Comparative ecology of Pachyptila species breeding sympatrically at Gough Island

• Main Author: Jones, Christopher Warrick Price
• Other Authors: Ryan, Peter G
• Format: Master Thesis
• Language: English
• Published: University of Cape Town 2018
• Subjects: Zoology; Gough; Southern Ocean; Tristan
• Online Access: http://hdl.handle.net/11427/29646; https://open.uct.ac.za/bitstream/11427/29646/1/thesis_sci_2018_jones_christopher_warrick_price.pdf

Prions (Pachyptila spp.) are one of the most abundant seabird groups of the Southern Ocean but their taxonomy, at-sea distribution and foraging ecology are poorly known. There has been considerable confusion surrounding the taxonomy of prions and their identification at sea is problematic. Recent studies have confirmed the presence of two very similar prion species breeding sympatrically, approximately three months apart, on Gough Island: Pachyptila vittata and P. macgillivrayi. This discovery raised several questions about the ecological segregation of these species. My thesis compares the breeding distribution, at-sea movements, phenology, foraging ecology and trophic segregation of the two species at Gough Island, and compares Gough birds with the P. vittata from Tristan da Cunha. In 2000/01 it was estimated that 1.5–2.0 million pairs of prions bred on Gough Island, suggesting that this site supports the largest populations of both species in the world. However, the contribution of each species to this total as well as spatial and temporal segregation of the two species required further investigation. To investigate the breeding distribution and relative species proportions across Gough Island, 2227 prion specimens were collected opportunistically over several years at various sites. Most birds were caught at night or found dead, thus only provide an inference of breeding distribution. However, observations of incubating birds at several sites indicate that the data are representative of nesting distributions. At most sites there was evidence for consistent dominance of one or other species, although this need not mean local allopatry; a few P. vittata breed in Prion Cave, where P. macgillivrayi is by far the most abundant species. A few sites had both species in similar proportions, but these tended to be sites with relatively few birds and/or represent areas where the two species’ ranges abut. Weighting each site equally suggested a roughly equal ratio of P. vittata/P. macgillivrayi, but there was little ...