Transcript Owl Pellet overview presentation File

Barn Owl Pellet Survey
Using Owl Pellets to Illustrate Energy
Transfer from Prey to Predator
Webs of Life: Food Webs and Trophic Cascades
February 19, 2011
Food Chains Versus Food Webs
Food Chain
One path of
energy flow
Food Web
Multiple pathways and
everything is connected
Biomass
Barn Owl
Traditional Barn Owl Pellet Activity
Part 1: Energy Flow and Food Webs in Ecosystems
Objectives:
• Dissect barn owl pellets
• Use “Key to Skulls” to identify animal skulls found in pellets
• Use classroom findings to determine the average number of prey
items per pellet
• Estimate the food mass that the owl consumed
Procedure
1. Work in pairs or small teams and set up your workstation with paper
towels, toothpicks, probes, tweezers, ruler, magnifying glass and an
owl pellet.
2. Before dissecting your pellet record the length, width (at its widest
point) and remove the foil wrapping before weighing your owl pellet.
Barn Owls
• Ecologists study living organisms and their
relationship to their environment.
• In a biotic community the existence of each
population is influenced by the presence of all the
other organisms.

This association has an effect in both directions of
the food chain or web.
• In this exercise we will use the Barn owl as a
representative organism to learn more about
energy flow and food webs in an ecosystem.
Barn Owls
• Barn owls (Tyto alba) along with hawks and eagles
belong to a group of birds known as “raptors” or
birds of prey.
• To minimize interspecies competition each of these
birds are uniquely adapted to hunt in different
habitats, different prey, at different times of day.
Barn Owl
Description
• Golden-rust color with black
flecks and a white facial disk
• Forward oriented eyes, large
hooked beak, long hooked
talons
• 31-39 cm (12-15 inches) long
from head to tail
• 460-580 g (1-1.25 pounds)
• Adults are monogamous for
life
• 44 inch wing span
Barn Owl Habitat
• Range: Found throughout
most of the world. Absent
primarily in regions with long
dry or cold seasons
• Open country (pastures,
prairies and grasslands, brush,
swamps and forests) Large
open regions which support
an abundance of small
rodents (such as agricultural
regions in northwestern and
southeastern U.S.)
• Often found in man-made
structures (barns, church
steeples)
forest
Distribution of Tyto alba
swampland
grassland
Barn Owl Hunting and Diet
• Nocturnal hunters
• Complete carnivores – prey varies with on
the owl’s habitat but includes insects,
frogs, snakes, mammals (most often voles,
pocket gophers) and birds
• Often swallow its prey whole
• Flesh and soft parts are digested and
passed to the intestines for absorption
• Non-digestible parts (bones, teeth, fur,
feathers and chitin from insects) are
compressed into a pellet and regurgitated
Barn Owl Reproduction
• Barn Owls do not build a straw
nest. Instead the regurgitated
pellets get trampled into a pile
in which eggs are deposited.
• 1-13 eggs, eggs are laid at two
day intervals.
• Only females incubate eggs.
Incubation starts with the first
egg and lasts 30-31 days.
• Hatching: occurs at 2-day
intervals. Nestlings are
featherless and blind, requiring
the mother to feed them.
Barn Owl Pellets
• By examining the contents of
the black pellets we can gain
information about

the owl’s seasonal and regional
diet and habitat differences.

The pellets can also effectively
illustrate the nature of the food
chain in which the owl is a
predator.

learn more about energy flow
and food webs in an ecosystem.
Owl Pellet Survey
Energy Transfer from Prey to Predator
http://www.mammal.org.uk/index.php?option=com_content&view=article&id=255&Itemid=288
• The National Owl Pellet Survey Report
• Analyses owl pellet batches from throughout the UK and records the results
on a computer database.
• The data are then used to support the objectives of the survey and other
research
• The vast majority of the pellets are from the Barn Owl (Tyto alba)
•
http://www.mammal.org.uk.indexphp?option=com_content&view=article&id=255&Itemid=288
Owl Pellet Survey
Energy Transfer from Prey to Predator
Introduction
• Trophic levels describe
the feeding
relationships within a
community.
• Energy pyramids are
used to represent
important aspects of
trophic level
interactions
Materials and Methods
• Ordered from a number of
educational resources
(e.g., Wards, Genesis Inc.)
• Comparison groups from
Northwestern and
Southeastern US.
Owl Pellet Survey
Energy Transfer from Prey to Predator
Part 1: Identification of Small
Mammal Prey Items
• Visually sort skull and jaw
bones to more easily identify
the specimens
• Collections include pellets
from Northwestern and
Southeastern United States.
Owl Pellet Survey
Energy Transfer from Prey to Predator
Helpful information:
• 3 main types of small mammalian prey:

