Katrine Eldegard

Female offspring desertion and male-only care increase with natural and experimental increase in food abundance

In species with biparental care, one parent may escape the costs of parental care by deserting and leaving the partner to care for the offspring alone. A number of theoretical papers have suggested a link between uniparental offspring desertion and ecological factors, but empirical evidence is scarce. We investigated the relationship between uniparental desertion and food abundance in a natural population of Tengmalms owl Aegolius funereus, both by means of a 5-year observational study and a 1-year experimental study. Parents and offspring were fitted with radio-transmitters in order to reveal the parental care strategy (i.e. care or desert) of individual parents, and to keep track of the broods post-fledging. We found that 70 per cent of the females from non-experimental nests deserted, while their partner continued to care for their joint offspring alone. Desertion rate was positively related to natural prey population densities and body reserves of the male partner. In response to food supplementation, a larger proportion of the females deserted, and females deserted the offspring at an earlier age. Offspring survival during the post-fledging period tended to be lower in deserted than in non-deserted broods. We argue that the most important benefit of deserting may be remating (sequential polyandry).

Experimental increase in food supply influences the outcome of within-family conflicts in Tengmalm’s owl

Within a family there are conflicts of interest between parents and offspring, and between male and female parents, over the supply of parental care. The observed pattern of parental care is the outcome of negotiations within the family, and may be influenced by environmental factors such as food abundance. We experimentally increased food supply to ten Tengmalm’s owl (Aegolius funereus) nests from hatching to fledging, mimicking natural cached prey. Ten un-supplemented nests served as controls. Parents and offspring were fitted with radio-tags. Food provisioning by parents was measured both in the (1) mid- and (2) late nestling stage and in the (3) early and (4) late post-fledging stage. In response to food supplementation, both males and females reduced food provisioning, but the effect was more pronounced in females. Females generally contributed much less to food provisioning than males, and food supplementation increased the difference between the sexes. Mass loss during the brooding stage was substantially lower for supplemented than for control females. Food supplementation did not improve offspring survival, and had no effect on body measurements of nestlings. In conclusion, parents of both sexes used the increased food supply to reduce the costs of caring for their current offspring, but females responded more strongly than males.

Sex roles during post-fledging care in birds: female Tengmalm's Owls contribute little to food provisioning

AbstractPost-fledging care constitutes a large proportion of the total costs of parental care in many bird species. Despite being recognized as of critical importance to the survival of the offspring and their recruitment into the breeding population, post-fledging care, including the relative contribution by male and female parents, is under-studied. In this study, we quantified food provisioning (prey deliveries) by male and female Tengmalm’s Owl (Aegolius funereus) parents to their offspring both in the nestling and the post-fledging stages, in years of differing natural prey abundance. Parents and at least one offspring in 26 families were fitted with radio-transmitters. Male parents exhibited higher delivery rates than did females throughout the late nestling and post-fledging stages, but the intersexual difference was smaller in broods that were not deserted by the female at any stage. The female deserted her mate and offspring at some stage in 63% of the broods. Overall, deserted males delivered more prey to their offspring than did non-deserted males. Delivery rates were generally higher post-fledging. Prey delivery rates differed among years, and were highest in low vole years (probably because of smaller prey items), intermediate in peak vole years, and lowest in years of vole increase. Prey delivery rates increased with increasing brood size for both sexes, but the response was stronger in females. We suggest that female Tengmalm’s Owls contribute less than males because they are in a position to decide on their level of provisioning effort first, and because of the potential for re-mating after deserting the first brood.ZusammenfassungGeschlechterrollen bei der Fürsorge für Flügglinge: Weibliche Raufußkäuze tragen wenig zur Futterversorgung bei Die Fürsorge für Flügglinge macht bei vielen Vogelarten einen großen Anteil der Gesamtkosten der Brutpflege aus. Obwohl bekannt ist, dass die Fürsorge für Flügglinge von entscheidender Bedeutung für das Überleben der Nachkommen und ihre Rekrutierung in die Brutpopulation ist, ist dieser Aspekt der Brutpflege, einschließlich des relativen Beitrags von Männchen und Weibchen, nicht gut untersucht. In dieser Studie haben wir in Jahren mit unterschiedlicher natürlicher Beuteabundanz quantifiziert, wie männliche und weibliche Raufußkäuze (Aegolius funereus) ihre Nachkommen mit Futter versorgten, sowohl im Nestlingsstadium als auch nach dem Ausfliegen. Die Elternvögel und mindestens ein Jungvogel aus 26 Familien wurden mit Radiosendern ausgestattet. Männchen wiesen während des späten Nestlingsstadiums und nach dem Ausfliegen höhere Fütterraten auf als Weibchen, aber der Unterschied zwischen den Geschlechtern war geringer in Bruten, die nicht zu irgendeinem Zeitpunkt vom Weibchen verlassen wurden. Das Weibchen verließ irgendwann seinen Partner und seine Nachkommen in 63% der Bruten. Insgesamt brachten verlassene Männchen ihren Nachkommen mehr Beute als nicht verlassene. Die Fütterraten waren nach dem Ausfliegen generell höher. Sie unterschieden sich zwischen den Jahren und waren am höchsten in Jahren mit geringer Wühlmausabundanz (wahrscheinlich aufgrund kleinerer Beutestücke), mittel in Jahren mit höchster Wühlmausabundanz und niedrig in Jahren mit zunehmender Wühlmausabundanz. Die Fütterraten nahmen mit ansteigender Brutgröße für beide Geschlechter zu, doch die Antwort war bei Weibchen stärker ausgeprägt. Wir schlagen vor, dass weibliche Raufußkäuze einen geringeren Beitrag leisten als Männchen, da sie in der Lage sind, über das Ausmaß ihres Fütterungsaufwands zuerst zu entscheiden, und für sie die Möglichkeit besteht, sich nach Verlassen der ersten Brut wieder zu verpaaren.

