Cattle egrets, "Bubulcus ibis", exhibit asynchronous hatching and androgen loading in the first two eggs of their normal three-egg clutch. This results in older chicks being more aggressive and having a developmental head start. If food is scarce the third chick often dies or is killed by the larger siblings and so parental effort is distributed between the remaining chicks, which are hence more likely to survive to reproduce. The extra "excess" egg is possibly laid either due to exploit the possibility of elevated food abundance (as seen in the blue-footed booby, "Sula nebouxii") or due to the chance of sterility in one egg. This is suggested by studies into the common grackle, "Quiscalus quiscula" and the masked booby, "Sula dactylatra".