Behavioural responses during feather replacement in house sparrows

Birds lose feathers, whether during molt or by accident, and replace them by processes that are energetically demanding. We hypothesized that house sparrows Passer domesticus biblicus use behavioral means to save energy when feathers are lost, and tested the general prediction that house sparrows growing new feathers adjust their behavior to minimize the energy costs of foraging and to increase net energy gain from their food. To test these predictions we divided 18 house sparrows into three groups: 1) plucked – house sparrows from which we plucked 15 flight feathers; 2) cut – house sparrows in which the same 15 feathers were cut off at the calamus below the barbs; and 3) control – unmanipulated house sparrows with plumage intact. We recorded both the quantity of seeds the house sparrows ate and the time they spent foraging from assay food patches. We found that ‘plucked’ sparrows growing new feathers adjust their foraging behavior by reducing their feeding time and the number of visits to a food patch. This allowed them to increase their patch harvest rate while maintaining a steady body mass.     

Greenhead ants Rhytidoponera metallica make trade‐offs between food temperature and food concentration

1. Foraging animals are often faced with foods that vary in several important attributes, some of which may be in conflict with one another. For ectothermic animals, food temperature can be an important characteristic, as the consumption of cold foods is metabolically costly. 2. Here, the effect of food temperature on food preferences in the green‐headed ant Rhytidoponera metallica (Smith, 1858) was investigated. The first aim of the study was to determine how food concentration (caloric value) and relative food temperature influenced colony‐level preferences. We found that, all else being equal, green‐headed ant colonies preferred warmer food solutions over colder solutions, and more concentrated food solutions over less concentrated ones. 3. Next, the question of whether green‐head ant colonies could make trade‐offs between temperature and food concentration was tested. It was found that ant colonies switched their preferences in favour of a colder food solution when the colder food solution was 10 times more concentrated than the warmer food solution. 4. These experiments show that temperature is an important characteristic shaping food preferences in ants. Moreover, we show that colonies can make trade‐offs between food concentration and food temperature.     

Habitat choice in shoals of roach as a function of water temperature and feeding rate

Temperature and food availability are two important factors which affect fish growth and therefore are expected to influence habitat choice in fish. In this study, shoals of 16 juvenile roach, Rutilus rutilus , were given a choice between two chambers that differed in temperature by 1·5°C or 3°C whereas food availability was the same in both chambers (ratio 1 : 1) or higher in the colder one (ratio 4 : 1). The number of fish in each chamber was recorded for 10 min each during a pre-feeding, feeding and post-feeding period. Roach generally preferred the warmer over the colder chamber during the pre-feeding periods. Temperature had a significant effect on the distribution of fish during all three time periods whereas food availability was a significant factor only during the feeding period. The important role of temperature was emphasized further by the fact that a relatively small difference in the temperature gradient of 1·5°C had a stronger effect on fish distribution than a four times higher feeding rate during the feeding period. The implications for growth rates of such short-term decision-making of roach are discussed.     

Energy budget during four successive bouts of lactation in striped hamsters exposed to decreases in ambient temperature

A prediction of the seasonal investment hypothesis is that overall energy investment needs to be greater for young being produced at colder temperatures. Then, that energy cost is lower as temperature becomes warmer. To evaluate this assumption, I performed a series of measures of food intake and reproductive output throughout four successive bouts of lactation in striped hamsters (Cricetulus barabensis) exposed to a constant warm temperature (Warm, 21°C) or exposed to consecutive decreases in ambient temperatures from warm to cold (Warm-Cold, 30-0°C). Warm hamsters showed similar asymptotic food intake, litter size and mass over the course of four successive bouts of lactation. Warm-Cold females consumed more food, but raised lighter litters during the third bout than first bout of lactation. Ambient temperatures had significant effects on energy budget and reproductive output, by which resting metabolic rate, nonshivering thermogenesis and activity of cytochrome c oxidase (EC 1.9.3.1) of brown adipose tissue were increased, but reproductive output was decreased with declines of temperatures. These findings suggest that a trade-off occurs between different components of energy expenditure during the successive course of four bouts of lactation. Seasonal hamsters decrease their reproductive output, but increase the energy spent on thermogenesis as the ambient temperature becomes colder. It may also indicate that temperature has a direct effect on metabolism, leading to an increase in overall energy expenditure at lower temperatures.     

