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Feeding ecology and free-living energetics of the little penguin, Eudyptula minor, in Tasmania

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Gales, Rosemary,1960- (1989) Feeding ecology and free-living energetics of the little penguin, Eudyptula minor, in Tasmania. PhD thesis, University of Tasmania.

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Abstract

Of all birds, penguins are the most specialised in terms of their adaptations to a
marine lifestyle. The little penguin, Eudyptula minor, is the smallest of all the penguin
species and holds an important position in the functioning of the marine ecosystems
across its range. To examine the role of penguins in the marine environment it is
essential to have information concerning their food and energy requirements, and how
these change in space and time. In this study, the feeding ecology and free-living
energetics of little penguins in Tasmania was examined by investigating their diet,
energy and food consumption rates and their behaviour at sea. Where possible, this
information was collected over the annual cycle, and combined with population
estimates in order to assess the population requirements of little penguins in Bass
Strait, the stronghold of the species distribution in Australia.
Information on the diet was collected by stomach flushing penguins over a two
year period at three sites around Tasmania. The stomach flushing technique was first
validated by feeding trials and was found to be effective in collecting complete stomach
contents provided penguins were flushed repeatedly until only clear water is ejected.
The stomach samples collected from the penguins were often highly digested and so
extensive use had to be made of diagnostic remains from prey items in order to
quantitatively determine the species composition of the diet, as well as the size of prey
items consumed. It was evident that fish were important in the diet and the validity of
using the otoliths from fish to determine the number and size of fish consumed was
tested by feeding trials and subsequent retrieval and examination of the penguin
stomach contents. This showed that the rate of digestion of otoliths decreased with
meal size but increased with time after ingestion, and only otoliths which are not
affected by digestion should be used to assess the original size of the fish consumed.
Fish were the most important prey taxon consumed by little penguins in terms of
frequency of occurrence, numbers, mass and energy contribution, with cephalopods
and crustaceans contributing to the diet to a lesser degree. The diet of the little penguin
in Tasmania showed local, seasonal and annual changes which probably reflects the
local availability of the prey species. There was no difference in the diet or stomach
content mass between male and female penguins, the sex of penguins being determined
on the basis of beak morphology, which was shown to be a reliable criterion. The prey
of little penguins was characterised as being small, schooling species which occur in
relatively shallow water, consistent with the foraging behaviour of the penguins.
The behaviour of little penguins at sea was studied using a new archival
electronic activity recorder and the results showed that foraging occurred mainly in the
top 15 m, at mean swimming speeds of between 8 to 9 km h -1 . Characteristics of searching and foraging behaviours were hypothesised on the basis of speed and depth
profiles. In interpreting the swimming behaviours the effect of carrying the electronic
recorder was assessed by simultaneously measuring the water and energy flux rates via
isotope turnover techniques. This showed that there were significant effects of carrying
instruments while foraging, and these effects were evident even when the devices
constituted as little as 0.1 % of penguin mass, or 1.4 % penguin cross-sectional area.

The accuracy of the isotope turnover techniques was assessed by comparing
estimates of water, sodium and energy turnovers determined from tritium, sodium-22
and doubly labelled water turnovers in captive little penguins with estimates from
simultaneous materials balance trials. This validation allowed the identification of
appropriate equilibration times and turnover rate requirements for all three isotopes
which have to be met to ensure reliable results from the use of the isotopes in field
studies. In conjunction with analyses of the water, sodium and energy status of a
variety of little penguin prey items, these trials also provided information on energy
assimilation rates which are required for the conversion of water, sodium and energy
flux rates into food and seawater consumption rates.

The metabolic rates and food consumption rates of free-living little penguins in
Bass Strait were studied over the annual cycle. These estimates of energy turnover
during both breeding and non-breeding activities were used to construct time/energy
budgets. The period of highest energy demands occurred during chick-rearing which
occupies only 16 % of the annual time budget, but requires 31 % of the annual energy
budget. Another energetically expensive period also occurs over the winter nonbreeding
period when adult energy expenditure exceeds the net energy gain acquired
from feeding. Over the annual cycle, non-breeding birds require ca. 477 500 kJ and
breeding birds require ca. 533 500 kJ, which when coupled to information on the diet
and energy content of the dietary items, translates to 115 and 137 kg of food penguin -1
year-1 . When combined with the size of the little penguin population in Bass Strait, I
estimated that ca. 37 000 tonnes of food are consumed by little penguins each year,
which comprises 25 000 tonnes of fish, 11 000 tonnes of cephalopods and 1 000 of
tonnes crustaceans. All facets of this study, detailing the diet, foraging behaviour and
food and energy requirements were synthesised to identify the critical periods with
respect to the dynamics of little penguin energy and food acquisition rates and the
vulnerability of little penguins to fluctuations in food availability, resulting from either
natural perturbations or from commercial fishing activities.

Item Type: Thesis (PhD)
Keywords: Little blue penguin, Little blue penguin
Copyright Holders: The Author
Copyright Information:

Copyright 1989 the Author – The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1990. Includes bibliographies. Journal articles in pocket at back of vol

Date Deposited: 09 Dec 2014 00:15
Last Modified: 17 Aug 2016 00:37
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