Barn Swallow Hirundo rustica parents work harder when foraging conditions are good

In altricial birds, the great effort involved in supplying food to nestlings can create trade‐offs in the allocation of resources between the current brood and parental self‐maintenance. In poor foraging conditions, parents have to adjust their energy expenditure in relation to the increased foraging costs. However, intra‐specific variation in parental energy expenditure has rarely been evaluated in the context of these trade‐offs. Here, we quantified the daily energy expenditure (DEE) of parent Barn Swallows Hirundo rustica during the nestling period in relation to foraging conditions while controlling for differences in brood size and nestling age. DEE varied substantially with environmental conditions, increasing by 10 kJ/day per 5 °C in ambient temperature, and by 11 kJ/day per hour in day length. Parent birds did not compensate for a poor aerial insect supply on cool days, but reduced their DEE. Parents only slightly buffered a negative energy balance during chick provisioning with stored body reserves. They did not sacrifice their own energy demands to keep up a high energy flow to the brood when foraging conditions were poor. Instead they worked harder when foraging conditions allowed a surplus intake, fully compensating for their additional efforts, and made maximum use of the rich food supply, allowing the brood to accrue body reserves to compensate for low food intake on cold days. This strategy of energy management may have evolved in the context of the adaptation to the aerial foraging mode and to the ephemeral nature of aerial food resources.     

Variable energetic responses to clutch size manipulations in white-throated dippers Cinclus cinclus

We used the doubly-labelled water technique to measure daily energy expenditure (DEE) of a free-living uniparental incubator, the white-throated dipper Cinclus cinclus , in Scotland. DEE was 205±8 (s.e.m.) kJ d⁻¹ for 17 females incubating their natural clutch sizes, equivalent to 3.2±0.1×basal metabolic rate (BMR). To investigate the influence of clutch size on the energy budget, we measured the DEE of 14 females with clutches increased or reduced by a single egg. Birds with reduced clutch sizes had an energy expenditure with a mean and variance that did not differ from those of birds with unmanipulated clutches. Enlarging the clutch led to an increase in energy expenditure to over 4×BMR for some individuals but not for others, resulting in greater variance in energy expenditure for birds with enlarged clutches. Individual variation in energy expenditure could not be fully explained by environmental conditions, by patterns of behaviour or clutch size. Incubating females received a maximum of only 4 kJ d⁻¹ (2% of DEE) from provisioning by the male, and mobilised up to 6 kJ d⁻¹ (3% of DEE) from reserves. Females spent 2.9±0.2 h (n=20) away from the nest each day, so a foraging rate of 95 kJ h⁻¹ was required during incubation recesses to balance DEE. This 'required foraging rate' is double previous estimates of the maximum rates of energy acquisition for birds of this size. We suggest that the greater likelihood of a raised energy expenditure associated with larger clutches, combined with the difficulties in maintaining energy supplies, may constitute a constraint on avian clutch size.     

Annual cycle of energy and time expenditure in a golden-mantled ground squirrel population

