APS 209 Animal Behaviour

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APS 209 Animal Behaviour
Lecture 9 The Evolution of Feeding Behaviour

• Search Images
• Social Foraging Insects, Birds, Mammals
• Selecting What to Eat Costs and Benefits

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Aims Objectives
Aims 1. To describe how animals may help each
other in foraging, particularly by sharing
information. 2. To present a special reading that
builds on the discussion in the chapter. 3. To
introduce cost-benefit analysis and
optimality. Objectives 1. To understand why some
animals living in social groups may not be
selected to transfer information deliberately. 2.
To understand the logical basis of cost-benefit
analysis and optimality, and learn some examples.
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Search Image
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Finding Food Search Image
How do predators find their food? Predators and
prey are often locked into a co-evolutionary
struggle. Prey may evolve to be harder to find
and predators better at detecting
prey. Tinbergen observed the following. When a
certain type of caterpillar started to appear in
Dutch woodlands, breeding songbirds rarely
brought it back to their nests. But once a few
had been brought back, the birds started to
collect them at a far greater rate. It was as if
the birds had come to recognise the subtle visual
characteristics and had formed a search image.
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Search Images in Humans
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Testing the Search Image Hypothesis
Pietrewicz and Kamil used operant conditioning
using blue jays and moths to investigate whether
search images occur. Captive blue jays were
shown 16 slides, 8 of which had a cryptic moth
positioned on an appropriate background. In 1
series, the 8 moths were same species. In the
other, 2 species of moth with different colour
patterns and resting positions appeared in random
order.
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Testing the Search Image Hypothesis
The birds performance improved when presented
with one species or the other, but not when given
both species.
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Olfactory Search Image
Humans are primarily visual creature. This can
cause us to be vision-centric when we consider
animal behaviour. This is something you must
train yourself not to be. Think about the sensory
world of any animal that you are studying. Some
animals use their sense of smell to find food and
may also form the equivalent of a search image
but for smells. Or at the least they may learn to
associate a particular smell with food.
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Finding Food By Smell in Skunks
Striped skunk is nocturnal and forages at night.
It locates food by odour. Young hand reared
skunks were allowed to forage for dry dog food in
an outdoor enclosure. Food was located at greater
and greater distances as they gained experience.
Orientation behaviour was shown by its
distinctive posture, with nose held high and
direct march to food.
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Finding Food By Smell in Skunks
Maximum distance over which is detected also
increases.
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Lizard Foraging Evolutionary History
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Social Foraging
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Getting Help from Companions
Animal Groups as Information Centres Social
Insects Groups (colonies) composed of related
individuals Cooperation is strongly favoured by
natural selection (kin selection/inclusive
fitness). Deliberate communication with
nestmates. Methods include waggle dancing,
direct leading, pheromone trails. Other group
living animals Groups normally composed of
mostly unrelated individuals. Cooperation less
strongly favoured by natural selection (kin
selection/inclusive fitness). Incidental
communication with conspecifics. Methods
observing foraging orientation of successful
foragers Other foraging advantages of being in
a group Take prey much larger than
themselves wolves taking moose or army ants
large arthropods or other insect colonies.
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Social Foraging Waggle Dance and Communication
Information
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Getting Help From Companions
Social Insects Groups (colonies) composed of
related individuals. Cooperation is strongly
favoured by natural selection (kin selection,
inclusive fitness). If worker A helps worker B
gather more food this is as good to worker A as
collecting more food herself, as the food comes
back to the same nest. Workers may help each
other in capturing prey (e.g., army ants), or
defending a food patch (ants, some stingless
bees). The most common means of helping each
other is by communicating the location of food to
nestmates. There are many methods including
waggle dances in honey bees and direct leading
and pheromone trails in ants.
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Honeybee Foraging
Honeybees forage for pollen, nectar, water and
propolis Workers that have found a good source of
pollen or nectar communicate the location to
nestmates by a dance
If food is close (lt50m), the bees perform a
round dance
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The Waggle Dance
If food is more distant, then foragers perform a
waggle dance
