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Probability of death of birds at different daily predation risk patterns (open circles constant risk of predation, open diamonds risk of predation decreases from morning to evening, open squares risk of predation increases from morning to evening, open triangles risk of predation is highest at midday and lowest in the morning and in the evening, filled circles risk of predation is highest in the morning and in the evening and lowest during midday) at three levels of variance in foraging success
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Accumulating and maintaining sufficient energy reserves is critical for winter survival of birds. Because high fat levels are assumed to be associated with higher risk of predation, birds have been hypothesized to regulate their body mass as a trade-off between risk of starvation and risk of predation. Theoretical models of energy management in bir...
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Context 1
... is generally predicted to peak in the after- noon (Fig. 4), although the rate of retrieval is higher for decreasing predation risk than for the increasing or con- stant predation risk schedules. Mean daily probability of death (from both starvation and predation) for decreasing and constant daily risk of predation is predicted to be similar (Fig. ...
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... daily probability of death should be lower for birds with daily predation risk increasing throughout the day compared with birds modeled with constant daily risk of predation (Fig. 5). Thus, predation costs imposed on morning foraging (our "decreasing predation risk sce- nario") have stronger fitness consequences than preda- tion costs on evening foraging (our "increasing predation risk scenario"). This prediction is not surprising because when foraging success is stochastic, birds try to gain most fat reserves in ...
Context 3
... predation risk is non-linear, the probability of death falls between the two linear patterns of predation (Fig. 5). When risk of predation is highest at midday, probability of death is similar to one modeled with con- stant risk of predation or with risk of predation decreas- ing from morning to evening. When predation risk is highest in the morning and in the evening, probability of death is somewhat lower, although not as low as when predation ...
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Citations
... When experiencing a rise in temperature, the wheatears indeed dropped their amount of migratory restlessness (table 4 and figure 5), and increased their energy stores accordingly (table 2 and figure 3) despite the not significantly affected food intake (electronic supplementary material, table S2 and figures S6 and S7). While carrying surplus energy is costly in terms of energy expenditure [52] and a reduced escape performance [53], it is also beneficial because it prolongs the total flight duration without accumulating further energy, minimizes the risk of starvation [54] and increases, for instance, the time available for anti-predator behaviour [27], and is therefore often observed in wild migratory birds [4]. As such, our experimental results provide causal evidence for a large body of correlative studies and the prediction that a temperature rise in combination with favourable feeding conditions prolongs stopover duration and is a beneficial strategy in autumn. ...
The decision-making process of migrating birds at stopover sites is a
complex interplay of the innate migration program and both intrinsic and extrinsic factors. While it is well studied how variation in precipitation, wind and air pressure influence this process, there is less evidence of the effects of temperature changes on the departure decision. Thus, we lack knowledge on how the predicted changes due to global climate change in temperature alone may affect the decision-making process during migration. Aiming to fill parts of this gap, we conducted a proof-of-concept study by manipulating the ambient temperature of temporarily confined wildcaught migrant songbirds under constant feeding conditions. In spring, departure probability increased with a 20°C rise in temperature for both a medium-distance migrant (European robin, Erithacus rubecula) and a longdistance migrant (northern wheatear, Oenanthe oenanthe), and in autumn, departure probabilities of the long-distance migrant both decreased with a 20°C rise and increased with a 20°C drop. Consequently, the temperature is an important departure cue influencing the decision-making process of migrating songbirds. Incorporating causal relationships between changes in temperature and departure probability in migration models could substantially
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... Alternatively, birds could be compensating through other (e.g., behavioral or physiological) means to reduce their sensitivity to extreme weather (Huey et al. 2012, Latimer et al. 2018) while simultaneously minimizing their risk of predation (Lima 1986, Houston andMcNamara 2013). For example, food-caching birds, like black-capped chickadees, may rely more heavily on cached food stores to minimize the amount of fat reserves needed to be carried Houston 1990, Pravosudov andLucas 2001), and thus, alter the relationship between body condition and survival. Last, as the winters in our study were two of the coldest winters of the past 30 yr, temperatures may have been so severe that they impacted all individuals similarly, regardless of the level of fat reserves carried. ...
