The use of supplementary foods by Australian magpies Gymnorhina tibicen: Implications for wildlife feeding in suburban environments

Abstract The provision of foods to wild birds is an extremely common practice among householders throughout the Western world. Nonetheless, concerns over potential impacts of the practice are currently being raised, including the possibility that some species may become reliant on human‐provided food. We compared the foraging and breeding ecology of pairs of fed and unfed Australian magpies Gymnorhina tibicen living in suburban environments in Brisbane, Queensland, Australia. Detailed behavioural observations of both foraging and chick provisioning were made for males and females of both groups throughout the breeding season. Natural foods dominated the diets of both fed and unfed magpies, making up 76% and 92% of all items consumed respectively. During the morning, fed magpies obtained fewer food items during ground foraging than did unfed birds, apparently because they visited suburban feeding stations more often during the early part of the day. At other times, the amount of food items obtained during foraging was similar for both fed and unfed birds. Magpies utilizing suburban feeding stations started all breeding activities significantly earlier than unfed magpies, except during the fledgling phase. Both fed and unfed magpie parents provisioned their chicks predominantly with natural food. Magpies were not reliant or dependent on supplementary food provided by wildlife feeders at any time during the breeding season. Although many magpies did utilize suburban feeding stations extensively, they continued to forage for and provision their chicks with natural food.     

小型啮齿动物种群系统调节复合因子理论的野外实验研究：食物可利用性和捕食对根田鼠种群动态作用的分析

本研究在野外围栏条件下采用析因实验设计,测定营养、捕食及空间行为对根田鼠（Ｍｉ－ｃｒｏｔｕｓｏｅｃｏｎｏｍｕｓ）种群统计特征的影响。本文旨在检验下述特定假设：高质量食物可利用性和捕食对限制小型啮齿动物种群密度具有独立的和累加的效应。３年期间,４种野外实验处理６个重复的研究结果表明,附加食物并预防捕食者处理的种群具有最高密度;未附加食物及不预防捕食者处理（对照）的种群密度最低;而单一处理的种群,其密度居中。不同处理条件下,新生个体在种群的补充模式以及种群瞬时增长率的变化均与种群密度的变动相应一致。双因素ＡＮＯＶＡ的结果证明,附加高质量食物能明显地提高根田鼠的种群密度,而对种群补充量的作用则较弱,仅接近显著水平;预防捕食者不仅能显著地作用于种群密度,更能强烈地影响种群补充量。高质量食物和捕食者的作用具有累加的性质,两者的交互作用对种群密度和补充量均无显著影响。     

From process to pattern: how fluctuating predation risk impacts the stress axis of snowshoe hares during the 10-year cycle

Predation is a central organizing process affecting populations and communities. Traditionally, ecologists have focused on the direct effects of predation—the killing of prey. However, predators also have significant sublethal effects on prey populations. We investigated how fluctuating predation risk affected the stress physiology of a cyclic population of snowshoe hares (Lepus americanus) in the Yukon, finding that they are extremely sensitive to the fluctuating risk of predation. In years of high predator numbers, hares had greater plasma cortisol levels at capture, greater fecal cortisol metabolite levels, a greater plasma cortisol response to a hormone challenge, a greater ability to mobilize energy and poorer body condition. These indices of stress had the same pattern within years, during the winter and over the breeding season when the hare:lynx ratio was lowest and the food availability the worst. Previously we have shown that predator-induced maternal stress lowers reproduction and compromises offspring’s stress axis. We propose that predator-induced changes in hare stress physiology affect their demography through negative impacts on reproduction and that the low phase of cyclic populations may be the result of predator-induced maternal stress reducing the fitness of progeny. The hare population cycle has far reaching ramifications on predators, alternate prey, and vegetation. Thus, predation is the predominant organizing process for much of the North American boreal forest community, with its indirect signature—stress in hares—producing a pattern of hormonal changes that provides a sensitive reflection of fluctuating predator pressure that may have long-term demographic consequences.     

