FORAGING (PART II)

1. FORAGING (PART II)

2. 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

3. 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

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

5. “BETTER” depends on benefit of eating different numbers of nuggets If need 10 nuggets to survive – should use 5/20 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

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

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

8. Caraco et al (1980’s – 1990’s) Juncos - Junco phaenotus Second question: Is there a level of food at which juncos start to become risk prone? Add food to variable feeder < OR Reward = 3 Average reward = 6

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

10. Caraco et al (1980’s – 1990’s) Did experiment at 1 and 19ºC Feeders Adequate at 19ºC but not at 1ºC Constant reward Variable reward OR Option preferred at 1ºC

11. A MODEL FOR THIS 1 Survival 0 5 6 7 8 9 10 Energy level at dusk (arbitrary units)

12. 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: State (i) (ii) Best to choose 8 or 6 7 (ii) – take risk 6 8 9 or 7 (i) – play it safe 7

13. 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

14. FOOD STORAGE Imagine two strategies Hoarder Freeloader AN ESS ONLY IF MEMORY IS INVOLVED Cost - low Benefit - high Cost - high Benefit - high

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

16. Optic chiasma

17. Marsh tit Same eye Other eye Percentage Visits Time

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

19. Hippocampal size Groups that don’t store food Groups that store food

20. Hippocampal size Shorter daylength Milder winter

21. Cognition Western scrub jay Store nuts Store worms Retrieve PREFER WORMS 0 120 124 Store worms Store nuts Retrieve PREFER NUTS 120 124 0

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

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