| 1. |
- Brodin, Anders, et al.
(författare)
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Memory and brain in food-storing birds: Space oddities or adaptive specializations?
- 2008
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Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 114:7, s. 633-645
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Forskningsöversikt (refereegranskat)abstract
- Scatterhoarding birds that cache food items have become an important model system for the study of spatial memory and its correlates in the brain. In particular, it has been suggested that through adaptive specialization, species that cache food have better spatial memory and a relatively larger hippocampus than their non-caching relatives. Critics of this approach, dubbed neuroecology, maintain that neither of these hypotheses has been confirmed. Here, we review the evidence pertaining to a correlation between food-storing capability and the relative volume of the hippocampus. Hippocampal volume has been related to food-storing behaviour in comparisons between species, within species, or within individuals, but the evidence is not consistent. There are several possible reasons for this inconsistency, including: (1) food-hoarding birds may not always use memory for retrieval, (2) there may be systematic differences between data from North American and Eurasian species that affect the analysis, and (3) sample sizes have in many cases been too small. In addition, both the independent variable (degree of food-hoarding specialization) and the dependent variable (relative volume of the hippocampus) are not clearly and consistently defined. Alternatively, it is possible that the neuroecological hypothesis is false. Systematic empirical research is necessary to determine whether or not food-storing birds have evolved adaptive specializations in brain and cognition.
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| 2. |
- Bäckman, Johan, et al.
(författare)
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The influence of fat stores on magnetic orientation in day-migrating Chaffinch, Fringilla coelebs
- 1997
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Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 103:3, s. 247-256
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Tidskriftsartikel (refereegranskat)abstract
- Earlier experimental studies have demonstrated the ability of day-migrating birds to perform migration under overcast skies, thereby indicating use of cues other than solar. The orientation behaviour of the chaffinch, a diurnal migrant, was investigated in orientation cage experiments during the autumn migration period. The aim of our experiments was to examine the relationship between different orientation cues and the influence of body condition on directional choices. We obtained the following results: 1. Chaffinches displayed a bimodal distribution of headings along a SW-NE axis when tested in the local geomagnetic field (controls); 2. When the geomagnetic field was experimentally deflected 90° counterclockwise, the chaffinches responded by changing their preferred axial orientation to SE-NW; and 3. The predictive power of stored fat reserves became evident when both the control and experimental samples were subdivided into fat and lean individuals. The majority of fat controls orientated towards a seasonally appropriate SW direction, whereas lean controls chose mean directions towards the NE. Experimentals followed the same pattern, but with the expected deflection, i.e. fat birds selected SE headings and lean individuals chose a NW mean direction.
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| 3. |
- Håkansson, P, et al.
(författare)
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Communal spawning in the common frog Rana temporaria - Egg temperature and predation consequences
- 2004
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Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 110:9, s. 665-680
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Tidskriftsartikel (refereegranskat)abstract
- Females of the common frog, Rana temporaria, spawn synchronously at communal breeding sites, forming a communal egg mass of individual spawn clumps. A total of four spawning sites were studied. In the centre of the communal egg mass, daily maximum temperature was higher and minimum temperature lower than further out. Spawn clumps in the centre of the communal egg mass developed faster than single spawn clumps. In the centre of the egg masses, some spawn clumps suffered almost total egg mortality. This was probably the consequence of a cold spell with sub-zero temperatures in combination with a tendency for low minimum temperatures in the centre. In a laboratory study, worm leeches, Erpobdella spp., fed readily on eggs of common frog, while horse leeches, Haemopis sanguisuga, hardly ate any eggs. At the spawning sites, most worm leeches were found in single spawn clumps, far from the communal egg mass. Females which spawned late, when most of the spawning was over, preferred to spawn in the centre of the communal egg mass. This suggests that there is a net advantage for eggs in spawn clumps laid in the centre.
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| 4. |
- Nilsson, Anders, et al.
