Avian Dietry Preferences

To: Birding-Aus Mail <>
Subject: Avian Dietry Preferences
From: Laurie & Leanne Knight <>
Date: Fri, 15 Jun 2001 16:51:44 +1000
Here's some research findings to chew on ...

 Monash Newsline  : Front Page

 Birds play key role in local habitats

 June 2001

 Birds are as picky as people when it comes to choosing which fruit to
eat, according to a Monash University researcher.

 While it may appear that birds are happy to eat anything they can get
their beak into, the Department of Biological Sciences research shows
that there is much more decision-making involved than is otherwise

 The study could help scientists better understand the role of birds in
seed dispersal and vegetation regeneration.

 According to Ms Margaret Stanley, author of the thesis 'Factors
influencing fruit choice and seed dispersal by the silvereye', a number
of issues affect which fruit a bird will choose to ingest.

 Findings from the research suggest that birds are concerned with fruit
quality in terms of profitability - weighing up the expenditure of
energy required to eat the fruit with the quality of its pulp and the
size of the seed they are likely to ingest if they eat it whole.

 "If the fruit is one they can swallow whole, it is a catch-22 situation
for the bird. They must decide whether the quality of the pulp outweighs
the seeds ballast that will fill up their gut and prevent them from
eating more food until the seeds pass through their system," Ms Stanley

 "The birds also showed preference towards sitting next to or reaching
up to a fruit rather than hanging upside down to ingest it, as this
action was much more energy expensive."

 While the research covered many bird species, much of the study
concentrated on the silvereye (Zosterops lateralis), a small bird
commonly found in south-eastern Australia - and a prolific fruit eater.

 "In fruits that were translucent, such as those on the native saltbush,
the silvereyes actually chose the ones that they could see had smaller
seeds. Tests done on these seeds, after recovery from the birds faeces,
showed that they were not destroyed while in the gut and still had the
ability to germinate."

 The study, while concentrating on bird behaviour, has broader
application for better understanding the part that various bird species
play in seed dispersal, an important activity for the spread and
regeneration of vegetation.

 "Birds are considered the most important dispersers of seeds of
fleshy-fruited plants, particularly in temperate regions, but their
effectiveness at this depends firstly on the probability that they will
ingest a particular fruit and the seeds it contains," Ms Stanley said.

 "Silvereyes are good dispersers of native fruits, as long as they can
swallow them, otherwise all they are doing is robbing the pulp and not
dispersing the seeds. The silvereyes were particularly remarkable at
avoiding even the tiniest seeds in large fruits."

 Fruiting plants are commonly used to attract birds that will aid the
regeneration of vegetation on building and mine sites. Having a better
understanding of which fruits are most attractive to birds as well as
which seeds they will best disperse can ensure this process remains both
efficient and effective.
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