The importance of visual cues for nocturnal species: eagle owls signal by badge brightness

Nocturnal species may communicate by visual signals more frequentlythan previously thought. In fact, such species are habituallyactive around sunset and sunrise, when light conditions arestill suitable for visual communication. We investigated thecommunication function of a visual cue in the eagle owl Bubobubo, a nocturnal predator. In this species, territorial andcourtship displays peak during the sunset and sunrise periodsand involve the display of a white badge located on the throatwhose reflectance properties are sex and period dependent. Experimentalintrusions were conducted at 30 eagle owl territories in orderto understand the function of the white badge during contests.We analyzed the reactions of both male and female owners towarda taxidermic mount with a normal brightness and a brightness-reducedwhite badge, with both male and female territorial calls. Ourresults indicate that the white badge of eagle owls plays animportant role in visual communication during contests. Malesdisplayed more frequently toward male low-brightness mounts,which were also approached more closely or attacked. Femalebehavior did not differ between experimental groups. Furthermore,a positive relationship between male badge brightness and breedingoutput suggested a potential role of the white badge as an honestsignal of male quality. The need to convey information by visualcommunication in a nocturnal species may have promoted the evolutionof visual signals employed at crepuscule.     

Simultaneous effects of age and territory quality on fecundity in Bonelli's Eagle Hieraaetus fasciatus

Several factors that interact with a bird's age are likely to affect breeding performance. Because of habitat heterogeneity, individuals of different subpopulations may experience different probabilities of breeding, depending on the habitat that they occupy. The aim of this work is to test the hypothesis that age and territory quality independently affect breeding performance. We analysed data on breeding biology and fecundity at 298 breeding sites of Bonelli's Eagle Hieraaetus fasciatus in Andalusia from 1980 to 2000. Our data confirmed that age and territory quality simultaneously affect reproductive output. After controlling for the effect of year and age, breeding performance varied among territories. Independently of territory quality, the age of breeding birds affected the number of fledged young and variance in productivity.     

Denning in brown bears

1. Hibernation represents an adaptation for coping with unfavorable environmental conditions. For brown bears Ursus arctos, hibernation is a critical period as pronounced temporal reductions in several physiological functions occur.
2. Here, we review the three main aspects of brown bear denning: (1) den chronology, (2) den characteristics, and (3) hibernation physiology in order to identify (a) proximate and ultimate factors of hibernation as well as (b) research gaps and conservation priorities.
3. Den chronology, which varies by sex and reproductive status, depends on environmental factors, such as snow, temperature, food availability, and den altitude. Significant variation in hibernation across latitudes occurs for both den entry and exit.
4. The choice of a den and its surroundings may affect individual fitness, for example, loss of offspring and excessive energy consumption. Den selection is the result of broad‐ and fine‐scale habitat selection, mainly linked to den insulation, remoteness, and availability of food in the surroundings of the den location.
5. Hibernation is a metabolic challenge for the brown bears, in which a series of physiological adaptations in tissues and organs enable survival under nutritional deprivation, maintain high levels of lipids, preserve muscle, and bone and prevent cardiovascular pathologies such as atherosclerosis.

It is important to understand: (a) proximate and ultimate factors in denning behavior and the difference between actual drivers of hibernation (i.e., factors to which bears directly respond) and their correlates; (b) how changes in climatic factors might affect the ability of bears to face global climate change and the human‐mediated changes in food availability; (c) hyperphagia (period in which brown bears accumulate fat reserves), predenning and denning periods, including for those populations in which bears do not hibernate every year; and (d) how to approach the study of bear denning merging insights from different perspectives, that is, physiology, ecology, and behavior.     

When individuals senesce: the 'Florida effect' on stable populations of territorial, long-lived birds

Senescence can be defined as the entire set of age-related changes that affect both vitality and function, one of which is within-individual age-related decline in reproduction. This factor is crucial for population persistence, because the senescence of individuals of a population can increase the likelihood of local extinction. Using simulations based on long-term information on a small metapopulation of a long-lived bird species, we highlight two mechanisms able to engender senescence in both breeders and floaters (i.e. non-breeding individuals) of the same population. We define 'floater shortage senescence' as breeder senescence due to low juvenile replacement rates because of high floater mortality during dispersal. Less obviously, senescence can also occur with very low floater mortality rates, and when breeding populations are remarkably free from factors that could cause catastrophic population decimation. In this scenario, low mortality in reproductive areas results in territory owners in breeding populations being characterised by progressively older breeding individuals, and old individuals waiting for a breeding opportunity: a phenomenon we refer to as the 'Florida effect'. Consistent with current views that adaptive death plays a crucial role in population dynamics, it seems reasonable to suppose that, under stable environmental conditions, the evolution of some mating mechanisms could limit the senescence of breeding individuals in a population, allowing the pool of breeding individuals to be refreshed by selection of younger breeders.     

