Repeatability of basal metabolism in breeding female kittiwakes Rissa tridactyla

We studied kittiwakes (Rissa tridactyla) breeding near Ny-Ålesund (79° N, 12° E) on Svalbard. In 1997, the basal metabolic rates (BMRs) of 17 breeding females were measured during the incubation and chick-rearing periods. The mean body mass of the kittiwakes decreased significantly (by 10%) between the incubation and chick-rearing periods. At the same time, both the whole-body and mass-specific BMRs decreased significantly. There was a positive and significant relationship between the BMR residuals from the incubation period and those from the chick-rearing period. Thus, the BMR of incubating female kittiwakes is a significant predictor of their BMR during the chick-rearing period. New BMR data were collected in 1998 from ten of these females, measured around the chick-hatching date. Repeatability values were calculated using either (i) the data for eight individuals for which three BMR measurements existed, or (ii) all the data from both years, yielding significant repeatabilities of 0.52 and 0.35, respectively. These values indicate that between 48 and 65% of the observed variation in BMR is due to intraindividual variability, while between-individual variability accounts for 35 to 52% of the variation in the BMR. This is the first report of a significant repeatability of the BMR of an endothermic organism across an elapsed time of more than one day.     

Factor affecting body mass of young fat dormics (Glis glis) at weaning and by hibernation

This paper describes the factors affecting body mass at weaning and by hibernation of young fat dormice (Glis glis) We studied a free-living population in 1991 and 1992 in a mixed forest where 100 nest-boxes were placed. In the two years, 128 females used the nest-boxes to give birth and rear their litters and more than 900 dormice have been individually marked. Body mass of young at weaning was positively correlated to body mass of the mother in both years and to birth date in 1991, while litter size was negatively correlated to body mass of the young in 1992 only, when birth took place about two weeks later than in 1991. On the contrary, by the time of hibernation, young born later weighed significantly less than those born earlier in the season, and heavier young at weaning remained heavier by hibernation, while maternal body mass and litter size did not significantly affect body mass of young at this stage. Body mass of the mother was negatively related to the date of parturition and early breeding females lost weight during lactation, while females that bred later did not. It seems, therefore, that early breeding carries a cost that only females in good condition can afford. It appears that females may follow two strategies: those in poor body condition will delay pregnancy so that lactation occurs when environmental feeding conditions are at their best; those in good condition will breed earlier, since they can afford to lose weight during lactation. Their young will have more time to grow before hibernation and the mothers themselves will have a longer period of time for restoring their fat reserves.     

Mass loss in incubating Eurasian dotterel: adaptation or constraint?

Body mass loss is frequently observed in breeding birds: whether this is an adaptive response to a change in the relative value of body stores and locomotion performance or a consequence of energetic constraint is still in debate. The male alone cares for most nests of the Eurasian dotterel Charadrius morinellus , although females assist at a proportion of nests. Energetic costs are probably high in the dotterel's arctic-alpine environment and uniparental care restricts the foraging time available to meet these costs, so that incubating dotterel may have to fuel themselves partly using body stores. Nesting male dotterel lost 7.8% of their mass through the incubation period but were 6.8% heavier during periods of high food abundance. Males that were assisted in incubation by a female were 6.7% heavier than uniparental males. We conclude that, since dotterel were heavier when energetic constraints were lifted, mass loss through incubation was principally a consequence of energetic constraint, rather than adaptive mass optimisation.     

Impaired flight ability during incubation in the pied flycatcher

During the breeding season, many female passerine birds increase in body mass before egg laying, maintain a relatively high body mass during incubation, and then drop back to the original level during the chick-rearing period. The post-hatching reduction in body mass, which can be as large as 10–20%, has been suggested to represent an adaptive mass loss to reduce wing loading, thereby increasing parental flight efficiency when chicks have hatched and have to be fed. Here we present the first study of changes in flight ability from incubation to chick rearing in birds. Wild female pied flycatchers Ficedula hypoleuca flew more slowly during incubation than during chick rearing; a 7% reduction in body mass after the chicks had hatched was associated with a 10% increase in vertical take-off speed. Furthermore, the flight muscle size of the females tracked the reduction in wing load, suggesting that muscle size was adaptively reduced when no longer needed. Since incubation-feeding by males reduces the time females have to spend outside the nest foraging, our results suggest that in addition to increasing female nutritional status and reducing incubation time, incubation-feeding will also reduce predation risk during the period when females face impaired flight ability.     