Territorial defence of space and feeding sites by a plethodontid salamander

Two series of experiments were conducted, one in field enclosures and another in the laboratory, to test the hypothesis that the salamander Desmognathus monticola (family Plethodontidae) defends its refuges and feeding sites against conspecific intruders. When two identical cover sites were provided as refuges in the laboratory, residents and intruders occupied separate cover sites significantly more often than the same sites. Residents did not, however, show strong preference for the same site, nor did they consistently defend a specific site. When food supplements were provided consistently at the same cover sites in field enclosures, resident D. monticola occupied and defended the feeding sites significantly more frequently against intruders than the non-feeding cover sites. Individuals not receiving food supplements also excluded intruders from the occupied cover sites but did not defend a specific cover site. Residents in enclosures where no food supplements were provided were significantly more active at night, outside cover sites, than residents receiving food supplements. Individual D. monticola exhibit territoriality by excluding intruders from the refuges they occupy. Providing food supplements increases the site specificity of individuals and decreases the amount of time spent in nocturnal activity.     

Latitudinal compensation in oyster ciliary activity

1. Theories of latitudinal compensation predict that individuals living in colder temperature regimes should physiologically compensate for the slowing of standard physiological rates, owing to the relatively low temperature of their local environments, by increasing their metabolic rate in colder water temperatures relative to individuals living in warmer water temperature regimes.
2. This hypothesis was tested with oyster strains originally from geographically separated populations that were raised in a common environment for seven generations. The physiological parameter measured was ciliary activity across a temperature gradient.
3. Support for the latitudinal compensation hypothesis was found: the strain originally from the colder temperature regime had more active cilia at lower experimental temperatures than individuals originally from the warmer temperature regime. Ciliary activity of the more northern Long Island Sound oysters was significantly greater than activity in the more southern Delaware Bay oysters at temperatures of –1, 2 and 6 °C.
4. These results suggest that there is genetically based physiological differentiation between these populations of oysters consistent with the latitudinal compensation for local temperature regime.     

The effects of predation risk on the use of social foraging tactics

The effects of predation on the use of social foraging tactics, such as producing and scrounging, are poorly known in animals. On the one hand, recent theoretical models predict increased use of scrounging with increasing predation risk, when scroungers seeking feeding opportunities also have a higher chance of detecting predators. On the other hand, there may be no relation between tactic use and predation when antipredator vigilance is not compatible with scanning flockmates. We investigated experimentally the effects of predation risk on social foraging tactic use in tree sparrows, Passer montanus. We manipulated predation risk in the field by changing the distance between shelter and a feeder. Birds visited the feeder in smaller flocks, spent less time on it and were somewhat more vigilant far from shelter than close to it. Increased predation risk strongly affected the social foraging tactic used: birds used the scrounger tactic 30% more often far from cover than close to it. Between-flock variability in scrounging frequency was not related to the average vigilance level of the flock members, and within-flock variability in the use of scrounging was negatively related to the vigilance of birds. Our results suggest that in tree sparrows, the increased frequency of scrounging during high predation risk cannot simply be explained by an additional advantage of increasing antipredator vigilance. We propose alternative mechanisms (e.g. increased stochasticity in food supply, and that riskier places are used by individuals with lower reserves) that may explain increased scrounging when animals forage under high predation risk.     

Increasing temperature associated with increasing grilse proportion and smaller grilse size of Atlantic salmon

Effects of temperature on Atlantic salmon (Salmo salar) were analysed using Carlin tag recovery data (1985–2014), and mixed-stock catch data (smolt years from 2001 to 2012) in northern parts of the Baltic Sea. During warmer summers, the mean smolt length of the recaptured salmon tended to be smaller, and salmon were recaptured more frequently in feeding grounds closer to the home rivers in the Gulf of Bothnia, while colder summers were associated with more recaptures further south, in the Baltic Main Basin. Moreover, a warmer spring in the smolt year was associated with decreased weight of male grilses in mixed stock data. Further, warmer spring temperatures during the smolt year were associated with a higher proportion of one-sea-winter (1SW) males during the return migration in mixed stock data. These results suggest that the increasing global temperature may affect Atlantic salmon life history demographics.     