Body mass constraints on feeding rates determine the consequences of predator loss

Understanding effects of species loss in complex food webs with multiple trophic levels is complicated by the idiosyncrasy of the predator effects on lower trophic levels: direct and indirect effects intermingle and may increase, decrease or not affect ecosystem functioning. We introduce a reductionist approach explaining a predator's trophic effect only by empirically well-founded body-mass constraints on abundance, diet breadth and feeding strength. We demonstrate that this mechanistic concept successfully explains the positive, negative and neutral net effects of predators on decomposers in a litter microcosm experiment. This approach offers a new perspective on the interplay of complex interactions within food webs and is easily extendable to include phylogenetic and other body-mass independent traits. We anticipate that allometry will substantially improve our understanding of idiosyncratic predator effects in experiments and the consequences of predator loss in natural ecosystems.     

Protective nesting association between the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio: an experiment using artificial and natural nests

The pressure of predators may significantly affects the distribution pattern of nesting birds. Some individuals may reduce the risk of predation by nesting near other species with an aggressive nest defence. In the present study I tested the predator protection hypothesis using experimental (artificial nests) and observational (real nests) approaches on two ecologically similar passerine birds–the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio. Studies have been conducted in eastern Poland in two types of habitat: river valley and farmland. The main predators of natural and artificial nests were birds, and to a lesser extent, also mammals. I found wide variation level of predation of both types of nests in different years. Nest survival rate of artificial nests was significantly lower in the farmland than in the river valley and in natural nests I observed reverse pattern. According to the predictions of the predator protection hypothesis the survival rates of the natural and artificial nests were significantly higher in territories of individuals breeding in the protective nesting association. This type of interspecific positive interaction between two associate species can be classified as facultative mutualism.     

Conserved features of chronic stress across phyla: the effects of long-term stress on behavior and the concentration of the neurohormone octopamine in the cricket, Gryllus texensis

Many of the deleterious effects of chronic stress in vertebrates are caused by the long-term elevation of stress hormones. These negative effects are thought to be unavoidable by-products of sustained activation of the stress response, but the details remain unclear. A comparative perspective may help in understanding chronic stress. We exposed crickets (Gryllus texensis) to a mock predator. A single exposure to a mock predator induced a transient increase in the hemolymph (blood) concentration of the insect stress neurohormone, octopamine. Repeated exposure to the mock predator increased basal levels of octopamine, similar to the effects of chronic stress on the basal levels of vertebrate stress hormones. This study is the first to report an increase in the basal levels of an invertebrate stress hormone in response to repeated flight-or-fight stress. Chronic stress reduced weight gain, and decreased feeding and enhanced weight loss after food deprivation in adult female crickets. However, chronic stress also increased the tendency of crickets to produce sustained flight. Therefore, this study supports the hypothesis that increasing basal levels of stress hormones may be a phylogenetically common response to chronically stressful conditions. It also demonstrates that chronic stress has both positive and negative effects in insects.     

Conserved features of chronic stress across phyla: The effects of long-term stress on behavior and the concentration of the neurohormone octopamine in the cricket,Gryllus texensis

Many of the deleterious effects of chronic stress in vertebrates are caused by the long-term elevation of stress hormones. These negative effects are thought to be unavoidable by-products of sustained activation of the stress response, but the details remain unclear. A comparative perspective may help in understanding chronic stress. We exposed crickets (Gryllus texensis) to a mock predator. A single exposure to a mock predator induced a transient increase in the hemolymph (blood) concentration of the insect stress neurohormone, octopamine. Repeated exposure to the mock predator increased basal levels of octopamine, similar to the effects of chronic stress on the basal levels of vertebrate stress hormones. This study is the first to report an increase in the basal levels of an invertebrate stress hormone in response to repeated flight-or-fight stress. Chronic stress reduced weight gain, and decreased feeding and enhanced weight loss after food deprivation in adult female crickets. However, chronic stress also increased the tendency of crickets to produce sustained flight. Therefore, this study supports the hypothesis that increasing basal levels of stress hormones may be a phylogenetically common response to chronically stressful conditions. It also demonstrates that chronic stress has both positive and negative effects in insects.     

