1 / 24

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 stay or move on?. Currency: maximize rate of intake. Foraging Decisions.

nailah
Download Presentation

FORAGING (PART II)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related