An Analysis of
The Differences
In The Frequency
of Prey Items
Caught by
Maryland Owls
A Research Proposal
Matt Bostick
Background: Owls of Maryland
Five species of owls
live in or pass through
Maryland.
1. Barn owls
2. Great Horned owl
3. Barred owls
4. Eastern Screech
owl
5. Northern Sawwhet owl
Barred Owl

Owls have special
adaptations that enable
them to hunt at night.
Adaptations as
predators
Large and fixed eyes with
binocular vision and good
depth perception.
Owls have developed an
incredibly flexible neck that
allows them to turn their
head 270 degrees in both
directions.
Their eyes are also extremely
light sensitive, allowing them
to see well at night.
Barred Owl
Owls as predators
Owls rely on silent
flight to surprise their
prey.
The shape of the
owl’s flight feathers
muffles the sound
wind makes as it
flows past them.
Saw-Whet Owl
An idealized food pyramid
Owl Pellets – What Are They?

Owls do not have teeth for grinding and
cannot pass whole bone and claws through
their digestive tract safely.

The protein enzymes and strong acids that
occur in the digestive tract of raptors do not
digest the entire meal.

The relatively weak stomach muscles of the
bird form the undigested fur, bones, feather
etc. into a bolus (or wet slimy pellets).

The undigested portions may include beaks,
claws, scales, or insect exoskeletons.
Purpose:
 To
analyze the frequency of
prey items caught by the 5
species of owls common to
Maryland
 To determine if the frequency of
prey items is significantly
different between the species
observed.
I
examine owl Owl Pellets
3 owl pellets
from each
species in
order to
estimate the
frequency of
prey items
eaten.
Species diversity has two
components:
1. Species richness:
1. Shrew
33%
2. Vole
18%
3. Mouse
17%
4. Squirrel
14%
5. Gopher
8%
6. Rat
6%
7. Bird
4%
how many different
species are present
in a habitat
2. Relative Frequency:
total number of
individuals of each
species present
given in %
Hypothesis
I
hypothesize that the
frequency of prey items
found in the owl pellets will
be significantly different
between species.
Materials
I
need:
3
Owl Pellets from
each species
 Dissecting Pan
 Forceps
 Probe
 Metric Ruler
 Bone Identification
Sheets
 Gloves
Methods- Bone Sorting Chart
Common Genus
Name
Freq
Found
Vole
Microtus
70%
Shrew
Sorex
20%
Mole
Scapanus
5%
Deer
Mouse
Peromyscus 2%
House
mouse
Mus
2%
Rat
Rattus
1%
(small
bird)
Hirundo
rare
Type and
Vole
# of bones
Skulls
Jaws
Shoulder
blade
Front legs
Hips
Hind legs
Assorted
ribs
Assorted
vertebrae
# of
animals
Shrew
Mole
Rat
Mice
Bird
Chi-Square
is a statistical test used to determine
whether your experimentally
observed results are consistent
with your hypothesis.
When using chi-square in
biology, there is some
vocabulary we must know:
 Hypothesis
= a proposed explanation of an
observed phenomenon
 Observed
results = what you can observe
during the course of an experiment
 Expected
results = what you expect to see
based on your hypothesis (predictions)
The formula includes:
 X2 =
chi-square
 (o - e) = observed minus expected
[sometimes you may see this represented with a d which
means the difference between the expected and observed
results]
e
= expected results
 o = observed results
and 
= sum of
Our final formula:
x  (
2
( o e )
e
2
)
I will use a table to assist in my
data organization.
O-E
(O-E)2
(O-E)2
E
4
2
4
1
5
4
1
1
0.25
1
4
-3
6
1.5
Species of Owl
Observed
Voles
Expected
Voles
Great Horned
6
Screech
Barn
Chi – Square Critical Values
Expected Results
I
expect that the results from
my chi-square analysis will
indicate that significant
differences in the frequency
of prey items will exist
between the 5 owl species
studied.
Frequency of Prey Items Caught by 5
Species of Maryland Owls
14
Frequency
12
10
saw whet owl
schreech owl
great horned owl
barn owl
barred owl
8
6
4
2
0
squirrels
rat
bird
gopher mouse
Prey Item
vole