Behavioural Adaptations for Survival. BIOL 3100. Mobbing behaviour. When a predator is spotted, birds, like chickadees, will give a specific alarm call or mobbing call. When heard, all individuals present come in to investigate and attack the intruder (hawk, owl).
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Behavioural Adaptations for Survival
When played back chickadee mobbing calls and other chickadee vocalizations, significantly more birds approach the speaker and display mobbing behaviour during mobbing call playback
Thus, chickadee mobbing calls carry meaning for at least 10 other avian species
The different warnings help flock mates grasp the relative threat of the intruder
Flying owls, hawks and flacons provoke a high-pitched “seet” call
Perched predators evoke a loud “chickadee” call
Small raptors, like saw whet owls and American kestrels (which are the biggest threat) provoke more “dees” at the end of the call and elicit a larger response
Same behaviour is exhibited by gulls when a predator, such as a raptor (or researcher) is present
A student of Niko Tinbergen’s, Hans Kruuk, was interested in examining the ultimate causes of mobbing behaviour in black-headed Gulls
Question: Is mobbing an adaptive behaviour and a product of natural selection?
Hypothesis: Mobbing distracts certain predators, reducing the chance that they would find the mobbers’ offspring, boosting the fitness of mobbing parent gulls
So, if mobbing behaviour is adaptive, why don’t 100% of the parents mob predators 100% of the time? In other words, why doesn’t the mobbing phenotype “win out”
One approach to test whether a trait is adaptive is to take a cost-benefit approach in which different phenotypes are analyzed in terms of fitness costs and benefits
Benefit: Mobbing prevents offspring from getting eaten, predators forced to spend more time searching for prey
Costs: Time and energy expended, getting eaten yourself by the predator
California ground squirrels react to hunting rattlesnakes by gathering around it and shaking their tails vigorously to encourage it to depart before being physically attacked by the squirrels.
Also have a pretty cool adaptation we’ll talk about on Friday…
Species from different evolutionary lineages that live in similar environments and are subject to similar selective pressures may evolve similar traits through convergent evolution
In other words, different taxa may find the same solution to the same problem.
Though the squirrels do have some antivenom, there are costs to being bitten by a snake
Hypothesis: Squirrels should adjust behaviour based on the degree of threat.
Test: When rattles of different sized snakes were played back, the squirrels approached the big snake rattle sound more cautiously than the small snakes.
Observation: Butterflies aggregate in large, densely packed groups around mud puddles on tropic riverbanks, where they suck up minerals from the soil.
Hypothesis: Bigger groups are more likely to attract avian predators, but cost offset decreased chance that any one individual will be eaten
Test: Examine probability of capture in relation to group size
… in this case, the benefits of joining a larger groups substantially outweigh the costs
Is this the reason that mayflies all emerge at the same time so as to effectively lodge in your teeth while biking (or eaten by trout when they emerge from water)?
Test: Use nets to capture cast-off skins of mayflies, as well as dead female mayflies, which die naturally after laying their eggs, unless they’re eaten first…
Sweeny & Vannote
Anti-predator behaviour can also be exhibited through direct attacks on potential predators.
Have you ever stepped on a wasp nest?
Sawfly larvae cluster in balls of ~10 individuals where they feed on eucalyputus leaves, which contain resinous, toxic oils, which they store in special sacs and regurgitate onto attacking ants or birds.
Canyon treefrogsrely on camouflage for defense from predators, which means they need to pick the right rocks on which to cling tightly and be completely stationary.
Cryptic colouration depends on background selection. This Australian thorny devil is very well camouflaged when stationary against bark and debris, but highly conspicuous on a road.
The classic example of the peppered moth, Bistonbetularia
The classic example of the peppered moth, Bistonbetularia
In Great Britian and the US, the melanic form of the peppered moth was once extremely rare, but almost completely replaced the salt-and-pepper form from 1850-1950.
As industrial soot darkened the colour of forest tree trunks in urban areas the whitish moths became more conspicuous and were subsequently eaten, removing those genes
And yes, this experiment is still valid.
Observational study: examining the natural frequency of black and white morphs in response to changing conditions
Experimental study 1: Place moths on different trees (and on different locations on trees) and examine predation rates.
Moths of both types were less likely to be found and removed by birds on limb joints, but overall,
Orientation is also important. Catocalarelicta moths usually perch head-up with with whitish forewings over its body on white birch and other light-barked trees.
Is this behaviour adaptive?
If so, predators should overlook moths more often when they perch on their favorite substrate, in their preferred orientation.
Experimental study 2: Images of moths on different backgrounds and in different resting positions are shown to a captive blue jay, which is rewarded for detecting a moth.
Jays saw moths 10-20% less often when the moths were on light-coloured bark. Birds were especially likely to overlook moths when they were oriented head-up on birch bark.
Some species, like these grasshoppers (B) use large black and white patches to disrupt predators’ edge detectors, creating false edges. On the other hand, the black horse lubber grasshopper (C) emphasizes their outline to make them more conspicuous (aposomaticcolouration)
California ground squirrels chew on cast rattlesnake skins then lick their fur. Why?
When given captive rattlesnakes a chance to investigate filter paper, some of which had been rubbed on a squirrel then subsequently rubbed on snake skin, and other paper that just had been rubbed on a squirrel – the rattlesnake spent twice as much time inspecting pure squirrel-scented targets.