For Nazca boobies, a seabird that inhabits the Galapagos islands, there is no sympathy among siblings; these birds practice obligate siblicide in which the first hatched chick almost always kills the second. Following the rules of limited resources, it is advantageous to be an only child. In fact, the mother booby does nothing to stop the harsh behavior; she laid the second egg as a mere insurance policy and knows that she does not have enough energy to nurture both offspring.
Although in future years to come big brother may not be the only threat to booby populations. A new study from PLOS One shows that shrinking sardine numbers, the small fish which lives in the ocean around the Galapagos and provides food for the seabirds, will likely affect Nazca boobies. With the absence of sardines, the birds will replace the fish with a less nutritious diet.
The study showed that as flying fish replaced sardines in the birds' diet, "reproductive success was halved," said Emily Tompkins, lead author of the study. "If the current links between diet and reproduction persist in the future, and rising ocean temperatures exclude sardines from the Galápagos, we forecast the Nazca booby population will decline," Tompkins said.