The effects of urbanisation on the feeding ecology and physiology of mallards, Anas platyrhynchos : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Zoology at Massey University, Palmerston North, New Zealand
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Date
2019
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Massey University
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Abstract
In this thesis, I address the extent of wildlife feeding (of Mallards, Anas platyrhynchos) in an
urban park, and evaluate whether there are discernible differences in body composition and health
between urban and rural Mallards. With an increasingly urban human population, more people
are engaging with wildlife at their local parks by feeding. Although similar studies have been
conducted exploring the participation rates of wildlife feeding in Australasia, this is the first study
to my knowledge that quantitatively explores the degree of anthropogenic food being offered to
Mallards through wildlife feeding in an urban park, and the impacts the foods on offer have on
the physiology and health of Mallards.
I surveyed wildlife feeding at the Victoria Esplanade pond in Palmerston North, a frequently
visited site for urban feeders. I documented the types and amounts of food being given to ducks,
and the basic demographic structure of the party (numbers of adults and children) on weekdays
and weekends in late summer and early winter 2018. Results showed that feeding activity was
highest on weekends, was most often done by 1–2 adults with 1–2 children, and usually consisted
of commercial bread, though a wide range of foods was offered. Not unexpectedly, bread offered
tended to be of cheaper brands. When food was offered, the large majority of ducks present
attempted to eat it, but natural foraging was also present throughout the day. Counts and GPS
tracking of two ducks indicate that many birds leave the pond at night, presumably to forage on
natural food sources elsewhere.
To determine if living in an urban environment affects the physiology and health of Mallards, I
compared the body composition of urban and rural ducks. Reliance on anthropogenic food that is
low in fibre and high in carbohydrates could result in birds having smaller digestive organs and
higher fat levels, with associated health issues. Instead, I found that urban birds had larger
gizzards and caeca, while rural birds had larger flight muscles. These differences may reflect other
aspects of the birds’ environments and behaviour than anthropogenic feeding. Birds in Victoria
Esplanade are known to feed on acorns and palm tree seeds, which likely require a large gizzard,
and rural birds probably have higher flight activity than urban birds (resulting in larger flight
muscles). Longer caeca in urban birds are unlikely to reflect higher cellulose breakdown needs
but could potentially relate to higher immunosurveillance in a high-density pond situation. No
other health differences were observed.
Together, these results indicate that Mallard physiology is responsive to local conditions, but at
the current level of wildlife feeding there appear to be no major health impacts on individuals.
The study site does, however, have a diverse environment with other food sources (including a
nearby river) and impacts could be greater in truly ‘urban-locked’ pond sites.
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Keywords
Mallard, Effect of human beings on, New Zealand, Palmerston North, Feeding and feeds, Physiology