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FORAGING (PART II)

FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

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Page 1: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

FORAGING (PART II)

Page 2: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Foraging Decisions

Feeding holes(24/log)

-seeds placed in 0, 6, 12, and 24 holes

After a bird samples a log, how does it decide to stay or move on?

Currency: maximize rate of intake

Page 3: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Foraging Decisions

After a bird samples a log, how does it decide to stay or move on?

If 0 or 24 holes with seeds- - average of 1.7 ‘looks’

If 6 or 12 holes with seeds- Model predicts 3 or 6 ‘looks’ per log

Experiments – 3.5 and 6.3 ‘looks’ per log

Page 4: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Fixed portion – 10 nuggets/day

Variable portion – 5 or 20 nuggets/day

WHICH IS THE BETTER OPTION?

Page 5: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

“BETTER” depends on benefit of eating different numbers of nuggets

If need 10 nuggets to survive – should use 10 nugget option

If need >10 nuggets to survive – lose nothing by going to 5/20 option

Therefore – animals should be sensitive to both mean rate of return AND variability

Page 6: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Caraco et al (1980’s – 1990’s)

Juncos - Junco phaenotus

Feeders

Every visit

OR

NOTE: Same average reward

Constant reward

Variable reward

Page 7: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Caraco et al (1980’s – 1990’s)

Juncos - Junco phaenotus

Feeders

Every visit

OR

Juncos behave as if they are risk adverse

Page 8: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Caraco et al (1980’s – 1990’s)

Juncos - Junco phaenotus

OR

Second question: Is there a level of food at which juncos start to become risk prone?

Add food to variable feeder

<

Reward = 3 Average reward = 6

Page 9: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Caraco et al (1980’s – 1990’s)

Juncos - Junco phaenotus

OR

When Reward constant = ½ Reward variable

50% of juncos chose the variable

Page 10: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Caraco et al (1980’s – 1990’s)

Did experiment at 1 and 19ºC

Feeders

OR

Constant reward

Variable reward

Adequate at 19ºC but not at 1ºC

Option preferred at 1ºC

Page 11: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

A MODEL FOR THIS

1

0

5 6 78 9 10

Survival

Energy level at dusk (arbitrary units)

Page 12: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

A MODEL FOR THIS

Foraging options:

1) Provides 1 unit of energy with a probability of 1.0

2) Provides 2 units of energy with a probability of 0.5 and 0 units of energy with a probability of 0.5

Option chosen depends on current hunger state

Energy level if choosing:

Best to chooseState (i) (ii)

6

7

7

8

8 or 6

9 or 7

(ii) – take risk

(i) – play it safe

Page 13: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

FOOD STORAGE

Clark’s nutcracker- can store about 30,000 seeds in 2500 – 4000 locations

Paridae - can store between 100,000 and 500,000 seeds

Page 14: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

FOOD STORAGE

Imagine two strategies

Hoarder Freeloader

Cost - high

Benefit - high

Cost - low

Benefit - high

AN ESS ONLY IF MEMORY IS INVOLVED

Page 15: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Willow tit

Seeds labelled with 35S

Number with labelled feathers

Given 35S seeds

Not given 35S seeds

Page 16: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Optic chiasma

Page 17: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Time Visits

Per

cen

tage

Same eye

Other eye

Marsh tit

Page 18: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Clark’s nucracker

Memory in Corvids

Pinyon jay

Mexican jay

Western scrub jay

High

Low

Reliance on stored food

High

Low

Spatial memory

Page 19: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Hippocampal size

Groups that don’t store food Groups that store food

Page 20: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Hippocampal size

Shorter daylength

Milder winter

Page 21: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Cognition

Western scrub jay

Store nuts

Store nuts

Store worms

Store worms

Retrieve

Retrieve

0

0

120

120

124

124

PREFER NUTS

PREFER WORMS

Page 22: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Cognition

Western scrub jay

Food delivered when lights come

on

Food delivered 2 hours after lights

come on

Page 23: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Cognition – variety in the diet

Western scrub jay

Fed nuts Fed dog food

Page 24: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Feeding and vigilance

Page 25: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Feeding and vigilance

Heller & Milinski, 1979

Page 26: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to

Feeding and vigilance

Page 27: FORAGING (PART II). Foraging Decisions Feeding holes (24/log) -seeds placed in 0, 6, 12, and 24 holes After a bird samples a log, how does it decide to