In Lorenz's ‘psychohydraulic model’, behaviour is regulated by performance: the motivation to perform a behaviour builds up with time and can be reduced only by performance itself. However, a ...convincing example of Lorenzian regulation has been lacking. We studied dustbathing in featherless and feathered chicks, Gallus gallus domesticus, the latter trained to dustbathe on glass with sand underneath. In both cases the function, that is, plumage cleaning, was eliminated. In both featherless and feathered chicks dustbathing increased with time since the last performance as found in normal dustbathing, and there was a compensatory adjustment when the amount of previous dustbathing was artificially reduced. We suggest that the amount of dustbathing performed at any one time may be controlled by the cooperative action of a deprivation or timer mechanism and a counter mechanism. The timer mechanism responds to the time since the last performance, whereas the counter mechanism records the number of elements during that last dustbathing. Alternatively, there may be a single mechanism that continually records the deficit in the amount of dustbathing performed. Lorenz's model may be valid not only for dustbathing in fowl but also for other comfort behaviours. Our results suggest the existence of behavioural needs that can be satisfied only by performance.
Yields in pound nets are in particular damaged or reduced by cormorant Phalacrocorax carbo predation. In this study we examined the effect on predation in pound nets by mounting barrel nets ...vertically under the water in the pot in order to obstruct cormorants during their hunt. To keep control of the content of fish we used an experimental pot with a closed throat. The pot was stocked repeatedly with rainbow trout Oncorhyncus mykiss and its content of fish was thereby maintained at between 10 and 100 individuals during all periods of data collection. Video recordings, both above and under water, were carried out during May - August 1995 under various experimental conditions. We tested five different barrel net arrangements including a control situation without barrel net. Two bird categories were defined a posteriori: those that caught one or more fish during their visit to the pot (successful birds) and those that failed to catch a fish (unsuccessful birds). Successful and unsuccessful birds differed in a number of ways. Successful cormorants stayed longer in the pot, performed more dives, and spent more time diving and shorter time on the surface. When barrel nets were present, fewer cormorants of both categories visited the pot. Furthermore, the barrel nets affected successful birds by increasing the number of dives required to catch their first fish, reduced the time that both successful and unsuccessful birds remained in the pot, and reduced the number of dives performed by unsuccessful birds. Therefore, it seems that barrel nets may have a potential as a predation reducing device in pound net fishery. Introducing the use of barrel nets in pound net fisheries may force cormorants to hunt in free waters, possibly with reduced foraging success. This may eventually lead to a reduction in the cormorant population which will make it better fit the natural carrying capacity of the environment.
Many reef fish have strong microhabitat preferences when they settle to the juvenile population, and choices at this time may influence fish survival. This is exemplified in anemonefishes (Family: ...Pomacentridae) that exhibit obligate symbiotic relationships with a restricted range of sea anemone species. This study examined how juvenile anemonefish Amphiprion melanopus select their host, and whether recognition and selection are mediated by an imprinting-like mechanism. Specifically, we experimentally examined the host-selection made by A. melanopus that had been reared under constant conditions, but whose embryos had received 1 of 3 treatments: (1) in contact with a known natural host sea anemone, Entacmaea quadricolor; (2) in contact with the sea anemone Heteractis malu, which is not a host for A. melanopus in nature, but is a host for anemonefish of other species; and (3) without a sea anemone (or chemical cues released from sea anemones) at any life stage. Our study shows that olfaction, not vision, is used by juvenile A. melanopus to recognize host anemones. Furthermore, the choice of a settlement site for juvenile A. melanopus is strongly influenced by events that occur early in development, prior to the dispersal of larvae from their natal site. We suggest that juvenile A. melanopus possess an innate preference for E. quadricolor, a preference that is enhanced by imprinting. Interestingly, it was not possible to imprint A. melanopus larvae to the non-host sea anemone H. malu, which suggests that anemonefish host-imprinting may be rather restricted.
