Variation in egg quality and composition in the Mallard Anas platyrhynchos

Three complete Mallard Anas platyrhyncos clutches from a single site were analysed to determine intra-and inter-clutch variation within and among clutches in quality and composition. Variation between clutches was significantly greater than within clutches in all the examined criteria of egg composition, except for the percentage of water found in yolk. In addition the weight of the yolk was proportional to fresh egg weight. When log transformations were used, the slope of the regression was greater than unity, indicating the proportional contribution of yolk increased respectively with egg weight. A total of 26 eggs from four locations was analysed and no regional variation in egg composition was found but there was variation in egg quality (lipid and protein). The factors affecting the production of a 'good egg' and what in fact is a 'good egg' are discussed. In the Mallard, as in other Anseriformes, it appears that larger eggs may confer a survival advantage to the subsequent young.     

Geographical variation of protein reserves in birds: the pectoral muscle mass of Dunlins Calidris alpina in winter

Pectoral muscle size (as an index of protein reserves) was measured in Dunlins during midwinter on five British estuaries, and examined in relation to latitude and midwinter air temperature. In adults, pectoral muscle size was greater on more northerly and colder estuaries. Pectoral muscle size of juveniles varied less than that of adults between estuaries. For both ages, pectoral muscle size correlations were stronger with temperature than with latitude. The size of protein reserves in the pectoral muscles differed by 26% (adults) and 14% (juveniles) between warmest (Menai Straits) and coldest (Firth of Forth) sites studied. Both pectoralis major and supracoracoideus muscles contributed to the protein store, but the supracoracoideus formed only 12% of the total pectoral muscle mass. The age-difference appeared not to arise through the selective death of some juveniles. We propose that juveniles have a set-point for pectoral muscle size in winter adapted to the broad geographical area within which they may settle. The set-point may then be altered according to the weather conditions experienced at the site where they settle and return as adults.     

Do body condition and plumage during fuelling predict northwards departure dates of Great Knots Calidris tenuirostris from north‐west Australia?

It is often assumed that strong selection pressures give rise to trade-offs between body condition and time in long-distance migrating birds. Birds that are 'behind schedule' in fuel deposition or moult should delay departure, and this should result in a negative correlation between initial condition and departure date. We tested this hypothesis in the Great Knot Calidris tenuirostris migrating from north-west Australia to eastern Asia en route to Siberia. Great Knot gain mass and moult into breeding plumage before leaving northern Australia in late March and early April, and fly 5400–6000 km to eastern China and Korea. We radiotracked 27 individuals (17 males and ten females) to determine departure dates; 23 migrated and four remained in Australia. We characterized body condition at capture using body mass, predicted pectoral muscle mass (based on ultrasound estimates of the size of the pectoral muscles) and breeding plumage scores. Residual condition indices were uncorrelated, indicating that at the individual level, variation in one fuelling component was not strongly associated with variation in the other components. Birds that did not depart had lower residual body mass and breeding plumage indices than those that did migrate; these four birds may have been subadults. Neither sex, size nor the condition indices explained variation in departure date of migrants. Reasons for this are explored. Departure dates for northward migrating waders indicate that the migration window (span over which birds depart) decreases with proximity to the northern breeding grounds. We suggest that migration schedules become tighter as birds get nearer to the breeding grounds. Thus the lack of a relationship between condition and departure date in Great Knots may reflect the fact that the departure episode under study is the first one in sequence and is still 4–8 weeks before breeding.     

Laying date, clutch size and egg size of the Mallard Anas platyrhynchos and Tufted Duck Aythya fuligula

The effect of spring temperature on first egg date, laying period and last clutch date was studied in the Mallard and Tufted Duck. Seasonal clutch size and egg size trends were also examined. In years When Mallard laid early, Tufted Duck also did so. The first Mallard clutch was started earlier and laying period was longer in years with a high mean February temperature. The last clutch was started later in years with a high mean June temperature. In Tufted Duck the laying period increased and the last clutch was started later in years with high mean April temperatures.
Mean hatching date of Mallard clutches was later in years when the date of peak chironomid emergence was late.
In both species, clutch size declined through the season. Egg volume was not related to clutch size in either species, but egg volume in the Tufted Duck declined through the season. No difference in Tufted Duck egg size existed between sites, but the significance of egg size on duckling survival is discussed. Genetic factors related to individual consistency in egg size in Mallard may have obscured egg volume trends during the season because of renesting.     

Dominant black-capped chickadees pay no maintenance energy costs for their wintering status and are not better at enduring cold than subordinate individuals

Winter requires physiological adjustments in northern resident passerines. Cold acclimatization is generally associated with an increase in physiological maintenance costs, measured as basal metabolic rate (BMR), and cold endurance, reflected by summit metabolic rate (M _sum). However, several northern species also form social groups in winter and a bird’s hierarchical position may influence the size of its metabolically active organs as well as its BMR. Winter metabolic performance in these species may therefore reflect a complex set of adjustments to both seasonal climatic variations and social environment. We studied the effect of social status on parameters of cold acclimatization (body mass, size of fat reserves and pectoral muscles, BMR and M _sum) in free-living black-capped chickadees (Poecile atricapillus). Birds that were structurally large and heavy for their body size, mostly dominant individuals, carried more fat reserves and had larger pectoral muscles. However, social status had little effect on metabolic performance in the cold. Indeed, M _sum was independent of social rank while mass-corrected BMR was slightly lower in dominant individuals, likely due to a statistical dilution effect caused by large metabolically inactive fat reserves. BMR and M _sum, whether considered in terms of whole-animal values, corrected for body mass or body size were nevertheless correlated, suggesting a functional link between these metabolic components. Our results therefore indicate that the energy cost of social dominance is not a generalized phenomenon in small wintering birds.     

Phenotypic flexibility of a southern African duck Alopochen aegyptiaca during moult: do northern hemisphere paradigms apply?

Phenotypic flexibility during moult has never been explored in austral nomadic ducks. We investigated whether the body condition, organ (pectoral muscle, gizzard, liver and heart) mass and flight‐feather growth Egyptian geese Alopochen aegyptiaca in southern Africa show phenotypic flexibility over their 53‐day period of flightless moult. Changes in body mass and condition were examined in Egyptian geese caught at Barberspan and Strandfontein in South Africa. Mean daily change in primary feather length was calculated for moulting geese and birds were dissected for pectoral muscle and internal organ assessment. Mean body mass and condition varied significantly during moult. Body mass and condition started to decrease soon after flight feathers were dropped and continued to do so until the new feathers were at least two‐thirds grown, after which birds started to regain body mass and condition. Non‐moulting geese had large pectoral muscles, accounting for at least 26% of total body mass. Once moult started, pectoral muscle mass decreased and continued to do so until the flight feathers were at least one‐third grown, after which pectoral muscle mass started to increase. The regeneration of pectoral muscles during moult started before birds started to gain overall body mass. Gizzard mass started to increase soon after the onset of moult, reaching a maximum when the flight feathers were two‐thirds grown, after which gizzard mass again decreased. Liver mass increased significantly as moult progressed, but heart mass remained constant throughout moult. