<b>Have Asian Koels Evolved Egg Mimicry with Any of Their Hosts?</b>
<p dir="ltr">We took objective measurements of koel and host egg color, luminance, pattern and size using reflectance spectrophotometry, photographs and calipers using eggs from the collections of the Natural History Museum (NHM) in Tring, UK. The pattern and size of parasitized clut...
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2025
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| Summary: | <p dir="ltr">We took objective measurements of koel and host egg color, luminance, pattern and size using reflectance spectrophotometry, photographs and calipers using eggs from the collections of the Natural History Museum (NHM) in Tring, UK. The pattern and size of parasitized clutches were measured in 2015 and the color, luminance and size of some parasitized and unparasitized clutches were measured in 2019 (please see below sections for more detail on methods and equipment). All the NHM eggs were collected between 1867 and 1943 from Bangladesh, India, Pakistan, Sri Lanka, Myanmar, Thailand, Indonesia and China. The sizes of other eggs were measured from 2008-2017 at a field site at Jahangirnagar University, Dhaka, Bangladesh using digital calipers. We measured clutches for 11 different host species of three koel subspecies (<i>E. s. chinensis</i>, <i>E. s. malayana</i>, and <i>E. s. scolopaceus</i>) from multiple countries (Table 1; Table 2; Figure 1; Supplementary Material, Table S1). The color, luminance and size of unparasitized clutches were measured to increase our sample size of host eggs and to allow us to make comparisons between hosts and potential hosts that were never or only rarely parasitized in the collection. Unparasitized and parasitized clutches for a given species were combined in all analyses. For the main analyses, we only included species with at least five clutches (five eggs from different nests) measured (Table 2).</p><p dir="ltr">The Asian Koel is a generalist brood parasite that exploits a diverse array of host species across Asia. <a href="" target="_blank">A</a> previous study using avian visual modeling found no evidence that koels had evolved eggs that mimic the eggs of one of their oldest known hosts, the House Crow (<i>Corvus splendens</i>) or had host-specific egg types when parasitizing two other common hosts in Bangladesh. In this study, we used museum collections to compare eggs from three koel subspecies to a broader range of host species from multiple areas across Asia. Our goals were to: 1) determine if koel eggs differed in appearance based on the host species’ they parasitized and 2) determine if koel eggs appear similar to the eggs of any of the hosts we measured, which might suggest egg mimicry. We found no evidence that koels have evolved host-specific egg types (all koel eggs were similar in appearance to each other regardless of host nest) or that koels had evolved egg mimicry with House Crows. Rather, koel eggs were the most similar in color to the Red-billed Blue Magpie (<i>Urocissa erythrorynhca</i>) in all geographic regions and were more similar in pattern to the other parasitized crow hosts than to House Crows in the same geographic region. Thus, there is some evidence that koels may have evolved eggs that mimic the eggs of these other hosts, rather than the eggs of the House Crow, but further experimentation testing these hosts for egg rejection ability is warranted.</p> |
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