in our study area, the common myna is not familiar to nest boxes, and hence, nest boxes should constitute unfamiliar but attractive nest sites for common myna.…”