Fattening strategies of wintering great tits support the optimal body mass hypothesis under conditions of extremely low ambient temperature (original) (raw)
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Strategy and constraint in the winter fattening response to temperature in the great tit Parus major
Journal of Animal Ecology, 2002
1. For many small birds at temperate latitudes, the low temperatures and long nights of winter are associated with an increased risk of starvation. Birds such as the great tit Parus major L. face this by increasing their fat reserves. Theoretical, correlative and experimental evidence indicates that the amount of fat carried is not maximized for a given set of circumstances, but optimized, at least partly because of a need to trade off starvation risk against predation risk, part of which may be mass-dependent, and therefore increased by carrying increased reserves. Evidence for such a trade-off strategy includes the observed negative correlation between fat reserves and ambient winter temperature operating as a proximate factor. 2. However, the relationship between fat and temperature requires further investigation for two reasons. First, field evidence that temperature acts as a proximate factor is equivocal. Secondly, measures of temperature used (e.g. mean temperature over the previous 24 h) have given little resolution as to the time over which temperature effects operate, and whether low temperatures might constrain the bird's ability to fatten, in addition to signalling the need to fatten further. 3. This paper uses observations of fat from a wild great tit population, studied over 17 years, to address these two areas. First, it demonstrates that temperature acts as a proximate factor influencing fat reserve levels. Secondly, by relating the time of observation more precisely than previously to temperatures prevailing at particular times during the previous 24 h, it is shown that while past temperature (e.g. 5 + h previously) is used to optimize fat reserves (strategic fattening), more immediate temperature may constrain the bird's ability to achieve the optimum. 4. This constraint is demonstrated by a positive correlation between fat reserves and current temperature; probably the first demonstration of such a relationship. However, this constraining effect of temperature has diminished over the last 17 years, presumably because of climate amelioration.
Journal of Animal Ecology, 2007
Cyclic daily fattening routines are very common in wintering small wild birds, and are thought to be the consequence of a trade-off between different environmental and state-dependent factors. According to theory, these trajectories should range from accelerated (i.e. mass increases exponentially towards dusk) when mass-dependent predation costs are the most important cause of mortality risk, to decelerated (i.e. the rate of mass gain is highest at dawn and decreases afterward) when starvation is the greater risk. 2. We examine if geographically separate populations of coal tits, wintering in Scotland and central Spain under contrasting photoperiods, show differences in their strategies of daily mass regulation. We describe population differences in wild birds under natural conditions, and experimentally search for interpopulation variation in diurnal body mass increase under common, manipulated, photoperiod conditions (LD 9 : 15 h vs. 7 : 17 h), controlling for temperature, food availability, predator pressure and foraging arena. 3. Winter diurnal mass gain of wild coal tits was more delayed towards the latter part of the daylight period in central Spain (i.e. the locality with longer winter days) than in Scotland. In both localities, the pattern was linked to the average mass at dawn, with mass increasing more rapidly in lighter birds. However, under the controlled photoperiod situation the pattern of daily mass gain was similar in both populations. Diurnal body mass gain was more accelerated at the end of the day, and the increase in body mass in the first hour of the day was considerably lower under the long (9 h) than under the short (7 h) photoperiod in both populations. 4. Wintering coal tits show patterns of mass gain through the day that are compatible with current theories of the costs and benefits of fat storage, with birds at lower latitudes (with longer winter days) having a greater tendency to delay mass gain until late in the day. The experimental study revealed that these patterns are plastic, with birds responding directly to the photoperiod that they experience, suggesting that they are continually making finescale adjustments to energy reserves on the basis of both inherent (e.g. state-dependent) and extrinsic cues.
Journal of Ethology, 2015
Winter is one of the crucial periods of the bird's year-round life cycle. Fat reserves in bird species are prone to a wide range of factors, with weather conditions and a bird's social status being two major ones. In our study we analysed the variation in fat reserves in birds with stable, constant access to food resources in three of the most common wintering species: the great tit Parus major, the blue tit Cyanistes caeruleus and the greenfinch Chloris chloris. The highest mean value of fat score was found in the greenfinch, whereas in both species of tits these values were equally lower. For all three species the amount of fat reserve was correlated with the same factors. It increased together with the decrease of mean average temperature, and with the course of daytime as well as the season-site index (calculated as data collected at a given site in a particular year). Contrary to many previous surveys we did not find dependence of the fat score level on individual dominance status, which is probably linked to the abundance of food in catching sites.
Understanding the potential limits placed on organisms by their ecophysiology is crucial for predicting their responses to varying environmental conditions. Studies to date have traditionally relied on between-species comparisons, however, recently, there has been a growing recognition of the importance of intraspecific variation in shaping an organism’s ecological and physiological responses. In this context, widely distributed resident bird species offer a well-suited study system to examine intraspecific geographical variation in ecophysiological traits. A main hypothesis for explaining avian thermoregulatory mechanisms is the aerobic capacity model, which posits a positive correlation between basal (BMR) and summit (Msum) metabolism, caused by the energetic maintenance costs associated with increased muscle mass for shivering thermogenesis and enhanced investment in digestive organs for food processing. Most evidence for this hypothesis, however, comes from interspecific compari...