Coping in a human-dominated landscape: trade-off between foraging and keeping away from roads by moose (Alces alces)

Roads fragment moose habitat and cause increased mortality through moose–vehicle collisions. Previous studies have found that moose avoid areas near roads. In late winter, when moose face depleting food resources elsewhere, moose may be more prone to use areas near roads for foraging. However, this presumed trade-off between foraging and keeping away from roads has not previously been investigated. We sampled positions from global positioning system-collared moose in late winter from a high-density moose population in Southern Norway that is heavily influenced by human infrastructure. We combined data on moose positions with detailed field surveys of food abundance at sites that were, respectively, intensively used or sparsely used by moose. The probability that a site was intensively used increased with increasing abundance of high-quality browse and also with increasing distance to the nearest road. This indicates that moose trade-off foraging against keeping away from roads. We also found that spatio-temporal movements in relation to roads were influenced by variation in perceived human-derived risk; moose moved closer to smaller roads (low traffic volume) than to major roads (higher traffic volume) and closer to roads at night than at day. Males moved closer to roads than females. In conclusion, moose clearly exhibited behavioural adaptations to cope with roads and traffic in the study area. Because availability of high-quality forage substantially influenced habitat use, it may be an option to establish artificial feeding sites during winter to keep moose away from the roads.

The effects of habitat management on the species, phylogenetic and functional diversity of bees are modified by the environmental context.

Abstract Anthropogenic landscape elements, such as roadsides, hedgerows, field edges, and power line clearings, can be managed to provide important habitats for wild bees. However, the effects of habitat improvement schemes in power line clearings on components of diversity are poorly studied. We conducted a large‐scale experiment to test the effects of different management practices on the species, phylogenetic, and functional diversity of wild bees in power line clearings (n = 19 sites across southeastern Norway) and explored whether any treatment effects were modified by the environmental context. At each site, we conducted the following treatments: (1) Cut: all trees cut and left to decay in the clearing; (2) Cut + Remove: all trees cut and removed from the plot; and (3) Uncut: uncleared. The site‐specific environmental context (i.e., elevation and floral diversity) influenced the species, phylogenetic, and functional diversity within bee species assemblages. The largest number of species was found in the Cut + Remove treatment in plots with a high forb species richness, indicating that the outcome of management practices depends on the environmental context. Clearing of treatment plots with many forb species also appeared to alter the phylogenetic composition of bee species assemblages, that is, more closely related species were found in the Cut and the Cut + Remove plots than in the Uncut plots. Synthesis and applications: Our experimental simulation of management practices in power line clearings influenced the species, phylogenetic, and functional diversity of bee species assemblages. Frequent clearing and removal of the woody debris at low elevations with a high forb species richness can increase the value of power line clearings for solitary bees. It is therefore important for managers to consider the environmental context when designing habitat improvement schemes for solitary bees.

