Data from: Costly conspicuousness reveals benefits of sexual dimorphism in brood parasitic diederik cuckoos

The existence of adult sexual dimorphism is typically explained as a
consequence of sexual selection, yet coevolutionary drivers of sexual
dimorphism frequently remain untested. Here, I investigate the role of
sexual dimorphism in host-parasite interactions of the brood parasitic
diederik cuckoo, Chrysococcyx caprius. Female diederik cuckoos are more
cryptic in appearance and pose a threat to the clutch, while male diederik
cuckoos are conspicuous and not a direct threat. Specifically, I examine
whether sexual dimorphism in diederik cuckoos provokes threat-level
sensitive responses in Southern red bishop, Euplectes orix, hosts. I use
experimentally simulated nest intrusions to test whether hosts have the
capacity to differentially (i) detect, and/or (ii) discriminate between,
male and female diederik cuckoos, relative to harmless controls. Overall,
I found no evidence that diederik cuckoos differ in detectability, since
both sexes are comparable to controls in the probability and speed of host
detection. Furthermore, neither male nor female hosts discriminate between
sexually dimorphic diederik cuckoos when engaging in frontline nest
defences. However, hosts that witnessed a male diederik cuckoo during the
trial were more likely to reject odd eggs. Moreover, experimental eggs
were significantly more likely to be rejected when female bishops observed
a male compared to a female diederik cuckoo. While the cryptic appearance
of female diederik cuckoos does not reduce detection by hosts, it does
provide the benefit of anonymity given the egg rejection costs of
conspicuous male-like appearance in the nest vicinity. These findings have
implications for the evolution and maintenance of sexual dimorphism across
the Cuculidae, and highlight the value of testing assumptions about the
ecological drivers of sexual dimorphism.