Summary We have analyzed seasonal shifts of energy and time allocation in a population of golden-mantled ground squirrels (Spermophilus saturatus) by directly measuring total daily energy expenditure (DEE) with an isotopic technique (doubly labeled water=dlw), and by estimating components of total DEE through an integration of field behavioral observations with laboratory-measured rates of energy expenditure (oxygen consumption) associated with major behavioral and physiological states. Hibernation laster about 7 1/2 months, and the 4 1/2-month activity season consisted of mating, a 28-d gestation of 3–5 young, 5 1/2 weeks of postnatal growth building to a peak in lactation just before the young emerged above ground, an additional 2–3-week period of maternal care before dispersal, and finally restoration of body mass preceding hibernation. Although the hibernation season comprised nearly two-thirds of the year, it involved only 13–17% of annual energy expenditure, leaving about 85% of energy expenditure for the active season. Ground squirrels were actually present on the surface for only about 11% of the year's time, and the foraging time required to obtain the total annual energy supply amounted to only about 2% of the year's time. The squirrels fed mainly on herbs in the early season and hypogeous fungi later; both were used extensively during peak lactation when female energy expenditure and demand were maximal. Average daily foraging time increased steadily throughout the season to a maximum of 28% of aboveground time as availability of greens diminished and fungus predominated in the diet; time availability did not limit foraging since the animals sat on average for 65% of the daily surface time of about 7 h. Timing of reproduction is apparently optimized such that peak reproductive energy demands are matched with maximal food availability and moderate thermal conditions that minimize energy demand. Despite the greater body mass of males, the greatest total DEE (measured by dlw) of any squirrels at any time of year was that of females during peak lactation. For production of young and lactation through above-ground emergence of an average litter of 2.7, females required a total energy increase of 24% above annual nonreproductive metabolism. Yearling females all bred and performed similarly to older females, yet some costs were greater because the yearlings began and ended hibernation at smaller mass, compensated by giving birth later, and finally showed a greater absolute increase in body mass over the active season than older females. Annual metabolic energy expenditure of breeding males was about 18% greater than that of females, due to greater male body mass. Yet the annual energy intake requirement for both sexes was essentially identical (about 42MJ) due to the greater reproductive export by females in the form of newborn and milk. During the mating season males showed wide-ranging exploratory behavior and social interactions, including aggression, that involved considerable locomotory energy expenditures. Although we did not directly account for the energetics of these specific reproductive behaviors, they are critical to male reproductive success and on a daily basis they probably involved much greater energy expenditure than sperm production. Some yearling males avoided these costs by foregoing testicular development, yet they allocated four times as much energy to growth as older males, thereby increasing somatic condition for the future.     

Seasonal Variation in Parental Care Drives Sex-Specific Foraging by a Monomorphic Seabird

Evidence of sex-specific foraging in monomorphic seabirds is increasing though the underlying mechanisms remain poorly understood. We investigate differential parental care as a mechanism for sex-specific foraging in monomorphic Common Murres (Uria aalge), where the male parent alone provisions the chick after colony departure. Using a combination of geolocation-immersion loggers and stable isotopes, we assess two hypotheses: the reproductive role specialization hypothesis and the energetic constraint hypothesis. We compare the foraging behavior of females (n = 15) and males (n = 9) during bi-parental at the colony, post-fledging male-only parental care and winter when parental care is absent. As predicted by the reproductive role specialization hypothesis, we found evidence of sex-specific foraging during post-fledging only, the stage with the greatest divergence in parental care roles. Single-parenting males spent almost twice as much time diving per day and foraged at lower quality prey patches relative to independent females. This implies a potential energetic constraint for males during the estimated 62.8 ± 8.9 days of offspring dependence at sea. Contrary to the predictions of the energetic constraint hypothesis, we found no evidence of sex-specific foraging during biparental care, suggesting that male parents did not forage for their own benefit before colony departure in anticipation of post-fledging energy constraints. We hypothesize that unpredictable prey conditions at Newfoundland colonies in recent years may limit male parental ability to allocate additional time and energy to self-feeding during biparental care, without compromising chick survival. Our findings support differential parental care as a mechanism for sex-specific foraging in monomorphic murres, and highlight the need to consider ecological context in the interpretation of sex-specific foraging behavior.     

Incubation and brooding rhythm of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Incubation and brooding performance of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica, in the 1991 -1992 austral summer is reported in detail and compared with data from two other areas. There was an inverse relationship between the mean foraging trip length and mean peak weight of chicks. Variation in shift length throughout incubation resulted from a combination of seasonal effects (food supply) and behavioural adjustment to hatching. The length of the last incubation shift was independent of its number but decreased with date of initiation. The average weight of nestattending birds increased steadily during the incubation period and at the same rate in both sexes. Females attained seasonal peak body-weight before the egg hatched, whereas males just recovered their pre-breeding weight. Males took on a slightly larger share of incubation (52%, range 40–63%) and invested more time in mutual nest attendance. Length of foraging trips varied consistently in pairs and individuals, its repeatability being twice as high in females as in males. The incubation performance of individual females (length of the first and an average foraging trip) was correlated with the size of the egg they had laid and also to subsequent chick growth and fledging success. There was a tendency in successful pairs to spend more time together at the nest and to have shorter foraging trips. I suggest that variation in breeding performance among pairs was mainly a result of individual variation in female quality, with pairs where the female contributed more to incubation being more successful. There is little evidence that egg losses were caused by parental errors.     

Energy allocation for reproduction in a marsupial arboreal folivore,the common ringtail possum (Pseudocheirus peregrinus)

This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day^–1 or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg^–1 year^–1. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg^–1 year^–1, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day^–1) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed.     

