Island tameness: an altered cardiovascular stress response in Galápagos marine iguanas.

Island tameness is a widely documented phenomenon in which island species, particularly those that have evolved with no or few natural predators, show a greatly reduced behavioral response when faced with unfamiliar predators. This insufficient anti-predator response has led to widespread population declines among many island species exposed to novel predators, and has become a serious conservation problem. Despite its prevalence, the underlying physiology of island tameness is not known.

Diel changes in plasma melatonin and corticosterone concentrations in tropical Nazca boobies (Sula granti) in relation to moon phase and age.

We investigated the effects of moon phases and age on diel rhythms of plasma melatonin and corticosterone in free-living Nazca boobies (Sula granti) on the Galápagos Islands, Ecuador. Melatonin and corticosterone secretion are regulated by the circadian system and the two hormones play a role in the control of locomotor activity and foraging, which can be influenced by moon phases. These seabirds have a long life span and in many vertebrates circadian function deteriorates with age.

Correlation between plasma steroids and chick visits by nonbreeding adult Nazca boobies.

Nonbreeding adult Nazca boobies (Sula granti) often approach unattended chicks and perform parental and/or aggressive behaviors toward the chicks. Earlier descriptions of these encounters included sexual behaviors as well. We studied hormonal correlates of chick visits by such nonbreeding boobies during the breeding season.

Hormonal correlates of siblicide in Galápagos Nazca boobies.

Nazca boobies (Sula granti) show unconditional obligate siblicide immediately after hatching, reducing the typical two-egg clutch size to one. We studied body mass changes and levels of testosterone (T), corticosterone (CORT), and progesterone (P) for A-chicks (dominant, first hatched), B-chicks (subordinate, second hatched), and singletons, during the first 7 days after hatching, when siblicide normally occurs. Mass increase with age was higher for A-chicks than for singletons and B-chicks.