Livestock grazing is common management practice in wet grasslands. However, knowledge of its effects on small mammals is limited. We studied the influence of grazing intensity on small mammals in ...general and field voles
Microtus agrestis in particular in two Danish wet meadows, 1998–2000. Generally, grazing livestock had a negative effect on the peak biomass of small mammals, and the negative effect increased with grazing intensity, irrespective of whether pens were grazed by cattle or by sheep. More detailed analyses, however, revealed that an intermediate grazing intensity (approximately 400
kg
ha
−1 as maximum livestock biomass) actually seemed to benefit small mammals. This grazing intensity generally held small mammal biomasses and field vole population sizes that were similar to or larger than those on the ungrazed control, and markedly larger than those on the more heavily grazed pens. Additionally, field voles in the intermediate grazing intensity had more foetuses. Though a number of parameters may contribute to the observed patterns, we suggest that these primarily are caused by the livestock removing vegetation cover, thereby influencing the number and size of patches with high, dense vegetation in the vicinity of grass that is rejuvenated by grazing.
Die Viehbeweidung ist eine verbreitete Wirtschaftsform auf nassen Weiden. Dennoch ist die Kenntnis ihrer Auswirkung auf Kleinsäuger begrenzt. Wir untersuchten den Einfluss der Beweidungsintensität auf Kleinsäuger im Allgemeinen und Wühlmäuse
Microtus agrestis im Besonderen auf zwei dänischen nassen Weiden von 1998 bis 2000. Weidevieh hatte generell einen negativen Effekt auf die Spitzenbiomasse der Kleinsäuger und der negative Effekt nahm mit der Beweidungsintensität zu, unabhängig davon ob die Verschläge von Schafen oder Rindern beweidet wurden. Eine detailliertere Analyse ließ jedoch erkennen, dass eine mittlere Beweidungsintensität (ungefähr 400
kg pro Hektar als maximale Viehbiomasse) anscheinend Kleinsäuger fördert. Diese Beweidungsintensität hatte eine Biomasse kleiner Säuger und eine Wühlmauspopulationsgröße zur Folge, die vergleichbar oder größer als die der unbeweideten Kontrollen und wesentlich größer als die der viel stärker beweideten Verschläge war. Darüber hinaus hatten die Wühlmäuse bei der mittleren Beweidungsintensität mehr Foeten. Obwohl eine Anzahl von Parametern zu den beobachteten Mustern beitragen kann, vermuten wir, dass sie vor allem dadurch verursacht werden, dass Vieh die Vegetationsdecke entfernt und dadurch die Anzahl und Größe der Flecken beeinflusst, die hohe und dichte Vegetation aufweisen und in Nachbarschaft zu Gras liegen, das durch die Beweidung verjüngt wird.
Patch use under predation risk often results in a change of feeding behaviour in the prey animals. However, such changes only appear if the animals are able to assess under which predation pressure ...they live. We investigated patch use of Mastomys natalensis under different conditions of avian predation pressure. In replicated maize field plots in Morogoro, Tanzania, avian predators were allowed under natural conditions (control), attracted with perches and nest boxes or kept out with nets. During four one-week periods in late 1999, we measured rodent feeding decisions with the giving-up density (GUD) method. Trays with known amounts of millet seeds in sand were placed in pairs, one of them under a cover, the other one in the open. M. natalensis mice were expected to give up sooner in the open trays than in those with cover. We hypothesised that M. natalensis mice could assess the ambient predation pressure leading to larger difference in GUD between covered and non-covered trays in the plots where predators were attracted. We also made video recordings of the rodent activity at a pair of trays in each treatment. The GUD-values were significantly lower for the covered trays but predation pressure did not affect this difference. The video observations showed that in the control and netted plots the animals visited trays equally frequently regardless of the cover, while the visits in the predator-attracted plots occurred significantly more often in the covered trays. We conclude that M. natalensis can assess the ambient predation pressure and adapt its behaviour at a feeding patch. However, the variation in predation pressure in our experiment was not obvious from the GUD. Moreover, we found a strong relation between rodent density and GUD, which may mask variations in perceived predation pressure. Similar GUD values may be reached in different ways and we present models to investigate whether animals' decision to forage at a food patch is only affected by the seed density at that patch, not by that at a neighbour patch.