The feeding, growth, and energetics of two rocky intertidal predators (Pisaster ochraceus and Nucella canaliculata) under water temperatures simulating episodic upwelling

Although most upwelling regions are marked by strong fluctuations in water temperature, few studies have examined how episodic cold-water events affect the physiology and ecology of benthic marine invertebrates. I tested the hypothesis that upwelling-related variation in water temperature regulates the feeding, growth, and energetics of two rocky intertidal predators, the sea star Pisaster ochraceus (Brandt, 1835) and the whelk Nucella canaliculata (Duclos, 1832). Sea stars and whelks were maintained in laboratory tanks at a constant 9 °C, a constant 12 °C, and a treatment that simulated the Oregon coast upwelling regime by cycling between 14-day periods of 12 and 9 °C. Early in the experiments, sea stars and whelks held at 9 °C consumed about 30% fewer mussels (Mytilus trossulus) than those in warmer tanks. Despite lower consumption by whelks in colder tanks, 9 and 12 °C individuals attained the same final size. Similarly, sea stars in 9 °C tanks showed greater growth per gram of mussel tissue consumed than individuals held at 12 °C. These results suggest that reduced consumption under colder conditions was balanced by reduced metabolic costs. Moreover, there appeared to be an energetic advantage to living in the temperature regime characteristic of intermittent upwelling. Sea stars alternately exposed to 12 and 9 °C had a significantly higher growth rate, conversion efficiency, and storage of reserves in the pyloric caeca than individuals in the constant 12 °C tanks. Whelks maintained under fluctuating temperatures tended to grow faster than those held at constant 12 or 9 °C, although this trend was not statistically significant (p=0.069). These results suggest that benthic consumers experiencing cyclic temperatures may feed intensely during periods of warmer water while benefiting from reduced metabolic costs during cold-water intrusions. Because the fecundity of Pisaster and Nucella is a function of energy stored during the upwelling season, interannual variability in upwelling patterns could alter the reproductive output of these species.     

Paradox: increased blood perfusion to the face <Emphasis Type="BoldItalic">enhances</Emphasis> protection against frostbite while it <Emphasis Type="BoldItalic">lowers</Emphasis> wind chill equivalent temperatures

A model of facial heat exchange in cold and windy environments is presented. The tissue is depicted as a hollow cylinder and the model includes heat conduction and heat transport by blood circulation from the warmer core. A steady-state solution facilitating the estimation of wind chill equivalent temperature (WCET) as a function of the effective wind velocity, air temperature and blood perfusion rate was obtained. The results quantify and demonstrate the elevation of skin temperatures caused by increased flow of warmer blood from the inner core to the face. Elevated facial temperatures, while enhancing protection against frostbite and other cold-related injuries, also increase heat loss to the colder environment. Paradoxically, such elevated facial temperatures cause WCETs, as estimated by the prevailing definition, to attain lower rather than higher values, indicating, in fact, increased risk of frostbite. The results of this study should be useful in understanding and quantifying the effects of blood perfusion in protection against cold-related injuries. They should also be considered in the re-evaluation and re-formulation of the concept of wind chill, which has been a useful cold weather indicator for decades.     