Change in body mass in relation to breeding phase in bull-headed shrikes

Changes in body mass of both sexes of the bull-headed shrike, Lanius bucephalus, were investigated over the six breeding phases of this species. Standardized body mass (SBM), which was defined as body mass divided by the length of the tarsus, of the males was relatively constant over the phrases, while the SBM of the females changed drastically. In the females, the SBM during egg-laying was higher than the SBM in all the other breeding phases. The SBM of the females did not differ between the incubation and early-nestling phases, and was lowest during the fledgling phase. Mass loss in bull-headed shrikes did not correspond to an adaptive adjustment of body mass to permit a reduction in the power required for flight in the nestling period. It is likely that incubating females constantly maintain their body mass to invest in parental efforts from the incubating to nestling periods.     

Influence of Ecological and Social Factors on Body Mass of Wild Chimpanzees

The chimpanzees (Pan troglodytes schweinfurthii) of Gombe National Park, Tanzania, were weighed regularly over a period of 33 yr, resulting in 1286 measurements on 31 males and 26 females aged 2–43 yr. Female growth slowed at 10 yr and that of males at 13 yr. Median adult body mass is 39 kg for males and 31.3 kg for females. Body mass varied between years. Chimpanzees were heaviest during a period of frequent banana provisioning. They were also heavier when community range size was large and population density within the range was low. Chimpanzees were heavier in the wet than in the dry season and body mass tracked rainfall in the preceding mo except for May in which mass was anomalously low. Dominance rank is significantly correlated with body mass for females but not males. High-ranking individuals tended to maintain more stable mass. Variability in body mass was greater for young and old individuals than for prime adults.     

Body mass dynamics during incubation and duration of parental care in Pacific Dunlins Calidris alpina pacifica: a test of the differential parental capacity hypothesis

Breeding is energetically expensive and individuals face a trade‐off between current and future breeding investment. Due to their production of large eggs, female birds are thought to have substantially higher initial energetic investments than males, which decrease the female's offspring rearing capacity. The differential parental capacity hypothesis argues that this large initial investment limits the ability of female shorebirds to provide extended parental care, which can ultimately lead to offspring desertion. This hypothesis predicts that (1) during early incubation females will be in poorer condition than males, (2) both sexes will lose condition during incubation, but the decline in females will be slower than the decline in males and (3) there will be a positive relationship between female condition and the duration of maternal brood care. These predictions were tested using data on body mass adjusted for body size (as a proxy for condition) and parental care from Pacific Dunlins Calidris alpina pacifica nesting on the Yukon Kuskokwim Delta, Alaska. None of the predictions received support: females were heavier than males in early incubation, the overall pattern during incubation was that males gained mass while female mass remained relatively constant, and there was no relationship between female mass and maternal brood care duration. These results suggest that the factors influencing parental care decisions are more complex than a parent simply caring until it is physiologically unable to do so.     

Costs of incubation and immunocompetence in the collared flycatcher

This paper investigates the costs of incubation in terms of reduced reproductive success and investigates whether incubation competes with immune function for resources. I performed a clutch size manipulation experiment in which two eggs were either removed from or added to the nests of collared flycatchers, Ficedula albicollis, for 1 week during incubation and subsequently returned to their original nests before hatching. To induce immune response, the females were challenged with sheep red blood cells. While the duration of incubation, hatching success and fledgling number did not differ between experimental groups, fledgling condition was significantly lower in broods that had been enlarged during incubation. Neither the females' condition nor their ability to respond to a novel antigen differed between treatments. The relationship between antibody production and female condition was significantly positive, but only among females incubating reduced clutches. I conclude that the costs of incubation in the collared flycatcher are not negligible and are manifested only at the chick-rearing phase.     

Fit is fat: winter body mass of Atlantic Puffins Fratercula arctica

Capsule: Atlantic Puffins Fratercula arctica from Scottish and Norwegian populations were significantly heavier in winter than when rearing chicks.

Aims: To compare body masses of Atlantic Puffins on their wintering grounds off the Faroe Islands with those of birds rearing chicks at colonies in Scotland and Norway.

Methods: We took standardized measurements of wing length and body mass of Atlantic Puffins during the summer chick-rearing period and on the wintering grounds near the Faroe Islands. These measurements were used to estimate seasonal changes in body mass for the two breeding populations. In three cases data were available for individuals weighed both at the colony and on the wintering grounds.

Results: On average, Atlantic Puffins breeding in Scotland and Norway increased their body mass by 20–30% between the chick-rearing period and winter. The very limited individual level data accorded well with the population level estimates.