The influence of parental behavior on vulnerability to nest predation in tropical thrushes of an Andean cloud forest

The Skutch hypothesis predicts that parental activity around the nest may attract the attention of predators and thus, in the tropics where predation pressure may be high, selection favors reduced parental activity. This hypothesis has been questioned by studies demonstrating that parents can decrease the risk of nest predation through nest defense. The link between parental activity and predation risk may be further confounded by nest site characteristics. We examined the effects of parental behavior and nest site on clutch survival in two sympatric tropical thrushes (Myadestes ralloides and Turdus leucops). We compared survival rates of clutches in three treatments: 1) natural nests at the incubation stage, 2) unattended nests (un‐manipulated nests of the same species, with clutches unattended by parents), and 3) exposed clutches (eggs exposed in unconcealed positions, unprotected by the nest). Parental activity had a positive effect on clutch survival, which was revealed by significantly higher survival rate of clutches in attended nests compared to unattended nests. The effect of nest site was less clear: clutches in unattended natural nests survived better than clutches in exposed sites selected by humans, but results were insignificant. We propose that parent birds can exclude a group of opportunistic predators, that are able to destroy unattended clutches. Nest site characteristics may be less important in determining clutch survival in the tropics, where predator guilds are more diverse, making completely safe sites difficult to find. Our results challenge Skutch's hypothesis and point to the need for more data from tropical latitudes.     

Food stress and predator-induced stress shape developmental performance in a damselfly

I studied effects of stress factors like food shortage, non-lethal predator presence and autotomy on survival and larval performance (growth rate, development rate and developmental stability) of larvae of the damselfly Lestes sponsa. In a laboratory experiment, larvae were raised during their last two instars at two food levels (high or low) crossed with two levels of autotomy (caudal lamellae present or absent). These treatments were nested within three levels of predation risk (Aeshna cyanea absent, Chironomus-fed caged Aeshna or Lestes-fed caged Aeshna). The diet of the predator had no effects. The low food level and the presence of Aeshna independently increased mortality rates of L. sponsa larvae. The low food level, presence of a caged Aeshna and autotomy all independently reduced growth rate (mass and body size at day 40) and wing size at emergence, and the first two stress factors also reduced development rate. Regardless of predator presence and autotomy, all damselfly larvae consumed the food available. This indicated that the predator-induced stress effects were not due to reduced food uptake, but probably reflected lowered assimilation efficiency and/or a higher metabolic rate. Besides a low food level, the presence of caged Aeshna predator larvae and autotomy also increased hind wing asymmetry. This result demonstrated that predator-induced stress may reduce developmental stability in the prey.     

Day vs. night predation on artificial caterpillars in primary rainforest habitats – an experimental approach

The influence of natural enemies has led to the evolution of various predator avoidance strategies in herbivorous insects. Many caterpillars are exclusively active at night and rest during the day. It is widely assumed that nocturnal activity in caterpillars reduces their risk of falling prey to their natural enemies. To test this hypothesis, we compared predation pressure between day and night in tree‐fall gaps and closed‐canopy forest sites in an Amazonian primary lowland rainforest. Artificial clay caterpillars, showing camouflaged colouration (green), were exposed as potential prey to a natural predator community. Attacks were significantly more frequent during daytime and were reduced by about a quarter at night in tree‐fall gaps, and by a third in closed‐canopy forest sites. This supports the idea of time‐dependent activity in caterpillars as an antipredatory adaptation. Further, independent of the time of day, predation pressure on caterpillars was significantly higher in tree‐fall gaps compared to closed‐canopy forest habitats. Nearly all predation events were caused by arthropods, whereas birds played a negligible role. Across both habitat types and time scales, ants acted as major predator group, emphasising their important role in population control of herbivorous insects in lowland rainforest ecosystems. This is the first experimental study using artificial caterpillars to examine whether time‐scheduling of exposition might influence predation risk amongst undefended, solitary, free‐living lepidopteran larvae.     