Predation by sparrowhawks Accipiter nisus on male and female pied flycatchers Ficedula hypoleuca in relation to their breeding behaviour and foraging

Bright plumage, song display, and aggressive resource defence in males may cause higher predation on males than on females during the breeding season. However, in birds, higher predation on females is sometimes observed. Parental investment may be high in females (egg-laying, incubation and feeding of offspring), which might lead to a high risk of predation. We studied predation by sparrowhawks Accipiter nisus in relation to behaviour in pied flycatchers Ficedula hypoleuca where breeding males are more conspicuous than females in plumage and behaviour. Male pied flycatchers generally occupied more exposed perches than females. Females were more mobile and foraged more than males, especially prior to and during incubation. During the incubation and nestling stages, when predation on the sexes could be directly compared, sparrowhawks took about the same number of male and female pied flycatchers. During incubation, however, females spent about 77% of the day in the nest and were 4.7 times more vulnerable than males per unit of time available (i.e. outside the nest). A comparison with the chaffinch Fringilla coelebs , where hawks took more females than males, indicates that timing of breeding, foraging behaviour and parental roles of males and females affect predation risk.     

Feeding or Resting? The Strategy of Rutting Male Alpine Chamois

Optimal foraging theory suggests that animals normally maximize energy intake to optimize their energy balance. However, when efficiency to assimilate energy falls below the level necessary to ascertain basal energetic requirements, they should shift to an energy saving strategy. Males of many ruminant species considerably reduce their food intake during the rut. Nevertheless, they are commonly assumed to maximize energy intake besides their investments in rutting activities. Based on predictions of optimal foraging theory and the specific ruminant digestive physiology, we propose, however, that rutting males in polygynous species with time consuming mating tactics should instead use an energy saving strategy. Particularly, we predict this to be the case in Alpine chamois (Rupicapra rupicapra rupicapra), a highly polygynous mountain ungulate, of which the males defend mating territories during the rut. By combining observational and telemetry data of eight radio‐collared males we constructed individual 24‐h time budgets, and compared the behavior of males before, during and after the rut. Males spent significantly less time feeding during the rut (0.9 h) compared with before (8.5 h) and afterwards (6.4 and 7.5 h, respectively), whereas time spent lying remained more or less unchanged (pre‐rut; 12.7 h, rut; 13.3 h, post‐rut; 12.9 and 13.9 h, respectively). The ratio of time spent feeding to lying dropped from 0.67 in the pre‐rut period to 0.05 in the rutting period. As a result, males allocated on average approx. 90% of their non‐rutting time to lying, and a negative relationship between rutting and lying time emerged. Hence, males seemed to trade lying time against rutting time. We conclude from these results that male Alpine chamois do not maximize their energy intake during the rut, but rather adopt an energy saving strategy to optimize their energy balance.     

Reversed sexual size dimorphism and parental care in the Red-footed Booby Sula sula

The 'division-of-labour' hypothesis predicts that males and females perform different roles in parental care and that natural selection acts differently on each sex so as to produce different body size optima suited to their particular roles. Reversed sexual size dimorphism in avian species (females larger than males) may therefore be an adaptive consequence of different roles of males and females in parental care. We investigated patterns of nest attendance, brooding, foraging and provisioning rate in a tropical seabird, the Red-footed Booby Sula sula , a species showing a reversed sexual size dimorphism. During incubation, females attended the nest more often than males, and spent more time brooding the small chick than did males during daytime. Males and females did not differ in the average duration of their foraging trips. During incubation, there was a positive relationship between nest attendance and the duration of foraging trips in males, but not in females. During the small-chick stage, for the same time spent at the nest, males spent significantly more time than females at sea. On average, females fed the chick more often than did males. In males, there was a significant and positive relationship between the probability of feeding the chick and the duration of the foraging trip, whereas in females, this probability was much less dependent on the duration of the foraging trip. Overall, female Red-footed Boobies achieved slightly, but significantly, more parental commitment than did males. However, these sexual differences in parental participation were small, suggesting a minimal division of labour in the Red-footed Booby. Our results suggest that the division of labour hypothesis is unlikely to explain fully the adult size dimorphism in Red-footed Boobies.     