Wild bank voles (Clethrionomys glareolus) may develop diabetes in laboratory captivity. The aim of this study was to test whether bank voles develop type 1 diabetes in association with Ljungan virus. ...Two groups of bank voles were analyzed for diabetes, pancreas histology, autoantibodies to glutamic acid decarboxylase (GAD65), IA-2, and insulin by standardized radioligand-binding assays as well as antibodies to in vitro transcribed and translated Ljungan virus antigens. Group A represented 101 trapped bank voles, which were screened for diabetes when euthanized within 24 hours of capture. Group B represented 67 bank voles, which were trapped and kept in the laboratory for 1 month before being euthanized. Group A bank voles did not have diabetes. Bank voles in group B (22/67; 33%) developed diabetes due to specific lysis of pancreatic islet beta cells. Compared to nondiabetic group B bank voles, diabetic animals had increased levels of GAD65 (P < .0001), IA-2 (P < .0001), and insulin (P = .03) autoantibodies. Affected islets stained positive for Ljungan virus, a novel picorna virus isolated from bank voles. Ljungan virus inoculation of nondiabetic wild bank voles induced beta-cell lysis. Compared to group A bank voles, Ljungan virus antibodies were increased in both nondiabetic (P < .0001) and diabetic (P = .0015) group B bank voles. Levels of Ljungan virus antibodies were also increased in young age at onset of newly diagnosed type 1 diabetes in children (P < .01). These findings support the hypothesis that the development of type 1 diabetes in captured wild bank voles is associated with Ljungan virus. It is speculated that bank voles may have a possible zoonotic role as a reservoir and vector for virus that may contribute to the incidence of type 1 diabetes in humans.
Wild bank voles (Clethrionomys glareolus) kept in the laboratory under barren housing conditions develop high incidences of type 1 diabetes mellitus due to beta cell-specific lysis in association ...with the appearance of GAD65, IA-2, and insulin autoantibodies. Wild-caught and immediately analyzed voles show no histological signs of diabetes, and the disease may therefore be induced by circumstances related to the housing of the animals in captivity. We tested the possibility that postnatal stress by either maternal separation or water immersion at different intervals would induce diabetes in adult bank voles. We found that low-frequent stress during the first 21 days of life increases, whereas high-frequent stress markedly reduces, the incidence of type 1 diabetes in adulthood. These results differentiate the role of early-experienced stress on subsequent type 1 diabetes development and emphasize that the bank vole may serve as a useful new animal model for the disease.
Wild bank voles ( Clethrionomys glareolus ) may develop diabetes in laboratory captivity. The aim of this study was to test whether bank voles develop type 1 diabetes in association with Ljungan ...virus. Two groups of bank voles were analyzed for diabetes, pancreas histology, autoantibodies to glutamic acid decarboxylase (GAD65), IA‐2, and insulin by standardized radioligand‐binding assays as well as antibodies to in vitro transcribed and translated Ljungan virus antigens. Group A represented 101 trapped bank voles, which were screened for diabetes when euthanized within 24 hours of capture. Group B represented 67 bank voles, which were trapped and kept in the laboratory for 1 month before being euthanized. Group A bank voles did not have diabetes. Bank voles in group B (22/67; 33%) developed diabetes due to specific lysis of pancreatic islet beta cells. Compared to nondiabetic group B bank voles, diabetic animals had increased levels of GAD65 ( P < .0001), IA‐2 ( P < .0001), and insulin ( P = .03) autoantibodies. Affected islets stained positive for Ljungan virus, a novel picorna virus isolated from bank voles. Ljungan virus inoculation of nondiabetic wild bank voles induced beta‐cell lysis. Compared to group A bank voles, Ljungan virus antibodies were increased in both nondiabetic ( P < .0001) and diabetic ( P = .0015) group B bank voles. Levels of Ljungan virus antibodies were also increased in young age at onset of newly diagnosed type 1 diabetes in children ( P < .01). These findings support the hypothesis that the development of type 1 diabetes in captured wild bank voles is associated with Ljungan virus. It is speculated that bank voles may have a possible zoonotic role as a reservoir and vector for virus that may contribute to the incidence of type 1 diabetes in humans.
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