Lecture 5, Part 4- Foraging (what to eat)- Rule of thumb. Flashcards
What do Northwest crows do?
When foraging at the shoreline, what are they presented with?
What do they need to do?
Fly up- drop shellfish- on rocks- breaks shell- eat it.
Many things to eat like clams.
Decide which to focus on as they invest a lot of effort in it.
Continuation from Northwest crows:
What is the effort?
Why?
What are three decisions that crows have to make?
What do they use to make these decisions?
Flying high + dropping it hard enough to break it.
Uses energy- more than they would get from eating it (if its hard to break).
1) Which type to eat.
2) How high to fly before dropping it.
3) How many times they are going to keep trying if it does not break the first time.
Rules of thumb.
Classic study on crows:
Who was this and when?
What three things did crows do?
If you assume crows are behaving in an optimal way, what can you do?
Zach (1970s).
1) Only selected large whelks (3.5-4.4 cm long).
2) Flew up 5 metres before dropping.
3) Tried every whelk until it broke, even if it took many flights.
Make predictions.
Continuation from the classic study on crows by Zach:
What are the three predictions that Zach made?
1) Large whelks- more likely to break- after dropping it from 5 metres.
2) Drops- less than 5 metres- less breakage- drops more than 5- no difference (would have flown higher if it was easier).
3) Probability of breakage- should be independent (or increase with)- number of previous drops.
Continuation from the classic study on crows by Zach:
What did the researchers do?
What did they find? 2 things.
Artificial drops- dropped small, medium and large whelks- at different heights.
1) Large whelks break more easily than medium and small.
2) Not worth going higher than 5 metres- no extra benefit.
Continuation from the classic study on crows by Zach:
What provides an objective measure of how much energy it takes to drop them?
What are crows doing?
What did Zach also do?
What did the calculations from the medium ones show?
When do they waste more energy?
What is their rule of thumb?
Height + number of drops.
Optimal solution- focusing on large whelks + dropping them 5 metres.
Calculations- saw large whelks made a profit.
Making a loss.
Flying up + dropping- small + medium ones.
Biggest is the best.
Continuation from the classic study on crows by Zach:
Which is better; large whelks or small clams?
What is better than medium whelks and how?
If crows were more clever, what would they have known?
Small clams- have better probability.
Large whelks- heavier- longer to get- but more calories.
Small clams- energy per second.
Clams- more energy efficient- than whelks- are fooled by size.
When does the rule of thumb lead to an optimal outcome?
When does the rule of thumb not lead to an optimal outcome?
When does the rule of thumb they use work best for them?
When choosing different size whelks.
Not when choosing whelks or clams.
Most contexts.
When animals are highly selective, what increases?
When they are not selective, what decreases?
Do individual animals make this decision themselves?
What can being highly selective also be called?
What can not being selective also be called?
How is whether or not a species is specialist or generalist decided?
What does being a generalist mean?
Search time.
Profitability- will spend more time ingesting things that are not actually profitable.
No.
Specialists.
Generalists.
Over evolutionary time.
You need to learn what is good to eat.
Prey selection in pied wagtails:
Give an example of a bird.
What do they eat?
What do they have a choice to focus on?
What is the common fly size and what size do they eat?
What size of fly do the maximum calories per second come from?
Wagtail birds.
Flies- vary in size.
Any size fly + can eat whatever is around.
8mm- they eat a little less than this- are being selective.
7mm- they eat this- they are behaving in a sensible fashion.