Adaptation potential of the copepod Eurytemora affinis to a future warmer Baltic Sea

To predict effects of global change on zooplankton populations, it is important to understand how present species adapt to temperature and how they respond to stressors interacting with temperature. Here, we ask if the calanoid copepod Eurytemora affinis from the Baltic Sea can adapt to future climate warming. Populations were sampled at sites with different temperatures. Full sibling families were reared in the laboratory and used in two common garden experiments (a) populations crossed over three temperature treatments 12, 17, and 22.5°C and (b) populations crossed over temperature in interaction with salinity and algae of different food quality. Genetic correlations of the full siblings’ development time were not different from zero between 12°C and the two higher temperatures 17 and 22.5°C, but positively correlated between 17 and 22.5°C. Hence, a population at 12°C is unlikely to adapt to warmer temperature, while a population at ≥17°C can adapt to an even higher temperature, that is, 22.5°C. In agreement with the genetic correlations, the population from the warmest site of origin had comparably shorter development time at high temperature than the populations from colder sites, that is, a cogradient variation. The population with the shortest development time at 22.5°C had in comparison lower survival on low quality food, illustrating a cost of short development time. Our results suggest that populations from warmer environments can at present indirectly adapt to a future warmer Baltic Sea, whereas populations from colder areas show reduced adaptation potential to high temperatures, simply because they experience an environment that is too cold.     

Nocturnal feeding by Dark-bellied Brent Geese Branta bernicla bernicla

The occurrence and extent of nighttime feeding by Dark-bellied Brent Geese Branta bernicla bernicla on salt marshes adjacent to their tidal roost site were assessed on the north Norfolk coast using position-sensitive radio transmitters. Nine birds were monitored on 143 bird-nights, and feeding was recorded on 87. The frequency of feeding by night varied widely between individuals. The mean proportion of the night spent feeding for one bird was 19.7 ± 8%. Of this, 59% occurred within ± 1.5 h of high tide. Neither the proportion of the whole night spent feeding nor the intensity of feeding around high tide varied with the length of the night or with time after sunset at which high tide occurred. The extent of nocturnal feeding was also independent of the brightness and duration of moonlight. The birds fed for significantly longer on colder nights, and there was a significant positive relationship between the proportion of the night spent feeding and maximum temperature the preceding day. Analysis of daytime activity budgets on inland pastures showed that the proportion of time engaged in nonfeeding, energy-expensive activities was also positively related to maximum daytime temperature. Increases in the proportion of the night spent feeding after warmer days were achieved by increasing the period of time spent feeding on either side of the high tide, not by increasing feeding intensity at high tide. It is concluded that the geese compensate for increased energy expenditure during the day by increasing the extent to which they feed at night. Implications of increasing energy expenditure as a result of disturbance during the day are discussed.     

THE INFLUENCE OF THE CALIFORNIA MARINE LAYER ON BILL SIZE IN A GENERALIST SONGBIRD

The hypothesis is tested that birds in hotter and drier environments may have larger bills to increase the surface area for heat dissipation. California provides a climatic gradient to test the influence of climate on bill size. Much of California experiences dry warm/hot summers and coastal areas experience cooler summers than interior localities. Based on measurements from 1488 museum skins, song sparrows showed increasing body‐size‐corrected bill surface area from the coast to the interior and declining in the far eastern desert. As predicted by Newton's convective heat transfer equation, relative bill size increased monotonically with temperature, and then decreased where average high temperatures exceed body temperature. Of the variables considered, distance from coast, average high summer temperature, and potential evapotranspiration showed a strong quadratic association with bill size and rainfall had a weaker negative relationship. Song sparrows on larger, warmer islands also had larger bills. A subsample of radiographed specimens showed that skeletal bill size is also correlated with temperature, demonstrating that bill size differences are not a result of variation in growth and wear of keratin. Combined with recent thermographic studies of heat loss in song sparrow bills, these results support the hypothesis that bill size in California song sparrows is selected for heat dissipation.     

Ambient, productive and wind energy, and ocean extent predict global species richness of procellariiform seabirds