Conclusions: Our results provide the first estimates of the order of magnitude in mass change between two key life history stages in this species. They indicate that gains in body mass between chick-rearing and winter are at least double the decline in mass previously recorded between incubation and chick-rearing. Given the Atlantic Puffin’s deteriorating conservation status, improved information on seasonal changes in body condition should help determine the underlying causes of die-offs in major wreck incidents such as those reported in recent years.     

Metabolic adjustments in breeding female kittiwakes (<Emphasis Type="Italic">Rissa tridactyla</Emphasis>) include changes in kidney metabolic intensity

Black-legged kittiwakes (BLKIs) reduce self-maintenance cost through reductions in mass-specific basal metabolic rate (BMR), body mass and the size of visceral organs during the chick-rearing period. In the present study, we measured kidney in vitro oxygen consumption and plasma 3,3',5-triiodo-L: -thyronine (T3) levels of incubating and chick-rearing female BLKIs, to test whether the decrease in BMR is caused mainly by decreased metabolic intensity or simply by reductions in the size of organs with high metabolic intensity. Body mass and body condition were lower in chick-rearing birds compared with the incubating birds. In contrast to the previous findings, however, the kidney mass did not differ between the two breeding stages. Plasma T3 levels decreased substantially during the breeding season, indicating a reduction in BMR. Over the same period, kidney mass-specific oxygen consumption decreased (by 17.2%) from the incubating to the chick-rearing stage. Thus, the reduction in BMR found in breeding BLKIs seems partly explained by adjustments in metabolic intensity of visceral organs. Lowered metabolic intensity of visceral organs would permit increased allocation of energy to offspring at the expense of their own self-maintenance.     

Body mass changes in a biparental incubator: the Redshank Tringa totanus

Incubation is a period of high energetic costs and accordingly body mass losses are often detected. Why birds lose body mass during incubation is not well understood; suggestions are that it is either a consequence of energetic constraints or adaptations to an optimal mass trajectory. We studied body mass changes through the incubation period in the Common Redshank Tringa totanus, a biparental incubator, on southern Gotland in the Baltic Sea. In contrast to what has been found in other biparental incubators, body mass of both sexes decreased linearly through the incubation period. The estimated mean body mass loss was 6.7 g (SE 1.7), corresponding to ca. 5% of initial body mass at incubation start. Hatching success in males was not related to body mass and size. In contrast, reproductive success, measured as successful production of fledged juveniles, in males was negatively related to body mass during incubation and positively related to body size. This finding supports the theory that body mass loss might follow an optimal mass trajectory, possibly to increase agility through the chick-rearing stage. However, energy constraints causing body mass loss cannot be ruled out; in fact, it is not unlikely that body mass may change due to a combination of both adaptation and stress.     

Sex-specific patterns in baseline corticosterone and body condition changes in breeding Red-footed Boobies Sula sula

Plasma levels of corticosterone often mirror changes in body condition and parental effort. In seabirds, the brooding of young chicks is often paralleled by a marked decline in adult body condition. This may reflect the trade-off between the needs of the chick to be fed regularly and brooded, and that of the adult to spend enough time at sea to restore its body reserves and find food for the chick. In this paper, we describe changes in body condition and baseline corticosterone levels in a tropical seabird, the Red-footed Booby Sula sula , in which the chick is continuously brooded for 5–6 weeks. Body condition did not decline during the brooding period. Female body condition remained stable throughout breeding whereas male body condition declined significantly during the late chick-rearing period. Baseline corticosterone levels were low during the prelaying phase, increased significantly during incubation and were highest during the brooding period. Later in the chick-rearing period, baseline corticosterone levels decreased markedly in females, but stayed elevated in males. There was no correlation between baseline corticosterone and body condition. Because of the chick's slow growth and reduced daily need for food, brooding in Red-footed Boobies may not require a marked increase in parental effort, and the rise in corticosterone levels is probably more a reflection of slight changes in foraging activity. Red-footed Booby males are 15% smaller than females and we suggest that the decline in male body condition during the late chick-rearing period is likely to result from higher energetic flight costs or a lower foraging efficiency imposed by a smaller body size.     

