Effects of Habitat Fragmentation on Swallowtail Butterflies

By Jenna Siu, Department of Biology, University of Western Ontario

Jenna Siu is a M.Sc. Candidate in the Environment
and Sustainability Collaborative Program,
Department of Biology,
The University of Western Ontario, London, Ontario
Research was done under the supervision of
Dr. Daria Koscinski and Dr. Nusha Keyghobadi.
The following is a brief summary of Jenna’s
research work.

Background:

In southern Ontario some of the most threatened
habitats occur in the Carolinian Zone, where major
portions of prairies, savannahs and forests have
been destroyed. These changes to the natural
landscape have caused habitat loss and
fragmentation; the breaking up of habitat into
smaller patches creating more edges, or the
boundary between two land cover types. Habitat
fragmentation has been shown to have harmful
impacts on native populations (e.g. the Acadian
Flycatcher, the American Badger, and the Grey
Ratsnake). To understand how species are affected
by fragmentation, we need to know how they
respond to edges, where some species avoid them
while others may prefer them.

For my master’s research, I studied the effects of
habitat fragmentation on two butterfly species, the
Eastern Tiger (Papilio glaucus) and the
Spicebush (P. troilus) Swallowtails in Norfolk
County, Ontario. These species have a unique
habitat requirement because they use two different
habitat types (e.g. forests and meadows). They
require forest species such as tulip trees,
spicebush, and sassafras to lay eggs on as well as
flowers in meadows for nectar. The distribution of
their resources in forests and in meadows predicts
that they will be concentrated at forest edges to be
able to access both resources. This is also known
as a positive edge response.

What I did:

With the help of many of the local residents offering
their properties for field sites, volunteers and my
field assistants Sarah Kruis and Ryan Smith, I was
able to test the positive edge hypothesis for these
swallowtail butterflies.

During the summer of 2013, I surveyed their
abundance along paths that spanned forests, forest
edges, and meadows. In 2012, I also examined
their flight orientation by capturing and releasing
butterflies at various distances in meadows and in
forests and tracking their movement using a
handheld GPS.

What I found:

My results show that the presence of forest edge is
an important feature in the landscape for these
butterflies. Both species are more abundant at or
near the edge and fly towards the edge when
released from distances from both forests and
meadows. I did find differences between the two
species; the Eastern Tiger swallowtails exhibited a
much clearer edge response than the Spicebush
swallowtail. I also found differences in the flight
orientations between males and females, where
males had more direct flights than females.

The big picture:

My study demonstrates that these swallowtails may
be reliant on the forest edge, which provides
accessibility to these two habitat types. This would
make them edge species, in contrast to the
generalist, or woodland species they are
considered to be. Therefore, some degree of forest
fragmentation may actually be beneficial to native
species and should be considered in land
management plans.

Acknowledgements:

Nature Conservancy of Canada, Long Point Regional
Conservation Authority, Long Point Waterfowl Research
and Education Center, local land owners, volunteers,
and field assistants

For more information, you can contact me at
jenna.c.siu@gmail.com.