Class Announcements. Extended Example: Bird Song Learning. White-crowned sparrows and Social Learning. White-crowned sparrows and Social Learning

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Class Announcements Section reading Paper for next week is up online. The paper is Sexual Selection, Temperature, and the Lion's Mane. Section reading must be done before coming to section.

1 Class Announcements Section reading Paper for next week is up online. The paper is Sexual Selection, Temperature, and the Lion's Mane. Section reading must be done before coming to section. Web recording of the class bioe140.xml Click on a file and use the following login: Username: bioe140 Password: R2v1ew Extended Example: Bird Song Learning 1. Example: Bird Song Learning (Peter Marler) 2. White-crowned Sparrows different regional dialects (Marin and Berkeley) 3. Several possibilities for difference in song a. Genetic differentiation b. Is it cultural? Is song more like a meme? Test 1 1. Took eggs from both populations and raised them in lab (no social influences!) 2.At ~50 days young males made twittering song, only vaguely like the adult s song. 3.As they grew up, they kept singing but never developed the full song. 4.This shows there has to be a social component. Test 2 1. Reared birds with the tape recorded song of either Marin or Berkeley (randomized) 2.These bird sang whatever song they were exposed to perfectly 3.Differences in dialect was not genetic, but instead cultural/memetic.

2 Test 3 1.Took young WC sparrows and played Song Sparrow song. (Song Sparrow is a different, yet closely related, species to WC sparrow) 2.Young birds developed an aberrant song that resembled the song of birds that had not heard a song. 3. Even though highly memetic, there is a genetic component that constrains the songs they can learn. 4. If played both a Song Sparrow song and a White-crowned Sparrow song, they always chose to learn species-specific song (their own species song)! Test 4 1. Exposed bird to a song during its critical period (10-50 days of age), then deafened it. 2.Deafened birds could not develop the proper song. 3.At 150 days, males produce a subsong and try to match their own vocal output to their memory. They needed to hear themselves sing. Summary 1. Regional dialects are cultural and plastic. 2.Learning is needed: needed to learn song from other birds; needed to learn how the song sounds as it was practiced. 3.Learning the species specific song is canalized (probably due to natural selection). Economic Decisions and the Individual How much food to carry? Which prey items are preferred? Starvation and Predation risks Tradeoffs Cognitive abilities to forage 8

3 Optimality Models 1. Usually based on trade-off between costs and benefits of behavior a. Maximize benefits, minimize costs (B-C) 2. Test hypotheses by experimentally altering balance of trade-off or compare species where balances differ 3. Most commonly used for foraging a. But also for other behaviors where costs and benefits quantifiable How best to forage for food? 1. Foraging is costly in time, energy, and exposure to predators. Want to optimize it. 2. Problem: Resources typically distributed unevenly in habitat. 3. Problem: Need to balance traveling and searching time with how much food can be carried. 4. Marginal Value Theorem (Charnov 1976): model in which animals try to maximize rate of energy gain a. Marginal value : value of taking one more unit of resource in patch Modeling Foraging 1. Foraging typically represented by diminishing returns a. Food runs out or prey start to hide. 2. Loading curve models energy gain vs. time. 3. Tangent=slope that maximizes food delivery Modeling Foraging 1. Changing the travel time changes the optimal number of prey to bring back. 2. Can use these models to generate explicit predictions about foraging.

Foraging problem: How much to carry? Starlings 1. Feed young Tipula fly larvae called leatherjackets. 2. Foraging is energetically costly. Up to 400 round trips per DAY! 3.

Empirical evidence: Kacelnik 1984 2. Trained starling parents to collect mealworms from feeders 3. Mealworms dispensed at increasing intervals.

4 Foraging problem: How much to carry? Starlings 1. Feed young Tipula fly larvae called leatherjackets. 2. Foraging is energetically costly. Up to 400 round trips per DAY! 3. Problem: How many larvae to carry for each trip? a. As mouth fills up, foraging becomes less efficient. b. However, not efficient to return to the nest with very little food. Starling Foraging 1. Empirical evidence: Kacelnik Trained starling parents to collect mealworms from feeders 3. Mealworms dispensed at increasing intervals. This allowed him to specify a loading curve of known shape. a. The actual searching time of a bird would be difficult to measure. 4. The birds would simply wait for the next worm to arrive until it eventually flew back to its nest 5. He varied the distance of the wooden tray from between 8 and 600 meters from the bird s nest to see how distance influenced how long the bird stayed 14 Starling Foraging 4. Starlings collected more mealworms when the foraging time increased, as predicted. 5. Starlings appear to maximize the net rate of food delivery. a. Understand the currency and constraints of their foraging. b. A model based on maximizing energetic efficiency was not predictive. 15 Foraging in Bees 1. Bees often return to the hive with less than the maximum load they could carry. 2. Bees don t appear to be limited by how much nectar they can hold in their crop. 3. They are limited by the weight of nectar, which add energetic costs to flight. 4. The more the bee loads up, the more nectar will be used as fuel before it gets home. 16

5 Foraging in Bees 1. Schmid-Hempel et al. (1985) trained bees to fly to artificial flowers, each with 0.6 mg of nectar. 2. He varied the distance between the flowers to manipulate the cost of carrying the crop load of nectar. 17 Foraging in Bees 3. Bees went home with smaller load when distance between flowers was greater. 4. Bees maximize the currency of energetic efficiency, not the net rate of energy delivery. e=energy gained/energy expended r=energy gained/time 18 Why opposite pattern for starlings and bees? 1. Maximizing net rate is generally a good currency. a. Strategy A: spend 1 kj, gain 9kJ, forage 1 hr b. Strategy B: spend 10 kj, gain 90kJ, forage 1 hr c. Both have efficiency = 9, but strategy B has 10x the net gain. 2. Energy efficiency may be particularly important if you have a fixed amount of fuel. 3. In the case of bees, this may be the lifetime capacity for expenditure of energy. 19 Why opposite pattern for starlings and bees? 1. Schmid-Hempel and Wolf (1988) manipulated energy expenditure by fixing different size weights onto bees 2. Bees that worked hardest lived shortest amount of time; lifetime reduced from 10.8 to 7.5 days 3. Bees contribute more nectar overall to colony by maximizing efficiency 20

Shore crabs (Carcinus maenas) can easily break into small mussels, but don t gain much food.

