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 stay or move on? Currency: maximize rate of intake

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

Fixed portion – 10 nuggets/day Variable portion – 5 or 20 nuggets/day WHICH IS THE BETTER OPTION?

“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

Caraco et al (1980’s – 1990’s) Juncos - Junco phaenotus Feeders Every visit OR NOTE: Same average reward Constant reward Variable reward

Caraco et al (1980’s – 1990’s) Juncos - Junco phaenotus Feeders Every visit OR Juncos behave as if they are risk adverse

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 = 3Average reward = 6

Caraco et al (1980’s – 1990’s) Juncos - Junco phaenotus OR When Reward constant = ½ Reward variable 50% of juncos chose the variable

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

A MODEL FOR THIS Survival Energy level at dusk (arbitrary units)

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) or 6 9 or 7 (ii) – take risk (i) – play it safe

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

FOOD STORAGE Imagine two strategies HoarderFreeloader Cost - high Benefit - high Cost - low Benefit - high AN ESS ONLY IF MEMORY IS INVOLVED

Willow tit Seeds labelled with 35 S Number with labelled feathers Given 35 S seeds Not given 35 S seeds

Optic chiasma

Time Visits Percentage Same eye Other eye Marsh tit

Clark’s nucracker Memory in Corvids Pinyon jay Mexican jay Western scrub jay High Low Reliance on stored food High Low Spatial memory

Hippocampal size Groups that don’t store foodGroups that store food

Hippocampal size Shorter daylength Milder winter

Cognition Western scrub jay Store nuts Store worms Retrieve PREFER NUTS PREFER WORMS

Cognition Western scrub jay Food delivered when lights come on Food delivered 2 hours after lights come on

Cognition – variety in the diet Western scrub jay Fed nuts Fed dog food

Feeding and vigilance

Heller & Milinski, 1979

Feeding and vigilance