Eivin Røskaft

Sex biases in avian dispersal : a reappraisal

We reviewed the avian literature for quantitative studies of sex biases in dispersal and found continued and strengthened support for the general pattern of female biased dispersal established by Greenwood in 1980. We report sex differences in dispersal patterns in natal and breeding dispersal as measured by 1) proportion leaving and 2) distance moved. Greenwoods review found evidence for male biased dispersal only within four species of the Anatidae. We find there is now evidence for male biased dispersal in twenty-two species representing twelve families.

Life History Variation, Population Processes and Priorities in Species Conservation: Towards a Reunion of Research Paradigms

We argue that a relationship between life history variation and population processes may form the foundation for developing a theory for variation in population growth rate. An examination of the distribution of 104 European bird species in relation to their clutch size and adult survival rate showed three different clusters. First, there is a large group of species which lay a large number of eggs and have low adult survival rate. The second cluster consists of species with very high survival rates and a clutch size of only one egg. The third group is characterized by species with high survival rates but still a relatively large clutch size. From these clusters of life history characteristics we argue that the species can be classified according to the quality of their survival and breeding habitats, respectively. The high-reproductive species live in favourable breeding habitats, but poor survival habitat. In contrast, the survival habitat of the survivorship species are very good, but the breeding habitats are poor. The bet-hedging species live in favourable breeding and survival habitats, but the annual variation in the quality of the breeding habitats is very large, favouring the evolution of a larger clutch size than in the survivorship species. In order to examine the effects of these patterns of covariation between life history traits on population dynamics we calculated the sensitivity and elasticity of population growth rate to a change in age-specific fecundity or mortality rates for one species from each of the three life history types. These analyses showed that population growth rates of high-reproductive species were more sensitive and elastic to changes in the fecundity among the younger age-classes, compared to the species from the two other groups. Furthermore, elasticity to variation in mortality rates was higher than to variation in fecundity rates in all three species. To provide a further link between life history variation and population dynamics the results from key-factor analyses of population fluctuations in birds and mammals were reviewed. In most altricial birds, the key-factor appears during the non-breeding season. In contrast, in precocial birds key-factors from the breeding season explained a higher proportion of the variance in the total losses than the losses during the non-breeding season. In the majority of the cases density-dependence was found in the losses during the non-breeding season. According to the Allee-effect, we would expect that the population growth rate should decrease with density at low population sizes. No evidence was found for the presence of an Allee-effect in the studies of 11 bird species which were reduced to very low population levels during the study period. We suggest however that such an Allee-effect still may be important due to a reduction in the defence efficiency among predators or parasites, reduction in mating efficiency, or reduction in the foraging efficiency at low population densities. These results may have some important implications for overall priorities in the development of strategies for conserving species diversity. In particular, we focus on the securing of survival habitats for especially longlived species outside the breeding season.

Factors influencing conservation attitudes of local people in western Serengeti Tanzania

Attitudinal studies are increasingly being adopted as tools for evaluating public understanding, acceptance and the impact of conservation interventions. The findings of these studies have been useful in guiding the policy interventions. Many factors affect conservation attitudes positively or negatively. The factors inspiring positive attitudes are likely to enhance the conservation objectives while those inducing negative attitudes may detrimentally undermine these objectives. The magnitude of the resultant effects of each particular factor is determined by the historical, political, ecological, socio-cultural and economic conditions and this may call for different management interventions. In this study we examined how conservation attitudes in western Serengeti are shaped by the following factors: level of conflicts with protected areas; wildlife imposed constraints (inadequate pasture, water, diseases, loss of livestock during migration, theft and depredation); participation in the community based project; and socio-demographic factors (age, education level, wealth, immigration, gender and household size). The results indicated that the level of conflicts, participation in the community based project, inadequate pasture, lack of water, diseases, wealth and education were important in shaping peoples’ attitudes. However, in a stepwise linear regression analysis, 59% of the variation in peoples’ attitudes was explained by three variables i.e., conflict level with protected areas, lack of water and participation in the community based project. In addition to these variables, level of education also contributed in explaining 51% of the variation in people’s attitude regarding the status of the game reserves. Five variables (lack of water, level of education, inadequate pasture, participation in the community based project and diseases) explained 12% of the variation in people’s attitude towards Serengeti National Park. The paper discusses the implications for conservation of these results and recommends some measures to realise effective conservation of wildlife resources.