(författare)
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Environmental Conditions and Intraspecific Interference: Unexpected Effects of Turbidity on Pike (Esox lucius) Foraging
- 2009
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Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 115:1, s. 33-38
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Tidskriftsartikel (refereegranskat)abstract
- Interference among predators decreases per capita foraging rates and has implications for both community dynamics and top-down trophic processes. Interference originates from behavioural interactions among foragers, and these behaviours could be affected by environmental conditions. In experiments on pike foraging alone or among conspecifics in different levels of water turbidity, we expected high turbidity to decrease the perceived risk of intraspecific interactions among pike, and thereby decrease the strength of interference, as turbidity would decrease the visual contact between individuals and act as a refuge from behavioural interactions. The results show that this is not the case, but suggest that interference is induced instead of reduced in high turbidity. Per capita foraging rates do not differ between pike foraging alone or in groups in our clear and moderately turbid treatments, indicating no effect of interference. As high turbidity enhances prey consumption for pike individuals foraging alone, but does not have this effect for pike in groups, high turbidity induces the relative interference effect. We suggest that future evaluations of the stabilizing effects of interference on community dynamics and its reduction of predation impact on top-down trophic cascades should consider potential unexpected effects of environmental conditions.
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| 5. |
- Nilsson, Jan-Åke
(författare)
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Establishment success of experimentally delayed juvenile marsh tits (Parus palustris)
- 1990
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Ingår i: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 85:1, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- By experimentally manipulating the time when young marsh tits, Parus palustris, could become established, I tested the influence of size, hatching date, social dominance in caged situations, and time of season on establishment success. Individuals that managed to become established were divided into two groups: those that became established in new territories and those that were found in the same territory as the one where they were caught. In no circumstances did size, hatching date or social dominance influence establishment success. The only factor tested that had a significant effect on establishment success, was when the juveniles were released; those that established themselves in new territories had been released earlier than unsuccessful ones. Thus, prior occupancy rather than hatching date per se is the factor determining establishment in new territories. Juveniles that became re‐established in their former territory had been released significantly later than those not becoming re‐established. As the season progresses, increasingly fewer unestablished juveniles are present to fill vacancies. Thus, late‐released juveniles stood a better chance of finding their flock position still vacant compared with juveniles released early, whose previous positions would already have been occupied by other juveniles.
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| 6. |
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| 7. |
- Andersson, Malte, 1941
(författare)
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Evolution of classical polyandry: Three steps to female emancipation
- 2005
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Ingår i: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 111:1, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- In classical polyandry, sex roles are reversed and a female reproduces with several males, each of whom raises his offspring with little or no help from her. This mating system occurs in some fishes and birds, and it is of great interest in relation to parental investment, sex role and sexual selection theory. The evolution of classical polyandry, however, is debated and not well understood. It is here suggested to generally take place in three main steps. (1) First evolves male care for eggs, for reasons that differ between fishes and birds. (2) Second, a female becomes able to lay more eggs than a male can accommodate. This can happen, for example, by evolution of male pregnancy or smaller body size, or by female production of more or larger eggs, made possible by larger female body size or more food. Polyandry in several taxa is associated with shift to a habitat rich in food during the breeding season, to novel specialised foraging methods, or to both. A favourable food situation may be crucial for evolution of classical polyandry. (3) In step three, females compete to lay two or more clutches in sequence for different males. Successful polyandrous females obtain more offspring, spreading traits that enhance success in competition over males. Step three may be most likely in species with small body size, for reasons of reproductive constraints and seasonality. Evolution of classical polyandry appears to have followed these steps in shorebirds, coucals and pipefishes, but the reasons why certain species differ from their close phylogenetic relatives in being polyandrous are far from clear. Behavioural and ecological studies of additional species, and detailed phylogenies of taxa with diverse mating systems including polyandry, are needed for testing these ideas.
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| 8. |
- Borg, Åsa A., et al.
