| 1. |
- Cresswell, Will, et al.
(författare)
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Does an opportunistic predator preferentially attack nonvigilant prey?
- 2003
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 66:4, s. 643-648
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Tidskriftsartikel (refereegranskat)abstract
- The dilution effect as an antipredation behaviour is the main theoretical reason for grouping in animals and states that all individuals in a group have an equal risk of being predated if equally spaced from each other and the predator. Stalking predators, however, increase their chance of attack success by preferentially targeting nonvigilant individuals, potentially making relative vigilance rates in a group relatively important in determining predation compared with the dilution effect. Many predators, however, attack opportunistically without stalking, when targeting of nonvigilant individuals may be less likely, so that the dilution effect will then be a relatively more important antipredation reason for grouping. We tested whether an opportunistically hunting predator, the sparrowhawk, Accipiter nisus, preferentially attacked vigilant or feeding prey models presented in pairs. We found that sparrowhawks attacked vigilant and feeding mounts at similar frequencies. Our results suggest that individuals should prioritize maximizing group size or individual vigilance dependent on the type of predator from which they are at risk. When the most likely predator is a stalker, individuals should aim to have the highest vigilance levels in a group, and there may be relatively little selective advantage to being in the largest group. In contrast, if the most likely predator is an opportunist, then individuals should simply aim to be in the largest group and can also spend more time foraging without compromising predation risk. For most natural systems this will mean a trade-off between the two strategies dependent on the frequency of attack of each predator type.
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| 2. |
- Kaby, Ulrika, 1975-
(författare)
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Attacking predators and fleeing prey : detection, escape and targeting behaviour in birds
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to further our understanding of predator and prey behaviour and decision making in different attack situations. The thesis deals with escape strategies, predator detection ability and prey targeting behaviour. Thus the thesis includes several aspects of a predation event and it includes studies both on prey animals and predators. In the first paper we show that blue tits (Parus caeruleus), a small passerine bird, are highly flexible in their escape behaviour and adjust their escape to the detailed behaviour of an attacking predator. The predator’s attack height influenced the blue tits’ ascent angles whereas attack speed influenced the lateral course of the flight. These escape responses might reflect a turning gambit between prey and predator. To adjust escape behaviour might therefore be very important for survival. Our result from the second paper suggests that the evolution of flexible escape behaviour is influenced by habitat and life style. We found that open living bird species adjusted their escape behaviour to the behaviour of a predator to a higher degree than skulky, cover living bird species did. The third paper deals with how different aspects of foraging influence blue tits’ ability to detect predators and time till take-off. Detection ability in prey can heavily affect their likelihood to escape successfully. The body posture of the blue tits (head-up or head-down) did not affect their detection ability whereas their orientation did; detection was delayed when the attack came from behind. Foraging behaviour is often assumed to delay predator detection but we could not find any negative effect of an easy foraging task. A difficult task, on the other hand, severely delayed detection of the predator and time to take-off. In the last paper we investigate if sparrowhawks (Accipiter nisus) hunting opportunistically can discriminate between prey birds on the basis of vigilance state and preferentially target foraging birds for attack. The sparrowhawks showed no preference for foraging prey which is in contrast to predators which inspect their prey before attack. Thus our results suggest that predators may only have time to discriminate between individuals on the basis of vigilance state when stalking.
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| 3. |
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| 4. |
- Kaby, Ulrika, et al.
(författare)
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What limits predator detection in blue tits (Parus caeruleus) : posture, task or orientation
- 2003
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 54:6, s. 534-538
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Tidskriftsartikel (refereegranskat)abstract
- To detect threats and reduce predation risk prey animals need to be alert. Early predator detection and rapid anti-predatory action increase the likelihood of survival. We investigated how foraging affects predator detection and time to take-off in blue tits (Parus caeruleus) by subjecting them to a simulated raptor attack. To investigate the impact of body posture we compared birds feeding head-down with birds feeding head-up, but could not find any effect of posture on either time to detection or time to take-off. To investigate the impact of orientation we compared birds having their side towards the attacking predator with birds having their back towards it. Predator detection, but not time to take-off, was delayed when the back was oriented towards the predator. We also investigated the impact of foraging task by comparing birds that were either not foraging, foraging on chopped mealworms, or foraging on whole ones. Foraging on chopped mealworms did not delay detection compared to nonforaging showing that foraging does not always restrict vigilance. However, detection was delayed more than 150% when the birds were foraging on whole, live mealworms, which apparently demanded much attention and handling skill. Time to take-off was affected by foraging task in the same way as detection was. We show that when studying foraging and vigilance one must include the difficulty of the foraging task and prey orientation.
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| 5. |
- Kullberg, Cecilia, et al.
(författare)
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Impaired flight ability prior to egg laying : A cost of being a capital breeder
- 2005
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 19:1, s. 98-101
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Tidskriftsartikel (refereegranskat)abstract
- 1To investigate flight ability in captive Zebra Finches during reproduction we compared change in escape take-off ability and wing load of reproducing females with their mates and non-reproducing females when attacked by a model raptor. 2Initially females had 18% higher wing load than males. Non-reproducing females and females that had started egg-laying flew slower than males. Reproducing females reduced wing load during egg-laying and flew faster when the clutch was completed. Non-breeding females remained on high wing load and flow slower than breeding females that had completed their clutch. 3The increase in flight speed of breeding females was explained by a reduction in wing load during egg-laying. 4Zebra Finches use accumulated reserves to produce eggs and pay a cost in terms of reduced flight ability, but then regain flight performance when the clutch is laid, probably demonstrating a predation cost of capital breeding in birds.
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| 6. |
- Lind, Johan, et al.
(författare)
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Split-second escape decisions in blue tits (Parus caeruleus)
- 2002
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Ingår i: Die Naturwissenschaften. - : Springer Science and Business Media LLC. - 0028-1042 .- 1432-1904. ; 89:9, s. 420-423
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Tidskriftsartikel (refereegranskat)abstract
- Bird mortality is heavily affected by birds of prey. Under attack, take-off is crucial for survival and even minor mistakes in initial escape response can have devastating consequences. Birds may respond differently depending on the character of the predator's attack and these split-second decisions were studied using a model merlin (Falco columbarius) that attacked feeding blue tits (Parus caeruleus) from two different attack angles in two different speeds. When attacked from a low attack angle they took off more steeply than when attacked from a high angle. This is the first study to show that escape behaviour also depends on predator attack speed. The blue tits responded to a high-speed attack by dodging sideways more often than when attacked at a low speed. Escape speed was not significantly affected by the different treatments. Although they have only a split-second before escaping an attack, blue tits do adjust their escape strategy to the prevailing attack conditions.
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