6 Prey Selection 1, Prey choice depends on energy value (E) and handling time (h). 2. Profitability (E/h) determines which prey to eat when multiple types (species or different size classes) are available 3. For example, does ELarge/hLarge > ESmall/hSmall? 21 Prey Selection 4. Shore crabs (Carcinus maenas) can easily break into small mussels, but don t gain much food. Very large mussels take so long to crack open that they are not profitable in terms of energy yield per unit breaking time. 5. Shore crabs prefer mussels with highest rate of energy return when given a choice of different sized mussels. 22 Predation risk 1. Foraging = short-term caloric gain; predation = permanent death a. Balance energy intake with need to remain vigilant 2. Can cause predictions based on optimality models to differ from observations 3. Shift to less-preferred food when predation risk for preferred habitats is high a. But condition not static. Even high predation-risk habitats can be preferred if pay-off is big enough 23 Predation risk 1. Milinski and Heller (1978) examined if predation risk influences choice of food intake in sticklebacks (Gastersteus aculeatus) 2. Hungry fish preferred high prey densities. However, when a model kingfisher was flown over the tank, the fish moved to low prey density. 3. Low prey density allows more time for vigilance 24

Predation risk 1. Predation risk can also be age/size specific 2. Gilliam (1982) tested habitat preference as bluegill sunfish (Lepomis macrochirus) grow 3.

7 Predation risk 1. Predation risk can also be age/size specific 2. Gilliam (1982) tested habitat preference as bluegill sunfish (Lepomis macrochirus) grow 3. With no predators, fish foraged on benthic inverts which gave highest rate of food intake compared to plankton 4. When predatory bass added to ponds smaller sunfish foraged in reeds where food intake reduced by 1/3 and growth rate by 27%. Larger sunfish were safe and continued to forage in the benthos. 5. Fish maximized chance of survival by adapting their foraging strategy with age Food storing 1. Many birds collect food in the autumn, which they then hide. The food is retrieved during the winter and spring. a. A single nutcracker is estimated to store seeds in separate hiding places. 2. This helps them deal with environmental variability. Stored food is similar to body fat. Both are stored during times of plenty and used in times of scarcity. 3. Food storing requires spatial memory to retrieve the food. a. Hippocampus is the part of the brain involved in spatial memory. 26 Food storing 4. Species that store food tend to have larger relative hippocampal volumes than species that do not store food. a. Light blue = average for families that do not store food. b. Dark blue = average for familes that do store food. 27 Food storing and the evolution of cognition 1. Mental abilities extend beyond spatial memory in some food storing birds. 2. Nicky Clayton and colleagues tested this with Western scrub jays (Aphelocoma californica). 3. Test1: Can the jays remember what kind of food stored, as well as when and where (i.e. can they remember specific events)? 4. Experiment: Jays were allowed to store either nuts or worms and then could store the other food after 120 hours. Food was retrieved 4 hours later. 28

8 Food storing and the evolution of cognition 5. Worms are preferred, but they go bad by 124 hours, whereas nuts do not. 6. Birds retrieved the worms if they were stored second but not if they were stored first. a. Would do this even if the food was removed from the hiding place, which eliminated any scent cues. 7. Thus, they can remember what, where, and when they hid food! 29 Food storing and the evolution of cognition 1. Test 2: Can scrub jays interpret the knowledge of another individual? Can they recognize potential thieves 2. When a bird was observed by others when storing food, it would later on in private move the food cache to a new location. 3. Birds more likely to move food when observed by a dominant individual than by their partner or subordinate 4. Individuals also more likely to move cache if they stole food from others Evolution of cognition 1. Test 3: Can Scrub jays plan for the future? a. Mental time travel : ability to project into the future, independent of current physiological conditions, and plan accordingly. 2. Experiment: Raby et al. (2007) placed birds overnight either in a compartment where they received food first thing in the morning or in a compartment where they had to wait 2 hours before receiving food 3. After training period, birds were allowed to obtain nuts from a central room and store them. They preferentially stored them in the room where they had to wait for food in the morning. 4. Birds could anticipate in which room they would be hungry if locked in overnight! 31 Optimality Models Limitations What to do when an animal doesn t behave optimally? Incorrect assumptions currency incomplete knowledge either by animal or by scientist 32

9 Summary 1. Optimality models are used to make quantitative, testable predictions about the choices an animal makes that maximize the benefits, while minimizing costs a. The currency for maximum benefit and the constraints will influence predictions 2. Foragers often face trade-offs in relation to foraging: predation and/or starvation risk, handling time, etc 3. Foraging is a very important part of life and may lead to the evolution of higher cognitive abilities.

Foraging. This week in Animal Behaviour. How do animals choose? Do animals choose their food?

Foraging. This week in Animal Behaviour. How do animals choose? Do animals choose their food? This week in Animal Behaviour Lecture 22: Cooperation Lecture 23: Foraging Lecture 24: TBA Text chapters 10-11 LAB: Project 2 proposal seminars Midterm 2 on Tuesday Nov. 8 Foraging 1. Models of foraging