Aims Tests of the energy hypothesis for the large‐scale distribution of species richness have largely been concerned with the influence of two alternative forms of environmental energy, temperature and energy from primary productivity, both of which (at least in terrestrial systems) peak within the tropics. Taxa showing extra‐tropical diversity peaks present a potential challenge to the generality of species–energy theory. One such group are pelagic seabirds of the order Procellariiformes that show not only an extra‐tropical diversity peak but one confined to the Southern Ocean, hence a highly asymmetric one. They are distinct in being exceptionally adapted to take advantage of wind energy, which they may rely on for long‐distance ocean foraging for the patchy resources needed to meet their energetic needs. Wind represents a readily available source of kinetic energy, shows a strong latitudinal gradient, and has been largely omitted from species–energy theory. Moreover, maximal benefits of wind are likely to be afforded in areas of greatest available contiguous ocean extent. We compare the relative importance of wind speed, ocean productivity (chlorophyll concentration), air temperature and available ocean extent (distance) in explaining large‐scale global distribution of procellariiform species richness across the world's oceans. Location Global, oceanic. Methods Hierarchical partitioning, model selection, ordinary least squares (OLS) and spatial generalized least squares (GLS) regression. Results Hierarchical partitioning of non‐spatial regression models indicates that ocean distance is the most important predictor of procellariiform species richness followed by wind speed and then temperature. In contrast, that of spatial regression models indicates the roughly equal importance of ocean distance and temperature, followed by wind speed. Although contributing additional model fit, ocean productivity is consistently the weakest predictor. Best‐fit models include all four predictors and explain 67% of observed variation. The species–productivity relationship is negative overall, while the species–temperature relationship is hump‐shaped. In contrast, ocean distance and wind speed are positively associated with species richness. Conclusions Large‐scale procellariiform species richness distribution may represent a trade‐off in the use of different energy forms, being highest in Southern Ocean areas where productive energy and temperature are relatively low, but where available ocean foraging extent and wind energy required to utilize it are near‐maximal.     

A natural heating experiment: Phenotypic and genotypic responses of plant phenology to geothermal soil warming

Under global warming, the survival of many populations of sedentary organisms in seasonal environments will largely depend on their ability to cope with warming in situ by means of phenotypic plasticity or adaptive evolution. This is particularly true in high‐latitude environments, where current growing seasons are short, and expected temperature increases large. In such short‐growing season environments, the timing of growth and reproduction is critical to survival. Here, we use the unique setting provided by a natural geothermal soil warming gradient (Hengill geothermal area, Iceland) to study the response of Cerastium fontanum flowering phenology to temperature. We hypothesized that trait expression and phenotypic selection on flowering phenology are related to soil temperature, and tested the hypothesis that temperature‐driven differences in selection on phenology have resulted in genetic differentiation using a common garden experiment. In the field, phenology was related to soil temperature, with plants in warmer microsites flowering earlier than plants at colder microsites. In the common garden, plants responded to spring warming in a counter‐gradient fashion; plants originating from warmer microsites flowered relatively later than those originating from colder microsites. A likely explanation for this pattern is that plants from colder microsites have been selected to compensate for the shorter growing season by starting development at lower temperatures. However, in our study we did not find evidence of variation in phenotypic selection on phenology in relation to temperature, but selection consistently favoured early flowering. Our results show that soil temperature influences trait expression and suggest the existence of genetically based variation in flowering phenology leading to counter‐gradient local adaptation along a gradient of soil temperatures. An important implication of our results is that observed phenotypic responses of phenology to global warming might often be a combination of short‐term plastic responses and long‐term evolutionary responses, acting in different directions.     

Climatic severity and the response to temperature elevation of Arctic aphids

• 1 Theory suggests that any given rise in temperature resulting from climate change will have its greatest effect on high Arctic ecosystems where growing seasons are short and temperatures low.
• 2 A small temperature rise, similar to that predicted for the middle of the next century, has profound effects on a population of the high Arctic, Dryas-feeding aphid Acyrthosiphon svalbardicum on Spitsbergen (Strathdee et al. 1993a).
• 3 Here comparative experiments on a closely related Dryas-feeding species, A. brevicorne, at two contrasting sub-Arctic sites are described. Together with the results from Spitsbergen these sites represent two colder sites (high Arctic and upland sub-Arctic) and one warmer site (lowland sub-Arctic).
• 4 Differential responses in aphid population density and overwintering egg production to temperature elevation support the hypothesis that the ecological effects are greatest at sites with the most severe climates; however, there is no similar gradient in advancement of host plant phenology with warming.