Population Characteristics May Reduce the Levels of Individual Call Identity

Individual variability influences the demographic and evolutionary dynamics of spatially structured populations, and conversely ecological and evolutionary dynamics provide the context under which variations at the individual level occur. Therefore, it is essential to identify and characterize the importance of the different factors that may promote or hinder individual variability. Animal signaling is a prime example of a type of behavior that is largely dependent on both the features of individuals and the characteristics of the population to which they belong. After 10 years studying the dynamics of a population of a long-lived species, the eagle owl (Bubo bubo), we investigated the emergence and maintenance of traits that reveal individual identity by focusing on vocal features. We found that individuals inhabiting a high density population characterized by a relative lack of heterogeneity (in terms of prey availability and breeding success) among breeding sites might be selected for reducing the levels of identity. Two non-mutually exclusive hypotheses may explain the structural call patterns we detected: (1) similarity in calls may be principally a consequence of the particular characteristics of the population; and (2) high density may encourage individuals to mimic each other’s vocalizations in a cascade effect, leading to a widespread and unique communication network.     

Evaluating the influence of diet-related variables on breeding performance and home range behaviour of a top predator

Diet composition is linked to reproductive performance directly or indirectly by other life-history traits, including home range behaviour. The relationships between prey abundance, diet and individual fitness have often been explored. However, these relationships are complex and difficult to disentangle, especially in vertebrate top predators. Here, we present the results of a long-term study using multi-model inference procedures to elucidate the influence of diet-related variables on breeding parameters and home range behaviour of a top predator, the eagle owl Bubo bubo. Superpredation, diet diversity, rat biomass and rabbit mean weight were the most important variables when analysing reproductive parameters, suggesting that less diverse diets with greater rabbit biomass percentage may benefit reproductive performance, whereas rat biomass percentage is apparently associated with greater variation of breeding success. Earlier laying dates seem to be associated with the consumption, on average, of smaller rabbits. On the other hand, edge density was the most relevant factor determining the variation in home range behaviour, with individual characteristics, such as age and sex, also being important. Although the relative importance of the diet-related variables was generally low, mean weight of alternative prey, diet diversity and rabbit biomass also helped to explain home range parameters. In an optimal foraging context, centred on the abundance of the main prey species, our results suggest that when rabbits are less available eagle owls may increase home range size in order to obtain alternative prey, increasing at the same time their dietary diversity, which may also require higher movement speed.     

Individual attributes and party affect large carnivore attacks on humans

Wildlife managers, researchers and the general public have traditionally been demanding information on factors concerning the probability of risky encounters between predators and people, as well as how to react in those situations. This information is crucial to reduce the number of predator attacks, which in absolute terms have increased in the last decades. Here, we focus on the role of carnivore species and sex, as well as victim-related factors (i.e. gender, activities, party composition), as determinants of carnivore attacks on humans. Using a dataset on attacks by grizzlies (Ursus arctos horribilis), black bears (Ursus americanus), cougars (Puma concolor), wolves (Canis lupus) and coyotes (Canis latrans) in North America during the last five decades, we found that (1) male black bears were involved in attacks more frequently than females; (2) attacks by coyotes, cougars and wolves prevalently caused injuries, whereas cases of death were more frequent during grizzly and black bear attacks; and (3) people in a party were less vulnerable to an attack than a person alone. We identified risky situations and behaviours that should be avoided in areas where people and large carnivore share the landscape.     

The seasonal sensitivity of brown bear denning phenology in response to climatic variability

Background

For brown bears (Ursus arctos), hibernation is a critical part of the annual life cycle because energy savings during hibernation can be crucial for overwintering, and females give birth to cubs at that time. For hibernation to be a useful strategy, timing is critical. However, environmental conditions vary greatly, which might have a negative effect on the functionality of the evolved biological time-keeping. Here, we used a long-term dataset (69 years) on brown bear denning phenology recorded in 12 Russian protected areas and quantified the phenological responses to variation in temperature and snow depth. Previous studies analyzing the relationship between climate and denning behavior did not consider that the brown bear response to variation in climatic factors might vary through a period preceding den entry and exit. We hypothesized that there is a seasonal sensitivity pattern of bear denning phenology in response to variation in climatic conditions, such that the effect of climatic variability will be pronounced only when it occurs close to den exit and entry dates.

Results

We found that brown bears are most sensitive to climatic variations around the observed first den exit and last entry dates, such that an increase/decrease in temperature in the periods closer to the first den exit and last entry dates have a greater influence on the denning dates than in other periods.

Conclusions

Our study shows that climatic factors are modulating brown bear hibernation phenology and provide a further structuring of this modulation. The sensitivity of brown bears to changes in climatic factors during hibernation might affect their ability to cope with global climate change. Therefore, understanding these processes will be essential for informed management of biodiversity in a changing world.