Projected increases in the variability of both temperature and precipitation will result in the greater likelihood and magnitude of extreme weather (e.g., cold snaps, droughts, heat waves) with potential implications for animal populations. Despite the ecological consequences of extreme weather, there are several challenges in identifying extreme events and measuring their influence on key demographic processes in free‐living animals. First, there is often a mismatch between the spatial and/or temporal resolution of biological and climate data that could hinder our ability to draw accurate inferences about how species and populations respond to extreme events. Second, there are multiple approaches for identifying an extreme event ranging from statistical definitions (e.g., standardized deviates) to species‐specific biological thresholds. Lastly, the impacts of extreme weather on species can vary as a function of differences in exposure and intrinsic sensitivity to climate variability. In the Northern Hemisphere, rapid warming has contributed to a “wobblier” jet stream that promotes the higher likelihood of cold Arctic air moving southward and leading to more extreme winter conditions. Due to these conditions, the Upper Midwest experienced two of the coldest winters in the past 35 yr during 2014 and 2015. We combined radiofrequency identification technologies with fine‐scale weather data and standard capture–mark–recapture analyses to estimate weekly and overwinter survival rates of a common winter passerine, the Black‐capped Chickadee (Poecile atricapillus), in a near continuous fashion. Using both statistical and biological definitions of weather extremes, we found that declining ambient temperatures reduced survival (despite the presence of favorable microclimates), and that biologically defined thresholds of extreme weather were better at explaining variation in survival than statistical ones. Moreover, habitat fragmentation interacted with temperature to modify the exposure of birds to extreme weather with survival consequences, but sensitivity, as measured by body condition, did not appear to play a significant role. These results provide a novel contribution to the understanding of how extreme weather may interact with local‐ and landscape features to influence the demography of species and populations, and suggest potential opportunities for climate‐change adaptation in human‐dominated landscapes.
... For almost 40 years, Professor Thomas W. Sherry, at Tulane University since 1989, has contributed significantly to ornithology, ecol ogy, and conservation. Feeding be hav ior, resource partitioning, and diet specialization, particularly in resident tropical birds (Sherry 1984(Sherry , 1990 Johnson et al. 2006, Cooper et al. 2015 fast as they can, storing it in their crops or caching it (above), and pro cessing it later under protective cover (Pravosudov and Lucas 2001). Studies have also shown that storing energy in the form of fat could allow birds to operate without hav ing to sacrifice predator avoidance, but too much fat could increase predation risk by impairing their flight capabilities (reviewed by Bonter et al. 2013). ...
... Studies have also shown that storing energy in the form of fat could allow birds to operate without hav ing to sacrifice predator avoidance, but too much fat could increase predation risk by impairing their flight capabilities (reviewed by Bonter et al. 2013). Other studies have shown that birds minimize predation risk by foraging at lower risk times, or when the weather conditions hinder detection, or by selecting microhabitats where predators are less common (reviewed by Lima and Dill 1990, Pravosudov and Lucas 2001, McCabe and Olsen 2015. ...
... However, researchers have assumed constant predation risk throughout the day (Bonter et al. 2013) and constant background levels of predation risk. Other models predict a bimodal foraging pattern to balance predation and starvation risk (McNamara et al. 1994, Pravosudov andLucas 2001) implying that birds display 2 peaks in foraging activity, 1 early in the morning and 1 late in the day to replenish energy reserves (McNamara et al. 1994) while being inactive between peak foraging times to limit exposure to predators. Our results suggest increased human disturbance shifted foraging patterns to a bimodal pattern but decreased the overall area and duration of foraging to limit exposure levels. ...
Prey species must consistently balance the need for resource acquisition with the threat of predation. This balance is particularly true for gallinaceous birds, such as the northern bobwhite (Colinus virginianus), which are ground foragers and are often exposed to increased predation risk compared to arboreal foragers. We studied how bobwhites might mitigate the threat of human hunting pressure by altering their foraging strategy. We directly monitored hunting encounters with bobwhites, during October 2014-March 2015, and collected daily movement paths (n ¼ 514) using radio-telemetry. We performed first-passage time analysis to infer foraging behavior by calculating bout frequency, area, duration, and timing. We found bobwhites mitigated exposure to human hunters by increasing foraging frequency coupled with a decrease in duration (15.4%) and area (7.1%) in response to hunting pressure. We observed a temporal shift in foraging away from peak hunting hours by 30 minutes when birds were recently exposed to a discharged firearm. Our results imply that hunting game species can disrupt timing of foraging and therefore influence allocation to competing activities such as anti-predator vigilance. We propose implementing a dynamic harvest management regime that distributes hunting activity temporally and spatially to mitigate high hunting pressure and reduce behavioral effects on bobwhites. Careful planning of hunting activity should reduce its additive effects on natural mortality while improving hunter satisfaction. Ó 2018 The Wildlife Society.
... The basal metabolic rate (BMR) of a Clark's nutcracker is 2.40 kJ per time step (690.91 kJ * 300 s/86400 s). Pravosudov and Lucas (2001) estimated the metabolic costs of different activities for food-caching passerines as follows: foraging/consumption − 8 * BMR (19.20 kJ); resting − 1.95 * BMR (4.68 kJ); and night resting − 1 * BMR (2.40 kJ). In this ABM, costs of activity were set and an agent loses energy in accordance with these values. ...