Experimental evidence for alternative stable equilibria in a benthic pond food web

Both local and initial conditions have been implicated in causing variation in the strengths of predator effects among natural communities. In this study, I performed a controlled mesocosm experiment using two common snails, Physella gyrina and Helisoma trivolvis, and their insect predator, Belostoma flumineum, to explicitly quantify and understand the causes of previously observed variation in food web interactions in natural ecosystems. The results from a controlled mesocosm experiment showed that: (1) at low productivity, snails were dominated by small‐vulnerable species (P. gyrina), predator effects were strong and predator effects caused a trophic cascade extending to producers; (2) at high productivity, snails were dominated by large‐invulnerable species (H. trivolvis), predator effects were weak and there was no trophic cascade to producers; (3) at intermediate productivity, alternative stable equilibria were implicated, such that depending on initial conditions, snails were dominated by either small‐vulnerable or large‐invulnerable species and predator effects were either strong or weak. Thus, this study represents one of the first to quantify how variation in food web structure can result from the local environment, initial conditions and their interaction.     

Risk taking by singing males

The distance at which an individual flees from a potential predatorrepresents a measure of risk taking. If individuals are engagedin another activity that might affect fitness, trade-offs betweenthe fitness benefits of flight and the other activity shoulddetermine the nearest distance of approach by a predator. Ina comparative analysis of birds, flight distance representeda reliable measure of risk of predation by the sparrowhawk Accipiternisus that increased with decreasing flight distance acrossspecies. To test the hypothesis that singing males adjustedtheir risk taking to the costs and benefits of early flight,we compared the flight distance of singing and nonsinging birdsto an approaching human observing with a binocular. Singingbirds on average fled at a greater distance than nonsingingbirds, implying that singing birds took small risks. We useda standardized measure of difference in flight distance betweensinging and nonsinging individuals to investigate factors affectinginterspecific variation in risk taking. Species that used moreexposed song posts (sites used for singing) took smaller risksthan species with less exposed song posts. Species that sufferedfrom higher levels of parasitism as reflected by the prevalenceof Plasmodium, but not by 3 other genera of blood parasites,took greater risks during singing compared with nonsinging activities.Likewise, species with high circulating levels of natural antibodies,and hence a history of natural selection caused by bacteriatook relatively greater risks during singing than species withfew natural antibodies. These findings suggest that risks takenby singing birds have been molded by natural and sexual selection,and that risk taking represents a compromise between the costsand benefits of flight from a potential predator.     

Fecal corticosterone, body mass, and caching rates of Carolina chickadees (Poecile carolinensis) from disturbed and undisturbed sites

We tested for hormonal and behavioral differences between Carolina chickadees (Poecile carolinensis) taken from a disturbed (recently logged) forest, an undisturbed forest, or a residential site. We measured fecal corticosterone and body mass levels in the field, and fecal corticosterone, body mass, and caching behavior in an aviary experiment. In the field, birds from the disturbed forest exhibited significantly higher fecal corticosterone levels than birds from either the undisturbed forest or from the residential site. Birds from the disturbed forest also exhibited lower body mass than those from the undisturbed forest but higher body mass than those from the residential site. Our aviary results suggest that these physiological differences between field sites are the result of short-term responses to ecological factors: neither body mass nor fecal corticosterone levels varied between birds captured at different sites. Aviary sample sizes were sufficient to detect seasonal variation in fecal corticosterone (lowest in summer), body mass (highest in spring), and rate of gain in body mass (highest in winter). Under "closed-economy" aviary conditions (all food available from a feeder in the aviary), there were no site differences in the percent of seeds taken from the feeder that were cached. However, under "open-economy" conditions (food occasionally available ad libitum), significantly fewer seeds were cached by birds from the disturbed forest compared to the undisturbed or residential sites. On average, there was only a two-fold difference in population levels of fecal corticosterone. This difference is about the same as an increase in fecal corticosterone induced by a 2-h increase in food deprivation and cannot be considered to be an acute stress response to disturbance.     