two types of rodents (voles and mice), and

Insectivorous prey (almost all are shrews)
are found in owl pellets.
• Details of the tooth and root patterns
allow identification to species.
• Large differences are seen between the
molar teeth, tooth and root patterns of
the two rodent subfamilies.
• The teeth of shrews species have red
tips.
Owl Pellet Survey
Energy Transfer from Prey to Predator
• Arranges specimens as seen in the figure below (skull,
left and right jaw) for each prey type.
Owl Pellet Survey
Energy Transfer from Prey to Predator
Part 2: Results by Number of Prey Items
• Once identification has been made, record the number of
each prey type found (based on the number of skulls or
paired jaw bones) on the Table 1A and/or Table 1B.
• Determine the Percent of Diet (i.e., availability of the prey
species to the owl) by dividing the number or prey
Frequency Found (n1) for each species by the Total
number of prey found. Record your values on the column
labeled Percent of Diet on the appropriate tables.
Owl Pellet Survey
Energy Transfer from Prey to Predator
Mean
Mass (g)
Conversion
Factor
(b)
Vole
40
2
Mouse
20
1
Mole
55
2.75
Shrew
5
.25
Rat
240
12
Bird
40
2
Gopher
240
12
Site
Northwest
Frequency
Found
(n1)
Percent of
Diet
Biomass
Units
(n*b) = B1
100%
(TB1)
Percent
Biomass
(B1/TB1)
TOTALS
100%
Determine the Percent of Diet (i.e., availability of the prey species to the owl) divide the number or prey
Frequency Found (n1) for each species by the Total number of prey found. Record you values in the
column labeled Percent of Diet on the appropriate tables.
Owl Pellet Survey
Energy Transfer from Prey to Predator
Part 3: Results by Food Value
• Determine the biomass that each prey represents in the diet of
the barn owl.
• The importance of a given prey species to the owl diet depends
not only on the relative number of individuals of the species
consumed, but also on the typical body weight of the species.
• That is to say there is a difference between the “food value” (the
energy) derived from a shrew (average mass 2 grams) as
apposed to a vole (average mass 40 grams).
Owl Pellet Survey
Energy Transfer from Prey to Predator
•
To determine how much each prey group contributes to the total intake of the owl food web…
•
First - take the average mass of each prey groups and expressing it in terms of biomass of prey
consumed.
•
This calculation is done by taking the number of individuals in each prey group (n1) and
multiplying it by the biomass conversion factor (b).

The conversion factor is a standardized unit based on the assumption that a 20 gram mammal has a biomass
conversion factor of 1.0.
•
This number is the biomass.
•
The percent biomass is calculated by dividing the biomass for each prey group (B1 or B2) by the
total biomass (TB1 or TB2) respectively.
Mean
Mass (g)
Conversion
Factor
(b)
Vole
40
2
Mouse
20
1
Mole
55
2.75
Shrew
5
.25
Rat
240
12
Bird
40
2
Gopher
240
12
Site
Northwest
Frequency
Found
(n1)
Percent of
Diet
Biomass
Units
(n*b) = B1
100%
(TB1)
Percent
Biomass
(B1/TB1)
TOTALS
100%
Owl Pellet Survey
Energy Transfer from Prey to Predator
• Some Anatomy
Zygomatic Arch
Infraorbital opening
Auditory meatus
Diestema
Molarifomr teeth
Zygomatic Arch
Birds
Caprimulgus carolinensis (Chuck-will's-widow)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Aves
Order: Caprimulgiformes
Family: Caprimulgidae
Genus: Caprimulgus
Species: Caprimulgus carolinensis
Birds
Caprimulgus carolinensis (Chuck-will's-widow)
Shrew
Blarina brevicauda (northern shorttailed shrew)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Soricomorpha
Family: Soricidae
Northern short-tailed shrew
Blarina brevicauda
Weasel
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Carnivora
Suborder: Caniformia
Family: Mustelidae
Mustela frenata
(long-tailed weasel)
Long tailed weasel
Mustela frenata
Moles
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Soricomorpha
Family: Talpidae
Mole trails and tunnel entrances
(such as these) can be a reliable way
to track and identify moles.
Moles
Moles
Scalopus aquaticus (eastern mole)
Rabbits and Hares
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Lagomorpha
Family: Leporidae
Sylvilagus nuttallii
(mountain conttontail
Sylviagus audubonii (Audubon’s cottontail)
Lepus americanus (snowshoe hare)
Rabbits and Hares
Lepus americanus (snowshoe hare)
Rabbits and Hares
Lepus americanus (snowshoe hare)
Pocket Gophers
Family Geomyidae
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Castorimorpha
Family: Geomyidae
Geomys breviceps (Braid’s pocket gopher)
Pocket Gopher
Orthogeomys heterodus (variable pocket gopher)
Pocket Gopher
Orthogeomys heterodus (variable pocket gopher)
Vole
Microtus ochrogaster (prairie vole)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Myomorpha
Family: Cricetidae
Subfamily: Arvicolinae
Genus: Microtus
Species: Microtus
ochrogaster
Vole
Microtus ochrogaster (prairie vole)
Vole
Microtus pennsylvanicus (meadow vole)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Myomorpha
Family: Cricetidae
Subfamily: Arvicolinae
Genus: Microtus
Species: Microtus pennsylvanicus
If you see small openings in the grass that lead to mousesized tunnels both in the grass and into the ground, then
you've found the home and foraging area of a vole.
Vole
Microtus pennsylvanicus (meadow vole)
Mice
Mus musculus (house mouse)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Myomorpha
Family: Muridae
Subfamily: Murinae
Genus: Mus
Species: Mus musculus
Mice
Mus musculus (house mouse)
Rattus rattus
(house rat)
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Myomorpha
Family: Muridae
Subfamily: Murinae
Genus: Rattus
Species: Rattus rattus
Rat
Rattus rattus (house rat)
Batch of barn owl pellets ready for processing
Skull & jaw bones sorted and
awaiting identification
Bank Vole
Wood Mouse
Common
Shrew
Harvest Mouse
Field Vole
Water Shrew
Pygmy
Shrew
Owl vid #1
Owl vid #2