Division of labour during incubation in a woodpecker Colaptes auratus with reversed sex roles and facultative polyandry

The contribution of males to incubation has rarely been studied in altricial birds because the pursuit of extra mating opportunities is believed to conflict with incubation. Woodpeckers show reversed sex roles in parental care with males doing most of the nest construction, incubating and brooding of the young while females may be polyandrous. I investigated incubation by each sex at 71 monogamous and four polyandrous nests of the Northern Flicker Colaptes auratus , predicting that males would contribute to incubation according to their energy reserves (body condition) whereas females would contribute based on alternate reproductive opportunities. Nest attendance was 99% with males contributing a mean of 66% of the total incubation including nocturnal incubation. The length of daytime bouts averaged about 2 h and did not differ between the sexes. Consistent with predictions of investment strategies, structurally larger males and those in poorer body condition incubated less than smaller males, perhaps because they required more recess time to forage or to conserve energy. Older females contributed less incubation than young females and polyandrous females contributed less incubation at their secondary nests than monogamous females. Incubation period, nest depredation rate and hatching success were not influenced by bout length, number of bouts or relative contribution of the sexes. Hatching success was 86% at nests of both monogamous and polyandrous females because males compensated for reduced female participation. Because incubation of the sexes is compensatory and not additive, incubation pattern did not influence short-term reproductive success. I conclude that males invest in incubation according to their energy needs, and females may adjust their contributions based on alternate reproductive tactics.     

The energetics of reproduction and parental care in the terrestrial isopod Porcellio laevis

Parental care is a behavioral strategy that contributes to increased fitness of progeny. Among terrestrial arthropods, many isopods provide extensive parental care. Few studies have quantified the underlying cost of parental care in terms of energy. We used the terrestrial woodlouse Porcellio laevis (Latreille) as a study model to examine how energetic acquisition and expenditure in females is affected during the incubation period and how parental care affects energy balance in this species. We determined the basic reproductive biology (i.e. fecundity, reproductive output, egg volume, egg loss), energy expenditure (i.e. metabolic rate), and energy acquisition (i.e. food consumption, digestibility) of ovigerous females in different stages of embryonic development. Non-ovigerous females were used as the control group. Our results show that P. laevis displays variability in life-history traits compared with populations from other zones around the world. Ovigerous females exhibited a lower ingestion rate and lower digestibility than control females, thus indicating a lower capacity for energy acquisition. Furthermore, energy expenditure was higher in ovigerous females when compared to non-ovigerous females. In particular, females in early embryonic development stored 5.1-fold less daily energy than females without eggs.

The results presented here show that the parental care provided by female P. laevis is energetically costly. Overall, our work brings us much closer to understanding the proximate mechanisms of the costs of parental care in terrestrial isopods. Both proximal mechanisms and consequences of providing care on future reproduction, should be considered in explaining the evolution of parental care.     

Energetic limitation of avian parental effort: Field experiments in the kestrel (Falco tinnunculus)