     

Learning to Choose Among Social Foraging Strategies in Adult House Sparrows (Passer domesticus)

Social foragers may be regarded as being engaged in a producer–scrounger game in which they can search for food independently or join others who have discovered food. Research on the producer–scrounger game has focused mainly on the different factors influencing its evolutionarily stable strategy (ESS) solution, but very little is known about the actual mechanisms that shape players' decisions. Recent work has shown that early experience can affect producer–scrounger foraging tendencies in young house sparrows and that in nutmeg mannikins learning is involved in reaching the ESS. Here, we show that direct manipulation of the success rate experienced by adult sparrows when following others can change their strategy choice on the following day. We presented to live sparrows an experimental regime, where stuffed adult house sparrows in a feeding position were positioned on a foraging grid that included two reward regimes: a positive one, in which the stuffed models were placed near food, and a negative one, in which the models were placed away from food. There was a significant increase in joining behavior after the positive treatment (exhibited by 84% of the birds), but no change after the negative treatment. Further analysis demonstrated that sparrows more frequently used the strategy with which they were more successful (usually joining) and that differences in strategy use were correlated with differences in success. These results suggest that adult birds can monitor their success and learn to choose among social foraging strategies in the producer–scrounger game.     

Temperature-mediated coexistence in temperate forest ant communities

Patterns of ant species diversity are well documented and yet the mechanisms promoting species coexistence among communities are often elusive. Two emerging hypotheses that account for coexistence in ant communities are the discovery-dominance tradeoff and the dominance-thermal tolerance tradeoff. Here we used behavioural assays and community-level sampling from ant assemblages in the southern Appalachians, USA to test for the discovery-dominance and dominance-thermal tolerance tradeoffs. Species that were behaviorally dominant during interspecific interactions tended to forage in a narrow window of generally warmer temperatures, whereas subordinate species tended to forage in a wide range of temperatures, including colder temperatures. Species that foraged at lower temperature tended to be behaviourally subordinate, suggesting that a dominance-thermal tolerance tradeoff promotes coexistence in this system. Species richness was positively related to site average annual temperature and within-site variation in ground temperature, suggesting that temperature also shapes the structure of ant communities and regulates diversity. There was no relationship between the ability of a species to discover food resources and its behavioural dominance, contrary to the predictions of the discovery-dominance tradeoff hypothesis. In sum, our results show that temperature plays numerous roles in promoting regional coexistence in this system.     

Greater temperature sensitivity of plant phenology at colder sites: implications for convergence across northern latitudes

Warmer temperatures are accelerating the phenology of organisms around the world. Temperature sensitivity of phenology might be greater in colder, higher latitude sites than in warmer regions, in part because small changes in temperature constitute greater relative changes in thermal balance at colder sites. To test this hypothesis, we examined up to 20 years of phenology data for 47 tundra plant species at 18 high‐latitude sites along a climatic gradient. Across all species, the timing of leaf emergence and flowering was more sensitive to a given increase in summer temperature at colder than warmer high‐latitude locations. A similar pattern was seen over time for the flowering phenology of a widespread species, Cassiope tetragona. These are among the first results highlighting differential phenological responses of plants across a climatic gradient and suggest the possibility of convergence in flowering times and therefore an increase in gene flow across latitudes as the climate warms.     

Spatial heterogeneity in the effects of climate and density-dependence on dispersal in a house sparrow metapopulation

Dispersal plays a key role in the response of populations to climate change and habitat fragmentation. Here, we use data from a long-term metapopulation study of a non-migratory bird, the house sparrow (Passer domesticus), to examine the influence of increasing spring temperature and density-dependence on natal dispersal rates and how these relationships depend on spatial variation in habitat quality. The effects of spring temperature and population size on dispersal rate depended on the habitat quality. Dispersal rate increased with temperature and population size on poor-quality islands without farms, where house sparrows were more exposed to temporal fluctuations in weather conditions and food availability. By contrast, dispersal rate was independent of spring temperature and population size on high-quality islands with farms, where house sparrows had access to food and shelter all the year around. This illustrates large spatial heterogeneity within the metapopulation in how population density and environmental fluctuations affect the dispersal process.