(författare)
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Interactions Among Female Guppies (Poecilia reticulata) Affect Growth and Reproduction
- 2012
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Ingår i: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 118:8, s. 752-765
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Tidskriftsartikel (refereegranskat)abstract
- Competition among females over resources may have consequences for their resource budgets and thereby the resource allocation between growth and reproduction. In addition, the consequences of femalefemale interactions may differ for dominant and subordinate individuals, with the dominant ones being at an advantage. In this study, we investigated the consequences of femalefemale competition in guppies by manipulating the competitive environment of females. We found that large guppy females dominated smaller females and that interactions between females likely are costly because females exposed to competition grew less. These females compensated by growing at a higher rate when no longer subjected to competition. The higher growth rate might in turn be the cause of the reduced reproductive effort in the more competitive treatments. Furthermore, interactions were more costly for females when they were in the subordinate role than in the dominant role, because the reduction in growth and reproductive effort was highest in females exposed to larger competitors. Whether there was a differential allocation of resources into growth and reproduction depending on dominance status needs further investigation. However, in general, smaller females had a higher growth rate than larger females, independent of competitive level. We also found a negative relationship between reproduction and growth in all treatments, indicating a cost of reproduction.
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| 9. |
- Griesser, Michael, et al.
(författare)
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Influence of Winter Ranging Behaviour on the Social Organization of a Cooperatively Breeding Bird Species, The Apostlebird
- 2009
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Ingår i: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 115:9, s. 888-896
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Tidskriftsartikel (refereegranskat)abstract
- Most cooperative breeding bird species live in family groups that are formed through the prolonged association of offspring with their parents. Research into cooperative families has in particular investigated the balance between cooperation and conflict over reproductive decisions. As a consequence of this research focus, social interactions among group members outside the breeding season are rarely studied, despite the fact that they are likely to be crucial for social decisions. We investigated the social dynamics and ranging behaviour of the family group living cooperatively breeding apostlebird (Struthidea cinerea) outside the breeding season. Group size changed between, but not within, the seasons, being smaller during the breeding season than in the winter season. This change in group size was a consequence of breeding groups merging after breeding, then splitting again before the next breeding season. While breeding groups used small, non-overlapping home ranges (x = 113 ha) around the nesting site, during winter groups moved up to 1200 ha (x = 598 ha), and interacted frequently with up to four other winter groups. In particular large groups often joined together during winter and spent up to 50% of their time associating with other large winter groups. This apparent fission-fusion system facilitated the exchange of group members, offering the possibility to form new breeding coalitions and new groups. The results of this study suggest that behaviour outside the breeding season can be of considerable importance to the social dynamics of both families and cooperative breeding in such systems.
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| 10. |
- Johnsson, Jörgen I, 1959, et al.
(författare)
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Social transfer of predation risk information reduces food location ability in European minnows (Phoxinus phoxinus).
- 2007
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Ingår i: Ethology. - : Wiley. - 0179-1613 .- 1439-0310. ; 113:2, s. 166-173
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about how food location ability of animals is affected by social information of predation risk. This question was therefore addressed in an experimental study where naïve 'observer' European minnows (Phoxinus phoxinus) were allowed to search for food in a maze in the presence or absence of a predator (Salmo trutta). Observer minnows were accompanied by conspecific demonstrators which had previously been trained in the same maze either in the presence or absence of the predator. Observer minnows were most likely to locate food when the predator was absent both during their trial and during the pre-training of demonstrators. When demonstrators had been trained with predators, observer success in locating the food was halved, although they were never exposed to predation risk themselves. When observers were exposed to predation risk their probability of locating food was further reduced regardless of the experience of their demonstrators. Our results show that predation risk can affect the foraging ability of minnows both directly and indirectly through social information from conspecifics. We conclude that social information may influence and constrain individual behavioural decisions, especially in rapidly changing environments where private information is often insufficient.
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