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- Benson, Scott A., et al.
(author)
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Graded-risk sensitivity in northern European mixed-species flocks of tit and nuthatch species
- 2022
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In: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 128:5, s. 437-442
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Journal article (peer-reviewed)abstract
- Avian species often use anti-predator calls such that the costs and benefits of vigilance are distributed within the group. Some species respond differentially to graded risk by attending to relevant predator cues, such as head orientation and gaze direction. One benefit of graded-risk sensitivity is fewer missed foraging opportunities. It is not known how the makeup of risk response behaviors in mixed-species flocks may relate to the relative nuclearity of each species in the flock. In the current study, predator models were presented to two nuclear and two satellite species of passerines that frequently occur in natural mixed flocks. Predator models either faced toward or away from a nearby stocked feeder to simulate high and low risk of predation, and calling and seed-taking rates of the present flock were recorded. The nuclear species, great tits (Parus major) and crested tits (Lophophanes cristatus), took more seeds when the predator faced away from the feeder than toward it. The satellite species, Eurasian nuthatches (Sitta europaea) and willow tits (Poecile montanus), did not show an effect of predator orientation. No species showed consistent differences in calling behavior relative to predator orientation, although insufficient calling data for great tits prevented analysis for this species. The results of this study suggest that one aspect of nuclearity in mixed-species flocks is a tendency for graded-risk sensitivity, or alternatively, that satellite species are more sensitive to mere predator presence rather than to predator orientation cues.
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| 3. |
- Hedlund, Johanna, et al.
(author)
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Increase in protandry over time in a long-distance migratory bird
- 2022
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 12:7
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Journal article (peer-reviewed)abstract
- Protandry is a widespread life-history phenomenon describing how males precede females at the site or state of reproduction. In migratory birds, protandry has an important influence on individual fitness, the migratory syndrome, and phenological response to climate change. Despite its significance, accurate analyses on the dynamics of protandry using data sets collected at the breeding site, are lacking. Basing our study on records collected during two time periods, 1979 to 1988 and 2006 to 2016, we aim to investigate protandry dynamics over 38 years in a breeding population of willow warblers (Phylloscopus trochilus). Change in the timing of arrival was analyzed in males and females, and protandry (number of days between male and female arrival) was investigated both at population level and within breeding pairs. Our results show advancement in the arrival time at the breeding site in both sexes, but male arrival has advanced to a greater extent, leading to an increase in protandry both at the population level and within breeding pairs. We did not observe any change in sex ratio that could explain the protandry increase, but pronounced temperature change has occurred and been reported in the breeding area and along the migratory route. Typically, natural selection opposes too early arrival in males, but given warmer springs, this counteracting force may be relaxing, enabling an increase in protandry. We discuss whether our results suggest that climate change has induced sex-specific effects, if these could be evolutionary and whether the timing of important life-history stages such as arrival at the breeding site may change at different rates in males and females following environmental shifts.
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| 4. |
- Kullberg, Cecilia, 1967-
(author)
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Behaviour under predation risk in birds
- 1998
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Doctoral thesis (other academic/artistic)abstract
- Predation is a major selective force in the evolution of both morphological and behavioural characters in animals. The flexibility in behavioural traits according to perceived predation risk has received much attention in recent years. Since resources often are limited, prey animals face a trade-off between the risk of predation and other energy demanding activities in life. This thesis investigates the effect of predation risk on some behavioural traits in birds. The two main topics under study are predation risk and niche use in the genus Parus, and mass-dependent predation risk in birds.In a field study investigating hunting behaviour in relation to prey choice in wild pygmy owls, Glaucidium passerinum, I found that when hunting for birds, owls used a hunting strategy attacking the birds with a height advantage from ambush. This observation suggests that birds foraging high in the tree and close to the trunk, sheltered by branches, face a lower predation risk than birds foraging further out and lower down in the tree. In a laboratory experiment with wild caught willow tits, Parus montanus, I investigated the use of foraging sites in the tree according to perceived predation risk. The tits adjusted foraging behaviour to the present predation risk by choosing more sheltered foraging sites after the presentation of a model raptor. Since the hunting strategy of pygmy owls lead to selective predation of birds foraging in the outer parts of branches, the pygmy owl might acts as a keystone predator enabling coexistence of tit species that are separated in their foraging niches. The coexistence of willow tits, crested tits, Parus cristatus, and coal tits, P. ater, could be a result of a two-way asymmetric interaction between species competing for food and predator safe foraging sites.Laboratory experiments investigating take-off ability in relation to diurnal body mass increase ((8%) in wintering willow tits and great tits, Parus major, showed no measurable effect on flight ability, indicating that the small energy reserves accumulated during a day in wintering tits do not increase predation risk as a consequence of reduced take-off ability. However in a similar experiment studying migratory fuel load (up to 59% of lean body mass) in blackcaps, Sylvia atricapilla, a reduction in both velocity and angle of ascent was found suggesting that the large fuel loads needed for migration place the birds at an increased risk of predation. The study of alarmed take-off flights in great tits further suggests that great tits adjust take-off strategy to the attack trajectory of an attacking raptor, indicating that the trade-off between velocity and angle of ascent during take-off is affected by the nature of the predator attack.
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| 5. |
- Sveider, Cecilia, 1974-
(author)
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Representationer av tal i bråkform : En studie om matematikundervisning på mellanstadiet
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Syfte med avhandlingen är att skapa förståelse för lärares undervisning om tal i bråkform på mellanstadiet. Avhandlingen består av två delstudier. I delstudie I studeras hur lärare och elever använder laborativa material för att representera tal i bråkform. Delstudie II fokuserar på hur lärare använder olika representationer för att representera tal i bråkform och hur dessa kopplas samman. I båda delstudierna studeras vad eleverna ges möjlighet att erfara om tal i bråkform. Totalt har 33 olika matematiklektioner videofilmats. Materialet har analyserats genom en växelverkan mellan empirin, variationsteorin och begrepp från tidigare forskning. Resultatet visar att när lärarna undervisar riktar de uppmärksamheten mot och varierar olika aspekter av ett lärandeobjekt, vilket innebär att eleverna ges olika möjligheter att erfara lärandeobjektet. En variation av hur lärarna handlar i undervisningssituationen som har betydelse för vad eleverna ges möjlighet att lära har uppmärksammats vad gäller olika sätt att synliggöra kunnandet. Tre mönster avseende på lärares handlande som framträtt är: (a) variation av innehållet, (b) användningen av representationer, dels utifrån vilka representationer som används, dels utifrån hur olika representationer kopplas samman och (c) val av exempel.
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