Adaptations of meadow pipits to parasitism by the common cuckoo

SummaryThe meadow pipit Anthus pratensis is one of the most frequent hosts in Europe parasitized by the common cuckoo Cuculus canorus. The cuckoo normally removes one or more of the host eggs and replaces them with one of its own. The aim of the present study, which was conducted in an upland area of Central Norway, was to test the following question: assuming the cuckoo has laid a mimetic egg (which is slightly larger than and slightly different in color from that of a meadow pipit egg), under what circumstances are the parent meadow pipits able to detect such parasitism? The reaction of the meadow pipits to artificial parasitism was tested. Plastic model cuckoo eggs were used that bore a striking resemblance to real cuckoo eggs found in other meadow pipit nests in the same area. In addition, in some experiments a stuffed cuckoo dummy was used. The meadow pipits tolerated the experimental procedures and remained in their nests when given an artificial cuckoo egg, with or without removal of one of the hosts eggs. However, when a host egg was removed and replaced with an artificial cuckoo egg, and at the same time a stuffed cuckoo dummy was presente, 50% of the birds deserted their nests. The difference between this result and the results of the other experiments was statistically significant. When only the stuffed cuckoo was presented, without any egg manipulations, the meadow pipits reacted in the same way as in the egg experiments. We conclude that the meadow pipit is capable of detecting whether or not its nest has been parasitized, provided it has observed the cuckoo near the nest site. Furthermore, because of the results of our experiments, we reject the hypothesis that the cuckoo has evolved egg removal behavior in order to prevent the host from assessing an increase in egg numbers.

Patterns of self-reported fear towards large carnivores among the Norwegian public

Abstract In this paper, we analyse self-reported fear of four large carnivore species in a representative sample of the Norwegian population. People reported the most fear of the two largest and most dangerous carnivores, brown bears and wolves, and less fear of lynx and wolverines. Women expressed significantly more fear of these species than did men, and expressed fear increased with age in both sexes. Human population density had very little effect on the degree of self-reported fear of large carnivores, but people living in rural areas with one carnivore species in their vicinity expressed less fear of this species than people from rural areas where this carnivore species was absent. Activities related to experience with, or knowledge of, the large carnivores also effected fear patterns. People with higher education and those who expressed interest in outdoor activities like small game hunting and mountain hiking generally reported less fear than did respondents with lower education and no interest in outdoor activities, respectively. We argue that a good management strategy is to develop educational programs where people learn about the biology and habits of the large carnivores and are encouraged to gain first-hand outdoor experience in areas with large carnivores

Human attitudes towards large carnivores in Norway

Abstract Many factors influence human attitudes towards large carnivores. In our study we explore different factors that affect attitudes towards four such species, i.e. wolverines Gulo gulo, lynx Lynx lynx, brown bears Ursus arctos and wolves Canis lupus. We examined attitudes through a representative sample of the Norwegian population. By using 12 independent variables chosen for this study, we were able to explain around 15-45% of the variance in attitudes towards the four species. In general, people displayed more negative attitudes towards wolves and bears than towards lynx and wolverines. However, they were more positive towards increasing the small populations of the first two species than the relatively large populations of the last two. The results showed that 34-44% of the respondents reacted negatively to the question ‘What do you think should be done about the size of the carnivore population?’. On the other hand, 73-87% reacted positively to the question ‘Do these species have a right to exist in Norway?’. To the question ‘How far do you want the carnivore species from your home?’, 41-66% answered > 10 km. The most important variables explaining negative attitudes towards all the large carnivore species regarded the concern of the respondents for their own and their familys safety. People became more negative with age; those who were afraid of the carnivores were in general more negative towards them, and those who experienced financial loss (i.e. farmers) by having large carnivores in their vicinity expressed negative attitudes. On the other hand, the excitement of seeing large carnivores in their natural environment had a positive influence on attitude. People from larger communities were in general more positive, whereas those who thought they had the species in their vicinity were more negative. Big-game hunters frequently showed negative attitudes, whereas those with higher levels of education tended to be more positive. Our results indicate that attitudes towards large carnivores are complex. However, people are in general more negative towards wolves and bears, which must be taken into account in conservation programmes.

