WHAT IS THE REASON OF THE GREAT VARIATION IN CUCKOOS' EGGS?[1]
By Dr. E. Rey, Leipzig.
Translated and communicated by W. Wells Bladen, Vice-President, North Staffordshire Field Club.
Among the many attempted explanations of the great variation to be found in the colouring and markings of Cuckoos' eggs, the application of the Darwinian theory of selection seems at first sight to be most feasible. But on closer examination it does not appear to be in accordance with many well-founded facts. This theory supposes that those female Cuckoos whose eggs most resemble those of the nest chosen, have greater chance for the preservation of their offspring than others, whose eggs would be more liable to be destroyed by the foster-parents. As it may moreover be presumed that their daughters would lay eggs similarly coloured, and would make the same selection of nests for their offspring as their mothers, the consequence would be a preponderance of females whose eggs are similar to the nest eggs in colouring, whereas the other class would become more rare, and finally disappear.
I have already demonstrated in my work on the Cuckoo, and am now able to confirm by material at my disposal, and by nearly 2000 examples, that eggs matching those of the foster-parents are only to be found in a small percentage of cases. Those who only take into consideration the few examples in which Cuckoos' eggs are coloured like the nest-eggs, would alone venture to ask that the theory of selection should be accepted; whereas others, who consider the question in its entirety, will reject it as untenable, as far as the Cuckoo is concerned.
If the resemblance of its eggs to those of the foster-parents were such an advantage to the Cuckoo it would not be found as an exception to the rule, but would, on the contrary—at least here in the neighbourhood of Leipzig—be very perceptible in connection with Lanius collurio, most Cuckoos' eggs (84 per cent.) being found in the nests of these birds; of 282 Cuckoos' eggs found in the nests of the Red-backed Shrike, only sixteen, about 5 per cent, were of the type of Lanius eggs.
- ↑ "Was ist der Grund fur die grosse Variabilität der Kuckuckseier?" Ornith. Monatschrifte des deutschen Vereins z. Schutze der Vogelwelt. Jahrgang 1895. Nr 1.