While much is known about the relationship between Clark’s nutcracker and whitebark pine, information on nutcracker energetic behavioural strategies − the driving factors behind nutcracker emigration − and the impact of nutcracker behaviour on whitebark pine communities remain uncertain. To investigate nutcracker energetic behaviour, we developed a spatially explicit agent-based model (ABM) to simulate the underlying behavioural mechanisms nutcrackers are most likely to employ during foraging in the South Cascades near Mt. Rainier, Washington. The ABM is comprised of cognitive nutcracker agents possessing memory and decision-making heuristics that act to optimize energy acquisition and loss. Environmental data layers for elevation and basal area of tree species were used to represent the landscape in terms of habitat and energy resources. We employed the evaludation approach for an organized sequence of model development and analysis, including: data evaluation, conceptual model evaluation, implementation, verification, model output verification (calibration consisting of comparison of parameters informed by nutcracker ecology to real-world empirical values; pattern-oriented modeling − POM), model analysis (sensitivity of model to changes in parameters and processes), and model output corroboration (use of POM to compare model output to real-world patterns from empirical investigations of nutcracker ecology, independent of calibration). Simulations were conducted on alternative nutcracker behavioural-energetic mechanism strategies by assigning different fitness-maximizing goals to agents. We found that an integrated energetic requirement (IER) mechanism, which includes both the short-term and long-term energetic needs of nutcracker agents to be the best-fit scenario. Our results affirm previous research that nutcrackers are responsive to changes in their energetic environment, and that they are capable of projecting energy budgets well into the future. The development of this ABM provides a basis for future research, such as a means to assess the driving conditions necessary for nutcrackers when choosing between a resident and emigrant strategy and as a planning tool to model nutcracker responses to potential landscape changes, which may facilitate long-term WBP conservation.
... Furthermore, the increase in predation risk was demonstrated to suppress the intense effect of fasting on nocturnal hypothermia in pigeons, which is considered a remarkable strategy of energy conservation in birds [22]. Together with results of dynamic models of short-term energy management in birds, these data suggest that the regulation of energy balance may be a function of a trade-off between the risk of predation and the threat of famine in avian species (e.g., [23]). ...
Changes in body temperature are significant physiological consequences of stressful stimuli in mammals and birds. Pigeons (Columba livia) prosper in (potentially) stressful urban environments and are common subjects in neurobehavioral studies; however, the thermal responses to stress stimuli by pigeons are poorly known. Here, we describe acute changes in the telemetrically recorded celomatic (core) temperature (Tc) in pigeons given a variety of potentially stressful stimuli, including transfer to a novel cage (ExC) leading to visual isolation from conspecifics, the presence of the experimenter (ExpR), gentle handling (H), sham intracelomatic injections (SI), and the induction of the tonic immobility (TI) response. Transfer to the ExC cage provoked short-lived hyperthermia (10-20min) followed by a long-lasting and substantial decrease in Tc, which returned to baseline levels 2h after the start of the test. After a 2-hour stay in the ExC, the other potentially stressful stimuli evoked only weak, marginally significant hyperthermic (ExpR, IT) or hypothermic (SI) responses. Stimuli delivered 26h after transfer to the ExC induced definite and intense increases in Tc (ExpR, H) or hypothermic responses (SI).These Tc changes appear to be unrelated to modifications in general activity (as measured via telemetrically recorded actimetric data). Repeated testing failed to affect the hypothermic responses to the transference to the ExC, even after nine trials and at 1- or 8-day intervals, suggesting that the social (visual) isolation from conspecifics may be a strong and poorly controllable stimulus in this species. The present data indicated that stress-induced changes in Tc may be a consistent and reliable physiological parameter of stress but that they may also show stressor type-, direction- and species-specific attributes.
Copyright © 2014. Published by Elsevier Inc.
... This would be particularly important for individuals employing a body-mass delay strategy; rather than exploiting known patches in the morning, birds could be searching (either socially or asocially) for new resource locations while they are light or when predation risk is low. Models of caching behaviour suggest high rates of caching in the morning with high retrieval rates late in afternoon [8]. ...
... We predicted that if individuals are shifting strategies from exploration to exploitation, we should observe a non-random pattern of within day-discovery, with higher probabilities of discovering food earlier in the day. Given the presence of multiple species in the population, we then tested for species-level differences, testing the prediction that caching species should be more likely to discover novel food sources earlier given their need to accumulate food earlier than non-cachers [8]. ...
Animals need to manage the combined risks of predation and starvation in order to survive. Theoretical and empirical studies have shown that individuals can reduce predation risk by delaying feeding (and hence fat storage) until late afternoon. However, little is known about how individuals manage the opposing pressures of resource uncertainty and predation risks. We suggest that individuals should follow a two-part strategy: prioritizing the discovery of food early in the day and exploiting the best patch late in the day. Using automated data loggers, we tested whether a temporal component exists in the discovery of novel foraging locations by individuals in a mixed-species foraging guild. We found that food deployed in the morning was discovered significantly more often than food deployed in the afternoon. Based on the diurnal activity patterns in this population, overall rates of new arrivals were also significantly higher than expected in the morning and significantly lower than expected in the afternoon. These results align with our predictions of a shift from patch discovery to exploitation over the course of the day.