Rejection of artificial cuckoo (Cuculus canorus) eggs in relation to variation in egg appearance among reed warblers (Acrocephalus scirpaceus)

Passerines that are exposed to brood parasitism can evolve reduced intraclutch variation in egg appearance to facilitate recognition and rejection of the parasitic egg. This has been shown to be true for European passerine species that are assumed to have participated in an evolutionary arms race with the cuckoo (Cuculus canorus). However, few investigations have been carried out with the aim of finding out whether there is a relationship between these two traits within a species. In this study, we compare the level of intraclutch variation in egg appearance and the rejection of an unlike parasitic egg within a population of reed warblers (Acrocephalus scirpaceus) in the south-eastern part of the Czech Republic. We parasitized reed warbler nests with an artificial non–mimetic cuckoo egg, and then monitored the reaction of the hosts. In 27 out of 48 nests (56.3%) the parasitic egg was rejected. The rejecter pairs had a statistically significantly lower intraclutch variation in egg appearance than the acceptor pairs. We discuss possible explanations for the observed relationship between rejection of unlike eggs and intraclutch variation in egg appearance within this population of reed warblers. The results are consistent with the evolutionary arms race hypothesis, but the intermediate rejection rate found in this population could also be maintained by an equilibrium between acceptors and rejecters due to rejection costs.

The relationship between social status and resting metabolic rate in great tits (Parus major) and pied flycatchers (Ficedula hypoleuca)

The oxygen consumption of great tits (Parus major) in winter flocks and of male pied flycatchers (Ficedula hypoleuca) in breeding condition, was measured. Resting metabolic rate was significantly correlated with dominance rank, as expressed by the width of the breast-stripe in the great tits and the darkness of the plumage on the head and back, or date of pair-formation, in males of the pied flycatcher. Individuals with the highest metabolic rates were the most dominant ones. Similarly, heart weight, relative to body weight, in dominant great tits was greater than that in lower-ranking birds.

Constraints on host choice: why do parasitic birds rarely exploit some common potential hosts?

1. Why are some common and apparently suitable resources avoided by potential users? This interesting ecological and evolutionary conundrum is vividly illustrated by obligate brood parasites. Parasitic birds lay their eggs into nests of a wide range of host species, including many rare ones, but do not parasitize some commonly co-occurring potential hosts. 2. Attempts to explain the absence of parasitism in common potential hosts are limited and typically focused on single-factor explanations while ignoring other potential factors. We tested why thrushes Turdus spp. are extremely rarely parasitized by common cuckoos Cuculus canorus despite breeding commonly in sympatry and building the most conspicuous nests among forest-breeding passerines. 3. No single examined factor explained cuckoo avoidance of thrushes. Life-history traits of all six European thrush species and the 10 most frequently used cuckoo hosts in Europe were similar except body/egg size, nest design and nestling diet. 4. Experiments (n = 1211) in several populations across Europe showed that host defences at egg-laying and incubation stages did not account for the lack of cuckoo parasitism in thrushes. However, cross-fostering experiments disclosed that various factors during the nestling period prevent cuckoos from successfully parasitizing thrushes. Specifically, in some thrush species, the nest cup design forced cuckoo chicks to compete with host chicks with fatal consequences for the parasite. Other species were reluctant to care even for lone cuckoo chicks. 5. Importantly, in an apparently phylogenetically homogenous group of hosts, there were interspecific differences in factors responsible for the absence of cuckoo parasitism. 6. This study highlights the importance of considering multiple potential factors and their interactions for understanding absence of parasitism in potential hosts of parasitic birds. In the present study, comparative and experimental procedures are integrated, which represent a novel approach that should prove useful for the understanding of interspecific ecological relationships in general.

OBLIGATE BROOD PARASITES AS SELECTIVE AGENTS FOR EVOLUTION OF EGG APPEARANCE IN PASSERINE BIRDS

Abstract Many passerine host species have counteracted the parasite egg mimicry in their coevolutionary arms race with the common cuckoo (Cuculus canorus) by evolving increased interclutch and reduced intraclutch variation in egg appearance. Such variations make it easier for hosts to recognize a foreign egg, reduce the possibility of making recognition errors, and reduce the ability of the cuckoo to mimic the eggs of a particular host. Here, we investigate if such clutch characteristics have evolved among North American passerines. We predict that due to the absence of brood parasites with egg mimicry on this continent, these passerines should (1) not show any relationship between rejection rates and intra‐ or interclutch variation, and (2) intraclutch variation should be lower and interclutch variation higher in European hosts exposed to cuckoo parasitism as compared to North American hosts parasitized by cowbirds. Here we present data that show support for most of these and other predictions, as well as when controlling statistically for effects of common descent. However, the effect of continent on intraclutch variation was less than predicted and we discuss a possible reason for this. All things considered, the results demonstrate that parasitism by a specialist brood parasite with egg mimicry is a powerful selective force regarding the evolution of egg characteristics in passerine birds.