We studied the limiting factors for brood size in the kestrel, Falco tinnunculus, by measuring parental effort in natural broods of different size and parental response to manipulation of food satiation of the brood. Parental effort was quantified as total daily time spent in flight, and total daily energy expenditure, from all-day observations. During nestling care males with different natural brood sizes (4 to 7 chicks), spent an average of 4.75 h · d^?1 in flight independent of brood size, and expended an average total daily energy of 382 kJ · d^?1. Due to a higher flight-hunting yield (mammal-prey caught per hour hunting), males with larger natural broods were able to provision their broods with the same amount of food (mainly Microtus arvalis) per chick (62.6 g · d^?1), with the same effort as males with smaller broods. This provisioning rate was close to the mean feeding rate of hand-raised chicks in the laboratory, that were fed ad libitum, (66.8 g · d^?1 · chick^?1). Our food deprivation experiments revealed that male kestrels strongly respond to food shortage in the nest. In the older nestling phase males on average increased their daily rate of food delivery to the nest as a response to experimental food deprivation by almost three times to 646.4 g · d^?1, by increasing their flight activity level from 4.46 to 8.41 h · d^?1. This increased energy expenditure was sustained, for as long as eleven days, by increasing the metabolizable energy intake up to what is presumed to be the maximum rate. Even under considerable experimental food stress (chicks not being satiated due to continuous removal of delivered food by the observers) about half of the available daylight time remained unused for foraging. We conclude 1) that the mean daily energy expenditure of males during nestling care — to which clutch size is apparently initially adjusted — is well below the maximum they are able to sustain and 2) that the energy expenditure they can sustain under extremely high nestling demand is not set by the available time for foraging or the available energy in the environment. Thus the birds normally operate well below their presumed maximum, and only during food shortage, e.g., as caused by our experiments, do they increase activity up to this maximum. Therefore we conclude that the kestrels have costs other than energy expenditure, such as parental survival, that are involved in the increased “cost” of parental effort. We discuss possible generalisations about existing energetic limitations during parental care in altricial birds. From published estimates of daily energy expenditure during parental care (DEE_par) in 30 different bird species we derived the equation: DEE_par = 14.26 kg^0.65 Watt. This relationship differs significantly in slope (T = 2.49; p > 0.02) from the allometric equation for the maximum rate of energy assimilation (DME_max) as provided by Kirkwood (1983): DME_max = 19.82 kg^0.72 Watt. In smaller species (ca. 25 g) DEE_par about equals DME_max, while in the larger species (ca. 10 kg) DEE_par represents only about 60% of the predicted DME_max. This suggests that limitations in parental effort are more frequently set by the maximum sustainable energy intake in the smaller species than in larger species. Our allometric equations for DEE_par suggests that the relation between BMR, estimated using the equations of Aschoff and Pohl (1970), and the observed parental energy expenditure, is such that on average bird parents work at a daily level somewhere between 3 and 4 times BMR.     

Incubation energetics of the Laysan Albatross

Summary The energy expenditure of incubating and foraging Laysan Albatross (Diomedea immutabilis, mean body weight 3.07 kg) was estimated by means of the doubly-labelled water technique. During incubation, the energy expenditure was similar to that of resting birds that were not incubating an egg. The energy expenditure of foraging albatross (2072 kJ/day) was 2.6 times that of resting birds. It was concluded that the energy expenditure of the tropical Laysan Albatross was not less than that of species foraging over cold, high-latitude oceans. An energy budget compiled for an incubating pair of albatross revealed that the energy expenditure of the female was greater than that of the male bird, during the incubation period.     

Body condition and retaliation in the parental effort decisions of incubating great frigatebirds (Fregata minor)

Decisions about parental effort have the potential to be affectedby an individual's body condition and, among species with biparentalcare, by the level of effort made by one's mate. Previous studies,primarily of short-lived species, have found that a reductionin the parental effort of one pair member typically leads toa compensatory increase by the mate. However, long-lived specieswith short-term pair bonds might be expected to retaliate, ratherthan compensate, for a reduction in a mate's effort. I studiedthe factors affecting parental effort decisions during incubationby the great frigatebird, a long-lived seabird that forms newpair bonds for each breeding attempt. During incubation, malesand females took turns incubating and foraging. Individualslost mass during an incubation shift and regained this massduring the subsequent foraging bout. If an individual was lefton the nest for a long period of time while its mate was foraging,it subsequently went on a long foraging trip after being relievedby its mate, despite the fact that longer shifts were likelyto lead to nest failure. This relationship between incubationshift length and duration of subsequent foraging excursion could be due to a need to regain body condition after a longfast, or it could reflect a retaliatory response to the mate'sprolonged absence. To test these alternatives, I conducteda food supplementation experiment. Individuals engaged in along incubation shift were assigned to a control group or toa treatment group that was fed until the end of that particularincubation shift. Overall, fed birds returned from the subsequentforaging trip sooner than control birds, demonstrating thatthe relationship between incubation shift duration and foragingtrip duration is due primarily to a need to increase body mass,rather than being a retaliatory response to a mate's low levelof parental effort. However, males and females differed in theextent of their responses to the experimental treatment, indicatingthat males may also exhibit some degree of retaliation.     