Body mass regulation during incubation in female common eiders Somateria mollissima

We investigated changes in incubation behaviour induced by body fuel depletion in incubating female common eiders, which, in contrast to pelagic seabirds, fast despite being close to marine food sources. In the Svalbard Archipelago, electronic scales were placed under eider nests and the incubation of six birds was prolonged by using wax-filled eggs. Based on changes in the rate of body mass loss in normally incubating females and in ten captive birds that did not incubate, body reserves neared depletion on average four days after hatching. During prolonged incubation, females took more frequent and longer recesses. Nest attentiveness consequently decreased, but was still high. In contrast to recesses during normal incubation, during which body mass of the birds decreased, mass remained constant during the recesses of prolonged incubation. The body stores of female eiders seemed to enable them to complete incubation with a limited safety margin. A further drop in body mass is avoided when a critical body mass is reached, because birds then start feeding enough to maintain mass while continuing incubation. Presumably, a similar mechanism will enable eiders to continue incubation when body reserves are prematurely depleted before hatching.     

Patterns of activity and burrow attendance in Cory's Shearwater Calonectris diomedea as revealed by a novel logging technique

We monitored the attendance and activity of Cory's Shearwater Calonectris diomedea on Berlenga Island, Portugal, during the breeding season. To achieve this, we developed a novel logging technique to record the date and time of entrances and departures from the burrows, as well as the identity of each member of a pair. The technique enabled nonintrusive assessment of the activity of burrow-nesting animals over prolonged periods and provided very reliable information. Our study showed that males attended the nests more frequently than females during the pre-laying and chick-rearing periods. We did not find such differences during the incubation period, and both members spent similar amounts of time incubating the eggs. An index of activity (denned as number of entrances plus exits from the nest) achieved higher scores during the pre-laying and incubation periods,
but the activity decreased significantly during the chick-rearing period. We did not find any effect of moonlight on the levels of activity, hour of arrival at the colony or time spent inside the burrows in breeding birds.     

Incubation and brooding performance of the Antarctic Petrel Thalassoica antarctica at Svarthamaren, Dronning Maud Land

Antarctic Petrel Thalassoica antarctica incubation and brooding effort was studied at Svarthamaren, Dronning Maud Land, during the austral summer of 1991–1992. The females probably left the nest site shortly after egg laying. The duration of incubation and brooding shifts as well as the daily weight loss (absolute and proportionate) were comparable with those of other similar-sized procellariform species. Males spent more time incubating and brooding than did females, suggesting higher female energy stress due to egg laying. Incubating birds which were below average weight were likely to desert the nests before their mates returned from feeding trips. Both males and females lost approximately one-fifth of their body-weight during their first incubation shifts. Nevertheless, they increased their initial weights from egg laying to hatching and had their highest initial weights when they returned to start the shift during which the egg hatched. No factors related to adult body-weight explained the duration of the incubation shifts. Both males and females gained weight at a higher rate when at sea than they lost it during incubation, and it is suggested that factors unrelated to food availability or individual feeding skills may be important in regulating the duration of the incubation shifts and the stay at sea.     

Intermittent fasting during winter and spring affects body composition and reproduction of a migratory duck

We compared food intake, body mass and body composition of male and female black ducks (Anas rubripes) during winter (January-March). Birds were fed the same complete diet ad libitum on consecutive days each week without fasting (control; nine male; nine female) or with either short fasts (2 day x week(-1); nine male; nine female), or long fasts (4 day x week(-1); eleven male; twelve female). We continued treatments through spring (March-May) to measure the effect of intermittent fasts on body mass and egg production. Daily food intake of fasted birds was up to four times that of unfasted birds. Weekly food intake of males was similar among treatments (364 g x kg(-1) x week(-1)) but fasted females consumed more than unfasted females in January (363 g x kg(-1) x week(-1) vs. 225 g x kg(-1) x week(-1)). Although both sexes lost 10-14% body mass, fasted females lost less mass and lipid than unfasted females during winter. Total body nitrogen was conserved over winter in both sexes even though the heart and spleen lost mass while the reproductive tract and liver gained mass. Intermittent fasting increased liver, intestinal tissue and digesta mass of females but not of males. Fasting delayed egg production in spring but did not affect size, fertility or hatching of the clutch. Females on long fasts were still heavier than controls after laying eggs. Thus black ducks combine flexibility of food intake with plasticity of digestive tract, liver and adipose tissue when food supply is interrupted during winter. Females modulate body mass for survival and defer reproduction when food supply is interrupted in spring.     

