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Abstract

Ecological changes in the phenology and distribution of plants and animals
mediated by changes in the environment are occurring across the globe and have
been documented for a wide range of species. However, determining the specific
mechanisms that affect the life-history parameters of organisms is typically difficult.
Measuring population trends over time, and in relation to broad-scale
environmental state, is one of the simplest ways of linking the effects of physical
environmental variation to its direct effects on biological systems.
This study is concerned with describing key life-history parameters and population
demography of a wide-ranging and abundant pelagic seabird, the short-tailed
shearwater (Puffinus tenuirostris). The population demography of this uppertrophic
consumer is investigated directly within the context of its spatio-temporal
use of the marine environment and its response to environmental variation.
In this thesis I present data and analyses for:
1. Population trends of short-tailed shearwaters and the sympatrical/y
breeding little penguin (Eudyptula minor) - Trends from a colony of shorttailed
shearwaters at the southern most extent of their distribution were
documented from 2003-1 O and found to be declining at a rate of 15% per
annum. A series of hypotheses were constructed to provide possible
explanations for the observed trends including source-sink population
dynamics, recreational 'mutton-birding', by-catch from fisheries, investigator
effects, changes in onshore habitat characteristics, and distal changes in
food source availability. In contrast little penguins were found to be
increasing at a rate of 17% per annum with their increase attributed to the
removal of feral cats from Wedge Island in 2003.
2. The effects of investigator disturbance on short-tailed shearwaters and little
penguins - Researcher activities were monitored during the course of the
study to identify any possible effects on rate of egg laying, chick survival or
chick handling. No effect of the investigator was observed in short-tailed
shearwaters for any of life-history attributes measured with the effect of
investigators on little penguins unable to be conclusively determined.
3. The spatio-temporal use of the Southern Ocean during the breeding
season of short-tailed shearwaters - Geo-location devices were deployed
on 20 birds in the breeding seasons of 2004-05 and 2007-08. Foraging
locations and behaviours were identified over a temporal scale
encompassing the entire breeding season from the pre-egg laying
'honeymoon' period, to chick rearing. This study determined that trip
characteristics changed significantly over the duration of the breeding
season. Bimodal foraging strategies occurred once chicks had hatched
and the duration of long trips contracted from 20.1 ± 10.6 days to 14.6 ± 2.2
days. Foraging occurred in a range of water masses from the Australian
continental shelf to the Polar Frontal Zone with use of Southern latitudes
increasing over the course of the breeding season.
4. Identifying Annual variability in the diet of short-tailed shearwaters using
stable isotope analysis - Whole blood samples were collected over 4
breeding seasons and used to identify trophic foraging level and latitudinal
foraging location. Inter-annual differences in diet were observed during the
four breeding seasons with i513C and i515N values in 2004-05 and 2005-06
significantly higher than in 2006-07 and 2007-08. Despite the contrast in
diet between seasons, there was no direct relationship detected between
prey type and reproductive performance indicating that short-tailed
shearwaters are flexible in their response to changes in prey availability.
5. Influences of environmental variation on the population trend of short-tailed
shearwaters- After identifying specific spatio-temporal regions of
importance, this information was used to link physical oceanographic
parameters such as sea surface temperature (SST), primary productivity
(Chia), wind speed and direction, sea surface height (SSH), sea surface
height anomaly (SSHa) and ice edge extent to the decline in breeding
short-tailed shearwaters. While no relationships were determined between
chick survival and environmental variables, we detected a relationship
between a decline in egg laying and an increase in pre-egg laying sea
surface height anomaly (SSHa) in the Southern Ocean.
General discussion and recommendations for future research-Understanding the
causal mechanisms driving changes in population demography is complex.
Changes are often subtle and may be interconnected. By utilising multidimensional
approaches including telemetry, diet and physical oceanography,
improvements can be made in determining the links between the marine
environment and upper trophic consumers. As environmental changes may affect
different demographic parameters and the response variables may be direct ( i.e.
an increase in adult mortality or a decrease in adults choosing to breed) or lagged
(i.e. reductions in breeding success), it is likely that multiple processes are
contributing to the decline of shearwaters on Wedge Island. This colony should
continue to be monitored, in addition to others within the species distribution as
only long-term data sets will determine if this is part of an oscillation in breeding
numbers or a response to more long-lasting shifts in environmental conditions.
Chick diets should be obtained in addition to adult diet corresponding to the preegg
laying period. Marking of birds within the colony will assist in making stronger
conclusions as to the effect of emigration. Further telemetry studies will aid in
detecting inter-annual differences in foraging behaviours.

Item Type:	Thesis - PhD
Authors/Creators:	Vertigan, CA
Keywords:	Short-tailed shearwater, Little blue penguin
Copyright Holders:	The Author
Copyright Information:	Copyright 2010 the author
Additional Information:	Thesis (PhD)--University of Tasmania, 2010. Includes bibliographical references. Contrasting populationtrends in two sympatic seabirds (short-tailed shearwaters, Puffinus tenuirostris and little penguins, Eudyptula minor) in south-east Tasmania -- Investigator disturbance in short-tailed shearwaters (Puffinus tenuirostris) and little penguins (Eudyptula minor) -- Spatio-temporal use of the Southern Ocean by breeding short-tailed shearwaters (Puffinus tenuirostris)-- Variability in the adult provisioning diet and reproductive performance of a pan oceanic predator; the short-tailed shearwater (Puffinus tenuirostris) -- Detecting trends between environmental variation and the population trends of short-tailed shearwaters in south-east Tasmania
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