Begging and provisioning of thin-billed prions, Pachyptila belcheri, are related to testosterone and corticosterone

Vigorous begging is usually seen as an expression of parent–offspring conflict over limited resources. Chicks signal need by begging, but the evolution of honest signals requires the signals to be costly. Although some possible costs have been identified, the cost-inducing mechanisms underlying this widely distributed signalling system remain unclear. Because hormones associated with stress and hunger (corticosterone) and aggressive behaviour (testosterone) have deleterious side-effects, signalling costs may be coupled to the expression of such hormones, if they are closely associated with the signal. We tested whether begging in chicks of thin-billed prions (Aves, Procellariiformes) is associated with secretion of corticosterone and testosterone. Prion chicks honestly signalled their nutritional state. Begging increased with decreased body condition, both within and between chicks. Adults responded to more intense begging by delivering larger meals. Chick testosterone levels were positively correlated with measures of begging intensity and the mean body condition of chicks was correlated positively with testosterone and negatively with corticosterone. In a cross-fostering experiment, the change in testosterone and corticosterone between control and experimental periods was positively correlated with the change in begging intensity. This is the first experimental evidence that the control of chick begging by endogenously produced testosterone and corticosterone may form a mechanism controlling parental provisioning in birds, and that chick behaviour can help to explain the variation in growth patterns between individual birds.

Niche separation in burrowing seabirds in Bass Strait

Islands in north-central Bass Strait support significant populations of short-tailed shearwaters, little penguins, fairy prions and common diving-petrels. Dietary analyses showed that while penguins consume mainly fish, the other species primarily feed on krill. Together, these seabirds consume an estimated 1,270,200 tonnes of prey throughout Bass Strait during breeding.

The significance of northern-central Bass Strait in south-eastern Australia as habitat for burrowing seabirds

The present study provides the first complete estimate of the abundance and distribution of burrowing seabirds in northern-central Bass Strait, a key region for breeding seabirds in south-eastern Australia. The estimated total number of breeding burrows in the region in 2008-11 were 755300±32400 (s.e.) burrows of Short-tailed Shearwaters (Ardenna tenuirostris), 26700±3500 of Little Penguins (Eudyptula minor), 19100±2200 of Common Diving-Petrels (Pelecanoides urinatrix) and 4200±2700 of Fairy Prions (Pachyptila turtur). These represent substantial proportions of the total estimated Australian breeding populations of these species: 6% of the total population of Short-tailed Shearwaters, 14% of Little Penguins, 0.4% of Fairy Prions and 13% of Common Diving-Petrels. Based on the number of active burrows, the number of breeding Short-tailed Shearwaters in the region is estimated to have decreased 35% between 1978-80 and 2008-11, equivalent to a decrease of 1.4% per annum between 1980 and 2011. The regional population of Little Penguins, however, appears to have increased substantially over the same period. Identification of population trends of the other species is limited by a lack of previous data. The importance of this area for burrowing seabirds and the substantial decline in numbers of Short-tailed Shearwaters warrants more frequent monitoring of the abundance of seabirds in the region to allow a robust comparison of changes in populations over time as well as the identification of possible causative factors. © BirdLife Australia 2014.