Energetic demands during brood rearing in the Wheatear Oenanthe oenanthe

Daily energy expenditure of Wheatears Oenanthe oenanthe during the brood rearing period was measured using the doubly-labelled water technique. The average daily metabolic rate (ADMR) (± 1 s.d.) for 24 individuals was 6.24 ± 1.17 cm³ CO₂/g/h, which corresponds to 95.3 ± 17.0 kJ/day (RQ = 0.75) for a bird of average mass (24.3 g).
There were no significant differences in daily energy expenditure between the sexes, nor between first-year and older birds. Individual males with longer tarsi had lower ADMR but raised larger broods. The ADMR increased at lower ambient temperatures, but this effect disappeared when the positive correlation with rainfall was taken into account. There was no relationship between the natural brood-size and parental daily energy expenditure. A positive correlation between ADMR and the time spent hopping and pecking suggests that foraging activity may account for some of the variability between individuals. The daily change in body-mass was not related to either the individual's age or its sex, and overall was not correlated with the level of daily energy expenditure. For birds examined on the same day, individuals with a higher ADMR had a greater loss of body-mass, which appears to be a high risk strategy. However, Wheatears also exhibited an ability to increase body-mass in conjunction with a drop in their daily energy expenditure.     

Estimation of food intake and ingested energy in Daubenton’s bats (Myotis daubentonii) during pregnancy and spermatogenesis

We studied food intake of and estimated ingested energy in female and male Myotis daubentonii during the periods of pregnancy (period 1, 8 May–4 June) and of intense spermatogenetic activity (period 2, 24 July–22 August) over 8 years (1996–2003) in central Germany. We used radiotelemetry to determine the time spent foraging and marked animals with chemiluminescent light-sticks to determine prey attack rates. Body length, body mass, moisture content, and caloric content of chironomids, the main prey of Daubenton’s bats, were measured to estimate the nightly food intake and, in consequence, energy intake. Pregnant females spent significantly more time foraging than males during period 1 and females during the post-lactation period. In contrast, male foraged longer during the period of highest spermatogenetic activity than during late spring and also significantly longer than post-lactating females. Based on a mean number of 8.3 prey attacks per minute, the time spent foraging, and a capture success rate of either 50 or 92%, calculated intake values with a feeding rate of 7.6 insects per minute (=92% capture success) were more consistent with literature data for other insectivorous bats than that of values calculated on the basis of a capture success rate of 50%. In the high capture-success model, calculated insect intake of female bats was 8.0 g during pregnancy and 4.9 g per day during post-lactation, providing 5.0 and 3.0 kJ of ingested energy per gram body mass per day. Calculated intake of male bats was 3.6 g insects per day during late spring and 8.0 g during period of intensive spermatogenesis, providing 2.6 and 5.7 kJ of ingested energy per gram body mass.     

Energy balance and brown adipose tissue thermogenesis during chronic endotoxemia in rats

The effects of continuously administered endotoxin on 7-day energy balance were investigated in male rats. Three groups of rats were implanted with osmotic pumps; two groups received saline-filled pumps, whereas the third received endotoxin. One of the saline groups was pair fed to match the food intake of the endotoxemic rats. After 7 days, body energy and protein and fat contents of rats were determined together with the energy content of food and feces. Endotoxin infusion not only induced fever, but it also suppressed appetite and significantly decreased body weight gain. Metabolizable energy intake was reduced by approximately 20% in infected rats. Although protein and fat gains were lowest in the endotoxin group, there appeared to be a selective loss of protein when considered as percent of body weight. Percent body fat was unaltered between the groups. Energy expenditure considered in absolute (kJ) or body weight-independent (kJ/kg0.67) terms yielded similar patterns of results; expenditure (kJ) was 10 and 20% (P less than 0.05, P less than 0.01) lower in the endotoxemic and pair-fed rats, respectively, compared with controls. Hence, compared with pair-fed rats, endotoxin-infused animals had a 10% rise in their expenditure. Brown adipose tissue thermogenesis was assessed by mitochondrial binding of guanosine 5'-diphosphate, and results showed that binding was greatest in endotoxemic rats and lowest in the pair-fed animals. The present results suggest that in this endotoxemic model appetite suppression exacerbates changes in energy balance. However, the reduction in body weight gain is also dependent on a decrease in metabolic efficiency and an increase in total energy expenditure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Energy expenditure and water flux of Rüppell's foxes in Saudi Arabia