How avian nest site selection responds to predation risk: testing an 'adaptive peak hypothesis'

1. Nest predation limits avian fitness, so birds should favour nest sites that minimize predation risk. Nevertheless, preferred nest microhabitat features are often uncorrelated with apparent variation in predation rates. 2. This lack of congruence between theory-based expectation and empirical data may arise when birds already occupy 'adaptive peaks'. If birds nest exclusively in low-predation microhabitats, microhabitat and nest predation may no longer be correlated even though predation ultimately shaped microhabitat selection. 3. This 'adaptive peak hypothesis' was tested for a population of Yellow Warblers (Dendroica petechia) focusing on two nest microhabitat features: concealment and height. Experimental nests measured relative predation risk both within and outside the microhabitat range typically occupied by natural nests to examine whether nest site choices made by birds restricted our ability to detect microhabitat effects on predation. 4. Within the natural range (30-80% concealment, >75 cm height), microhabitat-predation relationships were weak and inconsistent, and similar for experimental and natural nests. Over an extended range, however, experimental predation rates were elevated in exposed sites (<30% concealed), indicating a concealment-related 'adaptive plateau'. 5. Clay egg bite data revealed a concealment effect on avian predators, and the abundance of one avian predator group correlated with nest concealment among years, suggesting these predators may cue birds to modulate nest concealment choices. 6. This study demonstrates how avian responses to predation pressure can obscure the adaptive significance of nest site selection, so predation influences may be more important than apparent from published data.     

Supplementary feeding increases Common Buzzard Buteo buteo productivity but only in poor‐quality habitat

Temporal heterogeneity in the effects of food supply during the breeding season on the productivity of the Common Buzzard Buteo buteo was investigated in a supplementary feeding experiment. Pairs were fed artificially (1) before egg‐laying, (2) after chicks hatched and (3) continuously throughout the season, and compared with (4) unfed controls. Pairs fed before egg‐laying had marginally larger clutches than those not fed, but lay date, egg volume and weight, brood size and hatching success were unaffected. Territorial quality had far greater effects, with pairs nesting in low‐quality habitats (bog, scrub and semi‐natural grassland) laying later and having lower hatching success, smaller broods and fewer fledglings than those in more productive agricultural landscapes. Supplementary feeding after egg hatching neutralized the negative effect of poor habitat, resulting in fed birds having significantly more fledglings. This study emphasizes the importance of food availability when provisioning chicks in suboptimal habitats and has implications for the success of diversionary feeding in reducing game losses to Buzzards.     

Distress Calls of Birds in a Neotropical Cloud Forest1

Distress calls are loud, harsh calls given by some species of birds when they are captured by a predator or handled by humans. We recorded the frequency of distress calls and struggling behavior in 40 species of birds captured in mist nets during the dry season in a Costa Rica cloud forest. We tested the following hypotheses proposed to explain the function of distress calls: (1) calling for help from kin or reciprocal altruists; (2) warning kin; (3) eliciting mobbing behavior; (4) startling the predator; and (5) distracting the predator through attraction of additional predators. Our results did not support the calling‐for‐help, warning kin, or mobbing hypotheses. Indeed, genera that regularly occurred with kin or in flocks were not more likely to call than non‐flocking genera. There was no relationship between calling frequency and struggling behavior as predicted by the predator startle hypothesis. Genera of larger birds tended to call more than smaller birds, providing some support for both the predator distraction hypothesis and predator startle hypotheses. Calls of higher amplitude may be more effective in startling the predator. Distress calls of larger birds may also travel greater distances than those of smaller birds, supporting the predator manipulation hypothesis, but this requires further testing.     

Comparing food limitation among three stages of nesting: supplementation experiments with the burrowing owl

