Egg characteristics are unreliable in determining maternity in communal clutches of guira cuckoos Guira guira

Abstract

Egg characteristics have been used to determine egg maternity for birds in situations where two or more females lay eggs in a single nest (as in communal breeders and intraspecific parasites). We assessed the applicability of egg morphometry and eggshell appearance in ascribing egg ownership in communal clutches of guira cuckoos Guira guira, a species where up to seven females may lay eggs in a joint nest. We used both combined variables (including egg mass, length, width, shape and two eggshell variables), and a shape index to test whether eggs laid by each female were similar but different from eggs laid by other females. Also, we conducted discriminant function analyses to verify if eggs could be correctly classified to their mothers based on their characteristics. The correct maternity was determined by yolk protein electrophoresis of freshly‐laid eggs. Individual female chutches were separated through egg characteristics or shape alone in 29% and 41% of the groups tested, respectively. Differences were mostly due to a single female that differed from her nest‐mates in a unique egg variable. On average, 55% of the eggs analyzed were not assigned to the correct mother using egg dimensions and eggshell speckling pattern. In conclusion, the egg characteristics used do not reliably indicate maternity in guira cuckoo communal clutches. We therefore recommend a protein‐based verification of egg appearance characteristics for assigning maternity in other species in which multiple female laying occurs.

The importance of genetic evidence for identifying intra-specific brood parasitism

“…To summarize, we offer genetic evidence that a case of super‐normal clutch size in the northern lapwing did not involve IBP. Further, the absence of IBP in a nest with varying egg morphology supports the findings of other authors (McRae 1997, Ådahl et al 2004, Cariello et al 2004). These results suggest that classifying IBP based on egg characteristics is too tentative and that IBP should be genetically analysed.…”

“…We have not found other studies that have used molecular evidence to analyse if egg characteristics predicts intra‐specific brood parasitism (IBP) in shorebirds, but it has been done in the moorhen Gallinula chloropus (egg size, egg coloration, and interval between appearance of eggs; McRae 1997) and in the guira cuckoo Guira guira (egg size and colouration; Cariello et al 2004). These studies found that IBP could not be reliably determined based on egg size or egg colouration.…”

Natural History and Reproductive Biology of the Communally Breeding Greater Ani (Crotophaga major) at Gatún Lake, Panama

“…Three of the four species have been subjects of long-term behavioral studies: Groove-billed Ani (Crotophaga sulcirostris) in Costa Rica (Vehrencamp 1977(Vehrencamp , 1978Vehrencamp et al 1986;Koford et al 1990); Smooth-billed Ani (C. ani) in Florida and Puerto Rico (Davis 1940, Loflin 1983, Quinn and Startek-Foote 2000, Schmaltz et al 2008; and Guira Cuckoo (Guira guira) in Brazil (Macedo 1992;Cariello et al 2002Cariello et al , 2004Macedo et al 2004). Several individuals (both males and females) in all three species cooperate to build a single nest in which all of the females lay their eggs.…”

Variation in Size and Composition of Bufflehead (Bucephala Albeola) and Barrow's Goldeneye (Bucephala Islandica) Eggs

“…In addition to the Common Goldeneye, studies of the Ring-billed Gull (Larus delawarensis; Fetterolf and Blokpoel 1984) Cariello et al 2004), however, have found the opposite, that egg morphology is unreliable for the detection of nest parasitism. Therefore, evaluation of morphology-based methods appears to be necessary on a case-by-case basis for each species.…”