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The Waggle Dance
In the nest, the dances are performed on vertical
combs in darkness
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(No Transcript)
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The Waggle Dance
Dancer (forager)
Dance Followers (unemployed foragers)
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Waggle Dance Communicating Direction
In a fan test Karl von Frisch trained scout
bees to a feeder at F. He then put out feeders of
equal attractiveness at all 7 feeding stations
and counted the recruits. More arrived at the
advertized location, F, than other equidistant
locations.
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Waggle Dance Communicating Distance
Train bees to a feeder 750m from hive. These bees
dance in the hive. Capture recruits at feeders at
different distances in the same direction. The
training distance gives most recruits.
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Removing Directional Information
Honey bee foragers will dance on horizontal
combs. They will orient the dance to light
instead of to gravity if there is a strong
directional light source. But if there is no
directional light source they will dance in
random directions. By making the combs horizontal
(which they are not in nature) and having no
directional light source it is possible to remove
the directional information provided in the
dances. In this way, it is possible to compare
the recruitment to a food source of bees from
normal hives, with informative dances, to bees
from horizontal hives where dances are
non-informative.
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Removing Directional Information
A larger proportion of the recruits come to the
advertized site when combs are vertical.
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Removing Directional Information
Recruits are more tightly bunched around
advertized site when combs are vertical than
horizontal.
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Benefits of Waggle Dance
By following waggle dances, honeybee foragers do
not find flowers faster. But they do find better
quality flowers. This is because only bees who
are working a high quality patch of flowers make
dances.
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Social Foraging How Waggle Dance Improves Colony
Foraging
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Special Reading Honeybee colonies achieve
fitness through dancing
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Does Dancing Improve Foraging?
Test by comparing the weight gain in hives with
waggle dances without waggle dances Problem
It is not possible to prevent dancing. Solution
It is possible to cause disoriented dancing (no
direction information). Method Compare the
weight gain in hives with correctly oriented
waggle dances with disoriented waggle
dances Prediction hives with oriented waggle
dances collect nectar more efficiently, leading
to greater weight gain. Sherman, G., Visscher, P.
K. 2002. Honeybee colonies achieve fitness
through dancing. Nature 419 920-922.
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Observation Hives Used
V. Vertical
O. Oriented Light (Horizontal)
D. Diffuse Light (Horizontal)
Foragers in horizontal observation hives with
diffuse light make disoriented dances. Those in
vertical hives or horizontal hives with oriented
light correctly oriented dances.
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Does Random Dancing Affect Recruitment?
Syrup feeder
Syrup feeder
1. Train foragers from each hive to a feeder,
allow to dance, and count recruits to feeder
north
south
250m
250m
2. Repeat (1) but to opposite feeder
north
south
250m
250m
3. Repeat (1, 2) for 400m and 460m feeders
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Recruitment to Syrup Feeders
No. of recruits 151 19 15 8 18
2
100
Oriented light Diffuse light
recruits to feeder
50
0
N hive S Trial 1 250m
N hive S Trial 2 400m
N hive S Trial 3 460m
On average, one third as many recruits came to
the feeders visited by foragers from the diffuse
light hives as the oriented light hives. This
indicates that waggle dances in diffuse light
hives were not working.
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Results Hive Weight Changes
Oriented light
Diffuse light
300g
Change in hive weight over 11-day period
-300g
Summer P 0.22
Autumn P 0.85
Winter P 0.0005
In all three seasons the hives with oriented
light do better than those with diffuse light.
But this difference is only significant in
winter. Over all three seasons the difference is
significant.
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Analysis of Variance of Change in Hive Weight
Source of Variation d.f. Probability Season
(summer, autumn, winter) 2 0.0001 highly
significant 11-day period within
season 16 0.0001 highly significant Colony
pair 1 0.0693 not significant Colony
within pair 2 0.268 not significant Light
treatment (diffuse, oriented) 1 0.0038 highly
significant Season x light treatment 2 0.0319
significant Residual 51 Anova shows that
season and period both have an effect. This is
not surprising. Some seasons are better than
others and some 11 day periods are better than
others. Light treatment also had a significant
effect, with colonies subjected to oriented light
gaining more weight. There was also a significant
interaction of season and light treatment meaning
that the effect of the light treatment varied
among seasons. Overall, this means that dances
are useful, and are more useful in some seasons
that others.