Food availability is an important limiting factor for avian reproduction. In altricial birds, food limitation is assumed to be more severe during the nestling stage than during laying or incubation, but this has yet to be adequately tested. Using food‐supplementation experiments over a 5‐year period, we determined the degree and timing of food limitation for burrowing owls (Athene cunicularia) breeding in Canada. Burrowing owls are an endangered species and food limitation during the nestling stage could influence reproductive performance of this species at the northern extent of their range. Supplemented pairs fledged on average 47% more owlets than unfed pairs, except during a year when natural food was not limiting (i.e., a prey irruption year). The difference in fledgling production resulted from high nestling mortality in unfed broods, with 96% of all nestling deaths being attributed to food shortage. Supplemental feeding during the nestling period also increased fledgling structural size. Pairs fed from the start of laying produced the same number of hatchlings as pairs that received no supplemental food before hatch. Furthermore, pairs supplemented from egg laying to fledging and pairs supplemented during the nestling period alone had the same patterns of nestling survival, equal numbers of fledglings, and similar fledgling mass and structural size. Our results provide empirical support for the hypothesis that the nestling period is the most food‐limited phase of the breeding cycle. The experimental design we introduce here could be used with other altricial species to examine how the timing of food limitation differs among birds with a variety of life‐history strategies. For burrowing owls, and other species with similar life histories, long‐term, large‐scale, and appropriately timed habitat management increasing prey abundance or availability is critical for conservation.     

Pre- and post-hatching effects of corticosterone treatment on behavior of the domestic chick

We investigated the effect of 60 ìg of corticosterone administered to domestic chicks either before or after hatching on the behavioral response to isolation in a novel arena and performance in a task involving the simultaneous identification of food and detection of a predator (overhead silhouette of a hawk moving overhead). Following release into a novel arena, chicks treated with corticosterone at 18 days of incubation emitted more distress vocalizations. In contrast, no difference in the number of vocalizations was found between chicks treated with corticosterone at day 1 post-hatching and controls. Behavior in the home cages was generally similar across treatments, though chicks treated with corticosterone at 18 days of incubation slept more than control chicks. While searching for grain against a background of pebbles, chicks treated with corticosterone at embryonic day 18, but not chicks treated on day 1 post-hatching, took longer to detect the overhead image of a predator than did controls. Corticosterone treatment at both ages increased the rate of pecking at grains and pebbles. Our findings support work on other birds indicating that corticosterone treatment during incubation influences stress reactivity. The impairment in predator detection in chicks treated with corticosterone on day 18 of incubation appears to be caused by the known effects of corticosterone treatment at this age in preventing the development of lateralization of the thalamofugal visual projections. This further supports the hypothesis that brain lateralization provides an advantage in performing more than one task simultaneously.     

Winter feeding of birds increases productivity in the subsequent breeding season

Supplementary food given to birds can have contemporary effects by reducing the risk of starvation, increasing survival and altering movements and reproductive performance. There is, however, a widely held perception that birds benefit from extra food over winter, but that it is better that they 'look after themselves' during breeding. Here we describe a landscape-scale experiment showing for the first time that the effects of increasing food availability only during the winter can be carried over to the subsequent breeding season. Even though food supplementation stopped six weeks prior to breeding, birds living on sites provisioned over winter had advanced laying dates and increased fledging success compared with birds living on unprovisioned sites. Thus, supplemental feeding of wild birds during winter, in a manner mimicking householders provisioning in gardens and backyards, has the potential to alter bird population dynamics by altering future reproductive performance. With levels of bird feeding by the public continuing to increase, the impacts of this additional food supply on wild bird populations may be considerable.     

Inactivation of Campylobacter jejuni by high hydrostatic pressure

AIMS: To investigate the response of Campylobacter jejuni ATCC 35919 and 35921 to high pressure processing (HPP) while suspended in microbiological media and various food systems. METHODS AND RESULTS: Campylobacter jejuni 35919 and 35921 were subjected to 10-min pressure treatments between 100 and 400 MPa at 25 degrees C suspended in Bolton broth, phosphate buffer (0.2 m, pH 7.3), ultra-high temperature (UHT) whole milk, UHT skim milk, soya milk and chicken pureé. The survivability of C. jejuni was further investigated by inoculated pack studies. HPP at 300-325 MPa for 10 min at 25 degrees C was sufficient to reduce viable numbers of both strains to below detectable levels when cells were pressurized in Bolton broth or phosphate buffer. All food products examined offered a protective effect in that an additional 50-75 MPa was required to achieve similar levels of inactivation when compared with broth and buffer. Inoculated pack studies showed that the survivability of C. jejuni following pressurization improved with decreasing post-treatment storage temperature. SIGNIFICANCE AND IMPACT OF THE STUDY: These data demonstrated that HPP at levels of 相似文献