Oriental cuckoos (Cuculus optatus) vary the size of their eggs to match those of their hosts, a new study published in the Journal of Zoology has found.
Meshcheryagina et al find Oriental cuckoos (Cuculus optatus) change their egg sizes according to their host. Image credit: University of Hertfordshire.
Oriental cuckoos parasitize small warblers, whose nests are hard to reach as they nest high up in the tree canopy, this makes the study of their eggs more difficult.
University of Hertfordshire researcher Alla Mashanova and colleagues compared egg length, breadth and volume of Oriental cuckoo eggs with eggs of their four corresponding hosts: the Arctic warbler (Phylloscopus borealis), the common chiffchaff (P. collybita tristis), the yellow-browed warbler (P. inornatus) and Pallas’s leaf warbler (P. proregulus).
In addition to the field data, the team studied cuckoo and host eggs from oological collections.
“We found that the eggs’ breadth matched the hosts’ well, probably because a cuckoo’s egg sticking out above the rest of the clutch is likely to be rejected by the host,” Dr. Mashanova said.
“The egg length, on the other hand, was much more variable.”
A bigger egg containing more nutrients improves offspring quality, which is particularly important where only the female feeds the offspring, as is the case with Pallas’s leaf warbler.
“It has been suggested that the egg length is determined by the demand to produce eggs larger than the host’s and is affected by the level of parental care,” Dr. Mashanova said.
“Thus, the longest eggs were produced by cuckoos parasitizing the smallest host with only the female feeding the young.”
“In our view, differences in eggs sizes of the Oriental cuckoo provides evidence of adaptation to brood parasitism on small leaf warbler species.”
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S.G. Meshcheryagina et al. Host species determines egg size in Oriental cuckoo. Journal of Zoology, published online July 2, 2018; doi: 10.1111/jzo.12583
