An Analysis of The Differences In The Frequency of Prey Items Caught by Maryland Owls

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An Analysis of The Differences In The Frequency
of Prey Items Caught by Maryland Owls

• A Research Proposal
• Matt Bostick

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Background Owls of Maryland

• Five species of owls live in or pass through
  Maryland.
• Barn owls
• Great Horned owl
• Barred owls
• Eastern Screech owl
• Northern Saw-whet owl

Barred Owl
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Adaptations as predators

• Owls have special adaptations that enable them to
  hunt at night.
• 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
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Owls as predators

• Owls rely on silent flight to surprise their
  prey.
• The shape of the owls flight feathers muffles
  the sound wind makes as it flows past them.

Saw-Whet Owl
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An idealized food pyramid
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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.

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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.

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Owl Pellets

• I examine owl 3 owl pellets from each species in
  order to estimate the frequency of prey items
  eaten.

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Species diversity has two components

1. Species richness how many different species are
   present in a habitat
2. Relative Frequency total number of individuals
   of each species present given in

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1. Shrew
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2. Vole
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3. Mouse
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4. Squirrel
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5. Gopher
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6. Rat
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7. Bird
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Hypothesis

• I hypothesize that the frequency of prey items
  found in the owl pellets will be significantly
  different between species.

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Materials

• I need
• 3 Owl Pellets from each species
• Dissecting Pan
• Forceps
• Probe
• Metric Ruler
• Bone Identification Sheets
• Gloves

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Methods- Bone Sorting Chart
Common Name Genus 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
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Type and of bones Vole Shrew Mole Rat Mice Bird
Skulls
Jaws
Shoulder blade
Front legs
Hips
Hind legs
Assorted ribs
Assorted vertebrae
of animals
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Chi-Square

• is a statistical test used to determine whether
  your experimentally observed results are
  consistent with your hypothesis.

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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)

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Our final formula
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

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I will use a table to assist in my data
organization.
Species of Owl Observed Voles Expected Voles O-E (O-E)2 (O-E)2 E
Great Horned 6 4 2 4 1
Screech 5 4 1 1 0.25
Barn 1 4 -3 6 1.5
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Chi Square Critical Values
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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.

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