... Our use of PITs and RFID-enabled bird feeders to quantify the feeding activity of free-living birds has generated a heretofore unprecedented dataset on feeding behaviour by individuals. The long-standing bimodal foraging hypothesis, proposed by models of optimal foraging behaviour for birds exposed to the risk of predation [4,5], was not supported by the activity patterns of birds in our population. Rather, we showed that birds fed relatively continuously throughout the day and terminated feeding abruptly as sunset approached. ...
Daily patterns in the foraging behaviour of birds are assumed to balance the
counteracting risks of predation and starvation. Predation risks are a function
of the influence of weight on flight performance and foraging behaviours that
may expose individuals to predators. Although recent research sheds light on
daily patterns in weight gain, little data exist on daily foraging routines in
free-living birds. In order to test the predictions of various hypotheses
about daily patterns of foraging, we quantified the activity of four species
of passerines in winter using radio-frequency identification receivers built
into supplemental feeding stations. From records of 472 368 feeder visits by
tagged birds, we found that birds generally started to feed before sunrise
and continued to forage at a steady to increasing rate throughout the day.
Foraging in most species terminated well before sunset, suggesting their
required level of energy reserves was being reached before the end of the
day. These results support the risk-spreading theorem over a long-standing
hypothesis predicting bimodality in foraging behaviour purportedly driven
by a trade-off between the risks of starvation and predation. Given the
increased energetic demands experienced by birds during colder weather,
our results suggest that birds’ perceptions of risk are biased towards
starvation avoidance in winter.
... It is perhaps surprising that this time of day effect was linear in the Siberian jays, since a range of different curvilinear diurnal mass gain trajectories can be predicted (Brodin 2000). However, linear (or near-linear) increases in mass over the day have also been predicted and found in other studies (Ekman & Lilliendahl 1993;Brodin 2000;Pravosudov & Lucas 2001;Macleod et al. 2005b), and so this might well have been the case here. Alternatively, the relatively small sample sizes and limited range of measurements for all periods of all days could mean that we lacked the statistical power required to detect any Body mass (g) Figure 3. ...
A profusion of theoretical and empirical studies has successfully explored the issue of adaptive management of body mass by small birds threatened with both starvation and predation. In addition to diurnal body mass cycles, body mass tends to increase with either poorer mean conditions or more variable conditions, such as those often experienced during winter. In many species, individual dominance status will affect access to food and predation risk, and is therefore predicted to influence patterns of optimal body mass further. We investigated body mass regulation via repeated measurements without capture in groups of Siberian jays, Perisoreus infaustus, during autumn. As predicted, body mass of individuals increased throughout the day and towards the winter and was higher during colder periods. Jay body mass was also correlated with wind chill conditions 23 h before. This makes sense since conditions 24 h earlier were a better predictor of current conditions than conditions either 12 or 48 h earlier. Dominant birds (i.e. breeders) that were large carried relatively lower fat reserves than large subordinate individuals. The opposite was true for morphologically small birds. Together this suggests tighter requirements for individual variation in mass for dominant breeders in these groups. Our findings in this food-hoarding corvid are in general agreement with models and results concerning much smaller birds.
... The relative importance of handling time as a factor influencing the decision to cache is yet to be resolved. Most models of caching behavior aiming to understand caching decisions have used stochastic dynamic programming (McNamara et al. 1990; Lucas and Walter 1991; Brodin and Clark 1997; Pravosudov and Lucas 2001 ). These models effectively determine how an optimal forager manages state dependencies , current versus future consumptions of food, and predation–starvation risk trade-offs. ...
Food caching is widespread among several animal species. Few studies have proposed that handling time should affect the evolution of caching behavior, especially under foraging time constraints. Nevertheless, to date, there has been no analytical support to the ‘‘handling time hypothesis.’’ In the present article, we use an analytical model to show that caching behavior may evolve as the result of shorter handling time caching relative to eating. We evaluate caching behavior under 3 fitness objectives (or environmental scenarios): maximizing energy consumed, maximizing and balancing energy consumed, and maximizing energy consumed under risk of predation. Our analyses reveal that under all 3 fitness objectives, caching behavior can evolve when caching time is shorter than eating time, to allow the animal to free up search time during the period when food is plentiful and postpone time spent handling to the period when food is scarce and search time is less valuable. That effect may be called ‘‘search time reallocation,’’ and it is still prevalent even if food decays. Our model provides predictions that can be field tested,
adds to the debate of handling time and perishability hypotheses, and invites researchers to direct their focus toward understanding the evolutionary motives of caching behavior.