Animal Behaviour, 2006
Theoretical and experimental evidence suggests that an increase in flight costs will decrease flight performance, and that birds should trade-off the benefits of body reserves to minimize these costs. Alternatively, birds could avoid starvation by increasing food intake, thereby maintaining body reserves, and/or decreasing flight activity to compensate for the greater per unit flight costs. To test the effect of increased flight costs on body mass regulation and on flying and feeding activity, we experimentally manipulated wing area in a free-ranging wintering population of coal tits, Periparus ater, and in captive birds living in a less restrictive environment (large outdoor aviaries). In the field, body mass decreased when wing area was reduced, but heavier birds lost more weight than lighter birds as a consequence of an allometric increase in flying costs. However, wing area reduction had no effect on body mass in the aviaries. Birds also flew less when wing area was reduced and those with higher wing loadings decreased flying frequency more markedly. We suggest that the goal of small resident birds living in a Mediterranean montane climate would be to maintain daily fat reserves within narrow limits during autumn and winter, even under contrasting ecological conditions.
Behavioral Ecology, 2002
In a dominance-structured flock, social status may determine priority of access to food. Birds of low social status may perceive present and future access to food as less predictable, and so have a higher risk of starvation, than birds of high social rank. Theoretical models predict that subordinate birds should carry larger fat reserves and incur higher mass-dependent costs than dominants. However, empirical tests of the assumptions of these models are still scarce and controversial. We investigated the effect of dominance rank on daily mass gain under conditions of fluctuating food availability in a laboratory experiment using four flocks of four coal tits (Parus ater) each. The same amount of food was delivered in two treatments, but in one treatment the food was offered at a constant rate between days (fixed treatment), while in the other treatment the daily food supply varied in an unpredictable sequence between days (variable treatment). All birds showed greater variance in body mass in the variable treatment than in the fixed treatment. Body mass within birds showed the same variability at dawn than at dusk in the fixed treatment, but less variability at dawn than at dusk in the variable treatment. This may be a mechanism to reduce the immediate risk of starvation at the beginning of the day, when fat reserves are at their lowest and the aggression between flock members when feeding highest. Subordinate birds were excluded from the feeders by dominants more often in the early morning than in the rest of the day, and they showed more variability in daily mass gain and body mass at dawn than dominant birds. These results support the hypothesis that subordinate birds have a reduced probability of surviving when food availability changes unexpectedly compared to dominants.
We studiedt he interactionsb etweenw eather,s ocial dominancea nd body condition (fat and protein reserves)i n a colour-ringedp opulation of the Great Tit in the Killarney National Park, Rep. of Ireland in two mild winters (1990 and 1992) differingm arkedlyi n rainfall.R ainfall,b ut not temperaturew, as a strong predictor of mean daily fat levels (birds were fatter on wetter days) but did not predict muscle score. The birds were also fatter in the wet winter than the dry one, and this was a greater difference than predicted by daily rainfall alone. The effects of rainfall are considered in the context of ultimate and proximate cues to fattening. In contrast, muscle scores were greater in the dry year than the wet. On average, birds known to have survivedf romt he 1990t o the 1992w interh ad higherm uscles cores,i rrespective of their age or sex, in 1990 than those not seen again. In the wet winter, muscle score (but not fat) was positivelyc orrelatedw ith a measureo f individuald ominancei;n the dry winter fat was negatively related to dominance, and no relation was found between muscle score and dominance. These results indicate that individual differences in condition reflect differences in individual status, and that experienced environmentacl onditions stronglyi nfluencet he relationshipb etween social status and body reserves. This is the first field study of Great Tits relating condition and dominance among individuals rather than among status classes. We suggest that, under some circumstances muscle may be a better indicator of condition than fat.
Journal of Avian Biology, 1999
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Long-term repeatability of winter basal metabolic rate and mass in a wild passerine
Functional Ecology, 2009
Basal metabolic rate (BMR) is an important trait in the study of energy management of an individual, especially in small wintering passerines from the north which have one of the highest energy turnover rates in vertebrates. Laboratory studies have shown the trait to be repeatable and heritable, despite its plastic nature. However there is currently a lack of empirical data from wild passerine populations. 2. We studied within-and between-year repeatability of BMR, body mass and mass-independent BMR from two populations of wintering great tits ( Parus major ) at the northern range of their distribution. 3. We found body mass, BMR and mass-independent BMR to be highly repeatable both within and between years. 4. Our results provide the first evidence from a wild small passerine that, despite a large environmentally induced variation in metabolic rate, individuals show consistent metabolic strategies over periods even longer than a year. 5. Homeotherm species exposed to new or changing environmental conditions may be able to evolve specific energetic strategies in the wild, as previously found in captive species.
Body mass regulation in resident and transient wintering siskins Carduelis spinus
2001
Abstract. Birds regulate body mass according to the trade-off between the benefits (eg energy insurance) and the costs (eg predation risk) of carrying reserves. As a consequence, several factors as ability to find food resources, dominance status, and energetic constraints related to flight, can equally determine the body mass of an individual.