Scattered populations of Rüppell's foxes (Vulpes rueppelli) occur across the deserts of northern Africa and Arabia. Little is known about the biology of these canids, especially the physiological mechanisms that contribute to their ability to live in such harsh environments. For individuals from Saudi Arabia, we tested the hypotheses that Rüppell's foxes have a reduced basal metabolic rate and total evaporative water loss (TEWL), parameters measured in the laboratory, and a reduced field metabolic rate (FMR) and water flux when free-living. Under basal conditions in the laboratory, males, which averaged 1,858 g in body mass, had an oxygen consumption of 914.9 mL O(2)/h, whereas females, which weighed on average 1,233 g, consumed 682.9 mL O(2)/h; rates of oxygen consumption translated to 441.4 kJ/d and 329.4 kJ/d, respectively. TEWL averaged 52.6 g H(2)O/d for males and 47.5 g H(2)O/d for females. We found no evidence that basal metabolism is reduced in Rüppell's foxes, but their TEWL was remarkably low: 50.9% of allometric prediction for males and 64.5% for females. In the wild during winter, males expended energy at a rate of 1,306.5 kJ/d, whereas females had an expenditure of 722.8 kJ/d. Analysis of covariance with FMR as the dependent variable, sex as a fixed factor, and body mass as a covariate showed no statistical difference in FMR between sexes. Water flux did not differ significantly between sexes and averaged 123 mL H(2)O/d, a value 30% lower than the kit fox from the deserts of southwestern North America. FMR was positively related to nocturnal activity levels as FMR (kJ/d) = -2,900.1+55.5 (% of time moving). The water content of prey items varied between 1.9 and 4.1 g H(2)O/g dry matter consumed. Based on these values and knowledge of their diet, we calculated that foxes captured about one rodent and a variety of anthropods per night of foraging.     

Sex-specific foraging behaviour in a seabird with reversed sexual dimorphism: the red-footed booby

Most hypotheses attempting to explain the evolution of reversed sexual dimorphism (RSD) assume that size-related differences in foraging ability are of prime importance, but the studies on sex-specific differences in foraging behaviour remain scarce. We compare the foraging behaviour of males and females in a seabird species with a RSD by using several miniaturised activity and telemetry loggers. In red-footed boobies males are 5% smaller and 15% lighter than females, but have a longer tail than females. Both sexes spend similar time on the nest while incubating or brooding. When foraging at sea, males and females spend similar time foraging in oceanic waters, forage in similar areas, spend similar proportion of their foraging trip in flight, and feed on similar prey—flying fishes and flying squids—of similar size. However, compared to males, females range farther during incubation (85 km vs. 50 km), and furthermore feed mostly at the extremity of their foraging trip, whereas males actively forage throughout the trip. Males are much more active than females, landing and diving more often. During the study period, males lost mass, whereas females showed no significant changes. These results indicate that males and females of the red-footed boobies differ in several aspects in their foraging behaviour. Although some differences found in the study may be the direct result of the larger size of females, that is, the slightly higher speeds and deeper depths attained by females, others indicate clearly different foraging strategies between the sexes. The smaller size and longer tail of males confer them a higher agility, and could allow them to occupy a foraging niche different from that of females. The higher foraging effort of males related to its different foraging strategy is probably at the origin of the rapid mass loss of males during the breeding period. These results suggest that foraging differences are probably the reason for the differential breeding investment observed in boobies, and are likely to be involved in the evolution and maintenance of RSD.     

Parental behaviour in the Lapwing Vanellus vanellus

Parental behaviour of monogamous and polygynous Lapwings was studied during incubation and brood care. Both parents attended the nest in 86% of monogamous pairs ( n = 29 pairs). In 14% of pairs, only the male parent continued incubation until the eggs hatched, whereas the female deserted the clutch before or at the end of incubation. There was a clear division of parental roles during incubation. Females spent more time incubating (64% of time) than their mates (27%), whereas males spent more time defending the nest (3%) than females (>1%). Time spent incubating did not differ between monogamous and polygynous males. However, polygynous females spent more time incubating (primary females: 95%; secondary females: 97%) than monogamous females. Biparental care was the most common pattern of post-hatching care, although in some broods either the male or the female parent deserted before the chicks fledged. Division of sex roles was less pronounced in brood care than during incubation. Females spent more time brooding (21%) than males (3%), and females attended their chicks more closely than males. Nevertheless, males and females spent similar amounts of time defending the brood from predators and conspecifics. We suggest that the apparent division of parental roles may be explained by sexual selection, i.e. the remating opportunities for male Lapwings might be reduced if they increase their share in incubation. However, the different efficiency of care provision, for example in ability to defend offspring, may also influence the roles of the sexes in parental care.