Ecology, breeding biology and conservation status of the South Georgian Diving Petrels (Pelecanoides georgicus) on Codfish Island (Whenua Hou), New Zealand
Johannes H. Fischer, School of Biological Sciences, Victoria University of Wellington
The South Georgian Diving Petrel (Pelecanoides georgicus;SGDP hereafter) is a burrow-breeding Procellariiformes with a circumpolar distribution across the southern oceans and is currently considered “Least Concern” by the IUCN. In New Zealand, however, the SGDP has declined steeply due to a combination of predation by introduced species and habitat destruction. Subsequently the species became extinct on the South Island, Stewart Island, Auckland Islands and Chatham Islands. The only remaining New Zealand breeding population persists in the dunes of the Sealers Bay, Codfish Island (Whenua Hou), with a population size of 150 adults at most. Therefore, the species is considered “Threatened - Nationally Critical” by the New Zealand Threat Classification System. As this highly-threatened population is the only New Zealand Procellariiformes that specializes in breeding in coastal dunes, the Coastal Restoration Trust of New Zealand supported my research project aimed at better understanding the threats and population trends of the SGDP on Codfish Island. The proposed aims of this study were:
- Continued assessment of nest site characteristics critical to the SGDP on Codfish Island
- Assessment of population dynamics and trends of the SGDP on Codfish Island
- Assessment of the breeding biology of the SGDP on Codfish Island
Analysis of explanatory variables that potentially affect nest site selection in SGDPs on Codfish Island using a theoretic information criterion (AICC) showed that their nesting habitat are mobile, steep, north-eastern (seaward) facing dunes no further than 20 m from the sea. In addition, the interactions between the distance to the sea and physical aspects of the dunes, as well as the interaction between plant cover and the physical aspects of the dunes proved important. Surprisingly nest site selection by SGDPs is not dictated by the presence of invasive plant species (as opposed to the indications given by preliminary results), nor by the presence of conspecifics, Common Diving Petrels (P. urinatrix; CDP), or Sooty Shearwaters (Puffinus griseus). However, four burrows showing changes in occupancy suggest that CDPs may directly compete for burrow sites with SGDPs. More importantly, the preferred nesting habitat thus renders this Nationally Critical species extremely vulnerable to effects from stochastic events (e.g., storms and storm surges) during the breeding season. These results have been written up as a formal publication.
During the 2015/2016 breeding season, 60 SGDPs were banded and these individually recognizable birds presented a unique opportunity to assess population dynamics of this species. Therefore, continued banding and recapture efforts have become a priority during the 2016/2017 breeding season. During the first field trip of the 2016/2017 breeding season (late September to early October 2016), an additional 47 SGDPs were banded. Furthermore, 31 SGDPs were recaptured (21 from 2015/2016 breeding season, 3 from 2008/2009, 4 from 2004/2005 and 1 from 2003/2004). This data will form a solid foundation for a detailed study aimed at understanding the population dynamics and trends in the SGDP. Banding and recapture efforts will continue in upcoming field trips and breeding seasons to further compile the data.
The third aim, the assessment of the breeding biology of the SGDP on Codfish Island, is crucial to enable the continued existence of this species. Unfortunately, it was not possible to deploy the required study equipment (study burrows) during the first field trip due to logistical and bureaucratic constraints. Preliminary data on the breeding biology were collected during the first field trip (by assessing body condition of birds in the hand) and these data suggest prospecting to start in September, while incubation appears to start in the first week of October. Future attempts to place study burrows are currently being considered, as well as a study trial to assess the effects of study burrows on brood-chamber conditions (e.g., temperature and humidity).
In conclusion, the smooth progress of the analysis of the nest site selection of the SGDP on Codfish Island will enable more fine-tuned conservation strategies in the future. The first SGDP field trip of the 2016/2017 breeding season was a remarkable success in terms of capture-mark-recapture efforts. In addition, future field trips may enable the study of the breeding biology of this Nationally Critical species. I am thus very grateful for the support received from the Coastal Restoration Trust of New Zealand to further our understanding of a species in such desperate need of conservation management.
Posted: 1 November 2016 in the Flora & Fauna category