Mate-sharing costs in polygynous Northern Lapwings Vanellus vanellus

In this study bigamous female Northern Lapwings Vanellus vanellus received significantly less incubation relief from their males than monogamous females. On average, monogamous males spent 34.3% of their time incubating and bigamous males 29.9%. Bigamous males divided their effort between their nests, incubating on average 9.4% on primary nests and 20.5% on secondary nests. Bigamous females compensated for the lack of male relief. Primary females incubated for 71.8% of their time, secondary females for 64.2%, while monogamous females spent 52.7% of their time incubating. As a result, there was no significant difference in total nest attentiveness among nests of different status. Primary and secondary females received equivalent incubation relief from the male. Bigamous males increased their contribution to incubation significantly as the season progressed. A bigamous male's distribution of incubation relief between his females was unrelated to female body mass, or to the degree of asynchrony between primary and secondary females in arrival and laying. Incubation time was significantly, negatively, correlated with total nest attentiveness. Monogamous females spent most time, secondary females spent an intermediate time, and primary females spent the least time on maintenance behaviour (foraging, comfort behaviour, inactivity). No significant differences were found in hatching success among females of different mating status. However, the ratio of unhatched to hatched eggs (i.e. the eggs that remained in the nest at the time of hatching) differed significantly: secondary females hatched a smaller proportion of their eggs than monogamous and primary females.     

Variations in adult body mass in roe deer: the effects of population density at birth and of habitat quality

Body mass is a key determinant of fitness components in many organisms, and adult mass varies considerably among individuals within populations. These variations have several causes, involve temporal and spatial factors, and are not yet well understood. We use long-term data from 20 roe deer cohorts (1977-96) in a 2600 ha study area (Chizé, western France) with two habitats contrasting in quality (rich oak forest in the North versus poor beech forest in the South) to analyse the effects of both cohort and habitat quality on adult mass (i.e. median body mass between 4 and 10 years of age) of roe deer (Capreolus capreolus). Cohort strongly influenced the adult body mass of roe deer in both sexes: males born in 1994 were 5.2 kg heavier when aged between 4 and 10 years old than males born in 1986, while females born in 1995 were 4.7 kg heavier between 4 and 10 years old than females born in 1982. For a given cohort, adult males were, on average, 0.9 kg heavier in the rich oak forest than in the poor beech forest. A similar trend occurred for adult females (0.5 kg heavier in the oak forest). The effects of cohort and habitat were additive and accounted for ca. 40% of the variation observed in the adult mass of roe deer at Chizé (males: 41.2%; females: 40.2%). Population density during the spring of the birth accounted for about 35% of cohort variation, whereas rainfall in May-June had no effect. Such delayed effects of density at birth on adult body mass probably affect population dynamics, and might constitute a mechanism by which delayed density-dependence occurs in ungulate populations.     

Female great tits Parus major do not increase their daily energy expenditure when incubating enlarged clutches

Several studies have shown that enlargement of clutches during incubation reduces the long-term survival of parents. In line with these findings, studies on the energetic costs of nocturnal incubation show an increase in energy expenditure with clutch enlargement. Studies on daily energy expenditure during incubation (DEE_inc), however, do not consistently show such a negative effect of clutch enlargement. To determine whether differential survival results from a direct increase in energy costs or rather from costs associated with compensatory behaviour, we studied the DEE_inc (kJ day⁻¹), change in body mass and nest attendance behaviour of free-living female great tits Parus major that incubated either control or experimentally enlarged clutches. DEE_inc did not differ between the two treatment groups, but was negatively related to mean ambient temperature over the 24-h measuring period, and to the fraction of daytime females spent on the nest. Controlling for these two factors, females incubating enlarged clutches did not spend more energy per 24 h period than females incubating control clutches. Clutch enlargement also did not affect body mass of incubating females, or their nest attendance behaviour. Yet, in the enlarged group body mass change and nest attentiveness were negatively correlated, suggesting that females responded differently to the experimental treatment and thereby preventing us from finding an effect of clutch enlargement.     

Parental behaviour of Spanish Imperial Eagles Aquila adalberti: sexual differences in a moderately dimorphic raptor

Capsule The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks.

Aims To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding).

Methods Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences.

Results Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chick-rearing (to feed the chicks). Females were responsible for most of the incubation, nest-building (during incubation and chick-rearing), brooding, shading and feeding of chicks. Nest attendance by females decreased over time. In both sexes, food provisioning increased with brood size.

Conclusion Intersexual differences are discussed in the context of the reversed sexual size dimorphism and parental investment strategies. We suggest that in Spanish Imperial Eagles reversed sexual size dimorphism is best explained by the prey capture difficulty hypothesis, than by parental role division during reproduction.