Mark Elgar

Animal Behaviour

Correlation, experimentationand comparison

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Outline

How do researchers make discoveries about animal behaviour?Natural variation

Experiments

Comparisons between species

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Why do animals forage in groups?

3

Predator vigilanceProb

ability*of*

detec/on

*

Group*size*

Probability of predator detection increases with group size

4

Predator vigilanceScan

ning'

rate'

Group'size'

Rate of scanning declines with increasing group size

4

Predator vigilance

Use natural variation in flock size to measure differences in scanning rate

Flock size

Head

-jerk

rate

/min

0

5

10

15

20

25

2 4 6 8 10 13 18 23 28 33 50

5

Studies of group foraging

6

The dilution effect

Probability = 1

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The dilution effect

Probability = 1Probability = 1/2

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The dilution effect

Probability = 1Probability = 1/2Probability = 1/3

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The dilution effect

Probability = 1Probability = 1/2Probability = 1/3Probability = 1/10

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The dilution effect

Individuals may invest less in scanning when risk of predation is lower

Are individuals changing their scanning rate due to the Dilution Effect, the

detection of predators or both?

?

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Patchy distributions

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Experimental approaches

Feeder1

Feeder2

Feeder3

Feeder4

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Experimental approaches

7"6"5"4"3"2"1"0"0"

4"

8"

12"

16"

20"

Flock&size&

Scan

s&pe

r&min&"

Negative correlation between scanning rate and flock size

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Selfish Herd Effect

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Experimental approaches

Long

feeder

VS

Square feeder

Spotted turtle doveSpilopelia chinensis

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10#8#6#4#2#0#0.0#

0.1#

0.2#

0.3#

0.4#

0.5#

Flock#size#

Vigilance#

Square#Feeder#Narrow#Feeder#

Experimental approaches

Birds reduced scanning rate with increasing

group size

Scanning rate was also lower at the square

feeder

Results:

Spotted turtle doveSpilopelia chinensis

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Do all birds forage in groups?

Large group size may lower predation risk, but also means increased competition for foodPredicition:

Foraging in groups less common in populations or

species where predation risk is low or non-existent

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Comparative analyses

Comparison of island versus mainland species of birds

Island species typically have smaller flock sizes than mainland species

Island Mainland

Mean flock size

Maximum flock size

Smaller Larger

Smaller Larger

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Ways of studying behavior (relying on natural variation; field experiments; inter-specific comparative analyses

Summary

Experiments reveal that individuals can reduce the risk of predation by foraging in groups, although comparative analyses suggest that other factors may promote group foraging.

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Cita%onsSlide-1 _MG_2581(peacock(spider(Maratus(volans(by(Jurgen(O=o((h=p://www.flickr.com/photos/59431731@N05/5521738809/).((Reproduced(with(permission(from(Jurgen(O=o.

Slide-3a)("Bison(herd(R(Lake(Audy(R(Riding(Mountain(NaUonal(Park"((h=p://commons.wikimedia.org/wiki/File%3ABison_herd_R_Lake_Audy_R_Riding_Mountain_NaUonal_Park.JPG)(by(Norm(Andreiw((CC(BY(3.0),(via(Wikimedia(Commonsb)("Shorebirds(01"((h=p://commons.wikimedia.org/wiki/File%3AShorebirds_01.jpg)(by(Ingrid(Taylar((CC(BY(2.0),(via(Wikimedia(Commonsc)( "Starfish(orgy((SUchaster(australis)"((h=p://commons.wikimedia.org/wiki/File%3AStarfish_orgy_%28SUchaster_australis%29.jpg)(by("Avenue"((CC(BYRSA(3.0),(via(Wikimedia(Commonsd)("Cassiopea(jellyfish"((h=p://commons.wikimedia.org/wiki/File%3ACassiopea_jellyfish.jpg)(by(Jacopo(Werther([Public(domain],(via(Wikimedia(Commonse)!"Red Fish at Papahānaumokuākea Marine National Monument" (h=p://en.m.wikipedia.org/wiki/File:Red_Fish_at_Papah%C4%81naumoku%C4%81kea.jpg)(by(US(Fish(&(Wildlife(Service(R(Pacific(Region((CC(BY(2.0),(via(Wikimedia(Commonsf)( "Wildebeest(and(impala(drinking"((h=p://www.flickr.com/photos/dkeats/6037865141)(by(Derek(Keats((CC(BY(2.0)g)(“ladybirds(overwintering”((h=p://www.flickr.com/photos/94852245@N00/4057249053)(by(seier+seier((CC(BY(2.0)h)("Nasua(narica((foraging)"((h=p://commons.wikimedia.org/wiki/File%3ANasua_narica_%28foraging%29.jpg)(by(Hans(Hillewaert((CC(BYRSA(3.0),(via(Wikimedia(Commons