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Social Foraging in Birds
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Social Foraging in Birds Ospreys
In some coastal areas, ospreys (large fish-eating
hawks) form loose gregarious nesting colonies.
Shoaling fish are a particularly good prey item.
Do ospreys watch colony mates to find fish?
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Getting Help from Companions Ospreys
Departing ospreys leave in all directions (A).
But if an osprey returns with a fish, others may
leave in that direction (B). Information is not
deliberately communicated, and the forager
probably receives little or no benefit (and maybe
even a cost) for informing other birds where fish
are.
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Getting Help from Companions Ospreys
Informed birds find fish more quickly than naïve
birds. If this were not the case, then there
would be no benefit in receiving information.
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Getting No Help from Companions Swallows
Barn swallows nest in colonial aggregations If
they gain information on food location from
successful colony mates then unsuccessful
foragers should tend to follow a successful
departing neighbour. But they do not (see
slide). In addition, successful foragers were no
more likely to be followed than unsuccessful ones
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Getting No Help from Companions Swallows
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Group Hunting
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Army Ant Colony
Small ants can capture larger prey by working
together.
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Group Hunting in Female Lions
African lion females live in groups and hunt
together.
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Group Hunting
Social carnivore mammals can capture prey
weighing between 6-12 times as much as any one
adult hunter. Solitary carnivores typically hunt
much smaller prey species This is a common
pattern across carnivores in unrelated taxa
(hyenas, cats, dogs). Also, divergence in some
groups between related species The comparative
method indicates that group hunting is a
behavioural adaptation for hunting larger prey.
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Group Hunting
Small groups do not disband during times of prey
scarcity
Singletons often eat as much or more than group
hunters. So why group?
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Group Hunting
Why continue to hunt in groups? Creel and Creel
pointed out that benefit in terms of meat gained
is only half the equation. There are also costs
in terms of energy expended chasing prey etc.
Are group hunters actually maximizing the
difference between energy gained and energy
expended?? They studied this in African wild
dogs.
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African Wild Dogs
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African Wild Dogs
The Creels measured weight of meat gained by wild
dogs in packs of between 3 and 20. Measured costs
in terms of distance run during hunting. They
calculated1) meat gained per dog per day 2)
meat gained per dog per day minus energetic cost
of hunting.
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Selecting What to Eat Costs Benefits
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Selecting What to Eat Costs Benefits
Optimality logic Selection will favour animals
that forage more efficiently. Costs and
benefits of different behaviours e.g.,
maximising food intake per unit time When a
hypothesis based on cost benefit logic is found
to be incorrect this can lead to further
insights, such as an additional factor that
affects foraging efficiency. In the study of
oystercatchers feeding on mussels, it was found
that some large mussels were impossible to open.
Optimality modelling To determine the best
course of action for an animal e.g., maximising
food intake per unit time Frequently graphical
models, simple underlying mathematics
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Oystercatchers Choosing Mussels
Predictions of two cost benefit models
The oystercatchers do better by selecting larger
mussels (Model A) as these yield more food. But
when only mussels that can successfully be opened
are considered, the optimum size of mussel is not
as large as possible, but c. 50mm. This matches
better with observations, which show that birds
do not select both small mussels, and the very
largest.
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Whelk Choice by Northwestern Crows

• Observations
• Northwestern (USA) crows drop whelks on rocks to
  break them open.
• Always select large whelks, drop them from c.
  5m.
• Keep dropping a whelk until it breaks.
• Data. Dropping whelks from a tower.

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What Would You Predict if...
What differences from the observed behaviour
would you predict if 1. Some whelks are
impossible to break open 2. Robber birds are
present which steal dropped whelks 3. Small
whelks are much easier to break open than large
whelks 4. Only small whelks are present
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Social Foraging Pharaohs Ant Trails
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Trail Re-establishment
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Antennae Down
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Antennae Up
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Trail Re-establishment