Spatio-temporal variation in species assemblages in field edges: seasonally distinct responses of solitary bees to local habitat characteristics and landscape conditions

Abstract The bees (Hymenoptera: Apiformes) are important pollinators in many ecosystems, but their diversity has declined in Europe during the past century, mainly due to habitat loss. However, some of the habitat requirements of wild bees are met in anthropogenic landscape elements, such as road sides, power-line strips and field edges. Moreover, as the bee species assemblages change throughout the season the habitat requirements of the bee fauna may change accordingly. Understanding such seasonally distinct responses of solitary bees with different phenologies may be of high value for local conservation planning. The purpose of this study was to examine if the habitat quality of field edges for solitary bees change throughout the season, and how this temporal variation relates to local habitat and landscape conditions. By sampling solitary bees in 18 field edges in southeast Norway throughout the season we found that the species richness and abundance of bees was highest in sun exposed field edges, independently of the season. However, we found phenologically distinct responses to the landscape context. Moreover, field edges situated in landscapes with a high proportion of forests and semi-natural landscape elements hosted the most phenologically diverse bee species assemblages. We conclude that in order to fulfil the habitat requirements of bee species assemblages throughout the season, one should conserve and direct habitat restoration schemes towards increasing sun exposure at field edges with a diverse flora and a high proportion of semi-natural areas in the vicinity.

Modelling bird richness and bird species presence in a boreal forest reserve using airborne laser-scanning and aerial images

Capsule Variables obtained from airborne laser-scanning (ALS) enabled slight or fair predictions of bird presence, and including multispectral data further improved predictions slightly. Aims To assess the usefulness of ALS as a tool for predicting species richness and single-species presence, and to investigate if including information from multispectral aerial images further improved predictability of bird presence. Methods Bird presence data were sampled in a Norwegian boreal forest reserve. Prediction models were developed for species richness and presence of the eight most abundant species by the use of two different modelling approaches: generalized linear models and the machine learning method random forest. Predictor variables were descriptors of three-dimensional forest structure obtained by ALS, and descriptors of tree species composition obtained from multispectral aerial images. Results Cross-validation of the prediction models indicated overall slight or fair predictive capability. Best predictions were obtained for Goldcrest, Wren, and Willow Warbler. Inclusion of spectral variables derived from the aerial imagery slightly improved the predictive performance of several models, most notably for Willow Warbler. Conclusion We suggest that predictability of species richness and presence of single bird species can be improved by better matching of the scale of recording for birds and the predictor variables obtained by remote sensing.

Inter-assemblage facilitation: the functional diversity of cavity-producing beetles drives the size diversity of cavity-nesting bees

Abstract Inter‐specific interactions are important drivers and maintainers of biodiversity. Compared to trophic and competitive interactions, the role of non‐trophic facilitation among species has received less attention. Cavity‐nesting bees nest in old beetle borings in dead wood, with restricted diameters corresponding to the body size of the bee species. The aim of this study was to test the hypothesis that the functional diversity of cavity‐producing wood boring beetles ‐ in terms of cavity diameters ‐ drives the size diversity of cavity‐nesting bees. The invertebrate communities were sampled in 30 sites, located in forested landscapes along an elevational gradient. We regressed the species richness and abundance of cavity nesting bees against the species richness and abundance of wood boring beetles, non‐wood boring beetles and elevation. The proportion of cavity nesting bees in bee species assemblage was regressed against the species richness and abundance of wood boring beetles. We also tested the relationships between the size diversity of cavity nesting bees and wood boring beetles. The species richness and abundance of cavity nesting bees increased with the species richness and abundance of wood boring beetles. No such relationship was found for non‐wood boring beetles. The abundance of wood boring beetles was also related to an increased proportion of cavity nesting bee individuals. Moreover, the size diversity of cavity‐nesting bees increased with the functional diversity of wood boring beetles. Specifically, the mean and dispersion of bee body sizes increased with the functional dispersion of large wood boring beetles. The positive relationships between cavity producing bees and cavity nesting bees suggest that non‐trophic facilitative interactions between species assemblages play important roles in organizing bee species assemblages. Considering a community‐wide approach may therefore be required if we are to successfully understand and conserve wild bee species assemblages in forested landscapes.

Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion

Abstract Vast areas of the African savanna landscapes are characterized by tree‐covered Macrotermes termite mounds embedded within a relatively open savanna matrix. In concert with termites, large herbivores are important determinants of savanna woody vegetation cover. The relative cover of woody species has considerable effects on savanna function. Despite the potentially important ecological relationships between termite mounds, woody plants, large herbivores, and birds, these associations have previously received surprisingly little attention. We experimentally studied the effects of termites and large herbivores on the avian community in Lake Mburo National Park, Uganda, where woody vegetation is essentially limited to termite mounds. Our experiment comprised of four treatments in nine replicates; unfenced termite mounds, fenced mounds (excluding large mammals), unfenced adjacent savanna, and fenced savanna. We recorded species identity, abundance, and behavior of all birds observed on these plots over a two‐month period, from late dry until wet season. Birds used termite mounds almost exclusively, with only 3.5% of observations occurring in the treeless intermound savanna matrix. Mean abundance and species richness of birds doubled on fenced (large herbivores excluded) compared to unfenced mounds. Feeding behavior increased when large mammals were excluded from mounds, both in absolute number of observed individuals, and relative to other behaviors. This study documents the fundamental positive impact of Macrotermes termites on bird abundance and diversity in an African savanna. Birds play crucial functional roles in savanna ecosystems, for example, by dispersing fruits or regulating herbivorous insect populations. Thus, the role of birds in savanna dynamics depends on the distribution and abundance of termite mounds.

Intersexual difference in early natal dispersal: abrupt departure by females and gradual emigration by males in Tengmalm’s Owl Aegolius funereus

AbstractThe decision to emigrate from the natal area can influence future fitness prospects, yet detailed data on sex-specific juvenile dispersal behaviour is still lacking for most bird species. We tracked 13 radio-tagged Tengmalm’s Owl Aegolius funereus juveniles from 13 different nests from fledging to independence and onwards. Six out of the seven female juveniles departed abruptly and disappeared from the natal area. In contrast, only one male juvenile departed abruptly, whereas the other five males and one female remained in the study area until tracking was terminated. We propose two alternative interpretations: (1) females initiated natal dispersal earlier than males, or (2) the manner of dispersal differed between the sexes, with females departing abruptly, and males moving gradually out of the natal area. We found no statistically significant influence of body condition or date of independence on dispersal behaviour. We suggest that early onset of dispersal and fast movements out of the natal area may increase a juvenile female’s chances of successful breeding in the following spring. In contrast to females, male Tengmalm’s Owls rarely breed as 1-year-olds, and the benefits of early/abrupt dispersal may be lower for juvenile males. We suggest that female-biased natal dispersal in Tengmalm’s Owl may come about through relatively higher lifetime reproductive success of early dispersing in females than in males.ZusammenfassungGeschlechtsspezifische Unterschiede in der frühen Jugendstreuung: Abruptes Verlassen bei Weibchen und graduelles Abwandern bei Männchen beim RaufußkauzAegolius funereus Die Entscheidung zur Abwanderung vom Geburtsort kann die zukünftige Fitness beeinflussen. Dennoch fehlen detaillierte Daten zum geschlechtsspezifischen Abwanderungsverhalten der Jungvögel bei den meisten Vogelarten. Wir haben 13 junge Raufußkäuze Aegolius funereus aus 13 verschiedenen Nestern vom Ausfliegen bis zum Selbständigwerden und darüber hinaus telemetriert. Sechs der sieben jungen Weibchen verließen den Geburtsplatz abrupt. Dagegen verschwand nur ein Männchen abrupt, wogegen die anderen fünf Männchen und das eine Weibchen bis zum Ende der Untersuchung im Gebiet verblieben. Wir schlagen zwei alternative Hypothesen vor: (1) Weibchen beginnen mit der Jugendstreuung früher als Männchen, oder (2) die Geschlechter unterscheiden sich in der Art und Weise der Abwanderung, wobei die Weibchen abrupt abwandern, die Männchen dagegen graduell. Wir fanden keine signifikanten Einflüsse der Körperkondition oder des Zeitpunktes des Selbständigwerdens auf das Abwanderungsverhalten. Wir vermuten, dass das frühe und rasche Abwandern der Weibchen ihre Aussichten auf erfolgreiches Brüten im kommenden Frühjahr erhöht. Männliche Raufußkäuze brüten dagegen nur selten schon als Einjährige, weshalb bei ihnen die Vorteile eines frühen und abrupten Abwanderns geringer sind. Wir vermuten weiterhin, dass das frühere Abwandern der jungen Weibchen des Raufußkauzes einhergeht mit einem im Vergleich zu den Männchen höheren Lebenszeitbruterfolg.