Slide-4Graph(by(Mark(Elgar

Slide-5Figure(2(from(Animal'Behaviour,(Volume(29.((Mark(A.(Elgar(&(Carla(P(Ca=erall,(Flocking(and(Predator(Suveillance(in(House(Sparrows:(Test(of(An(Hypothesis,(pages(868R872,(1981.((Reproduced(with(permission(from(Elsevier.

Slide-6---a)("Emperor(penguins"((h=p://en.wikipedia.org/wiki/File:Emperor_penguins.jpg)(by("NSF/Josh(Landis"([Public(domain],(via(Wikimedia(Commonsb)("DesertGrasslandWhiptailLizard(AspidoscelisUniparens56"((h=p://commons.wikimedia.org/wiki/File%3ADesertGrasslandWhiptailLizard_AspidoscelisUniparens56.jpg)(by("Ltshears"((CC(BYRSA(3.0),(via(Wikimedia(Commons((c)( "RUDDY(TURNSTONE(RUNNING(ALONG(SANIBEL(BEACH"((h=p://commons.wikimedia.org/wiki/File%3ARUDDY_TURNSTONE_RUNNING_ALONG_SANIBEL_BEACH.jpg)(by(Peter(Wallack((CC(BYRSA(3.0),(via(Wikimedia(Commonsd)("Suricata(surica=a(RAuckland(Zoo(RgroupR8a"((h=ps://commons.wikimedia.org/wiki/File%3ASuricata_surica=a_RAuckland_Zoo_RgroupR8a.jpg)(by(Ashleigh(Thompson((CC(BY(2.0),(via(Wikimedia(Commonse)("Nutmeg(Mannikin"((h=p://www.flickr.com/photos/pazzani/7504160732/)(by("Mike's(Birds"((CC(BYRSA(2.0)f)( "ghostRcrab_w725_h476"((h=p://www.publicRdomainRimage.com/faunaRanimalsRpublicRdomainRimagesRpictures/crabsRandRlobstersRpublicRdomainRimagesRpictures/ghostRcrab.jpg.html)(by(Harrison(George,(U.S(Fish(and(Wildlife(Service([Public(domain]

Slide-7-&-8-Birds(by(Milly(Formby(©(University(of(Melbourne

Slide-9a)(Birds(by(Milly(Formby(©(University(of(Melbourneb)(Green(Yellow(Cartoon(Bug(Insect((h=p://pixabay.com/en/greenRyellowRcartoonRbugRinsectR34375/)(by(Nemo([Public(Domain](via(pixabay

Slide-10Experimental(Approaches(Feeder(Diagram(by(Milly(Formby(©(University(of(Melbourne

Slide-11Graph(by(Mark(Elgar

Slide-13a)("The(Fence(Si=er"((h=p://www.flickr.com/photos/aussiegall/608251625/)(by(Louise(Docker((CC(BY(2.0)b)(‘Square(feeder(vs(long(feeder’(by(Milly(Formby(©(University(of(Melbourne(

Slide-14Flock(size(vs(Vigilance(graph(by(Mark(Elgar

Slide-16Data(sourced(from((Beauchamp,(G.)(Reduced(flocking(by(birds(on(islands(with(relaxed(predaUon.(Proceedings:'Biological'Sciences,(Vol(271.(No.(1543((2004),(pp.(1039(–(1042.((The(Royal(Society.

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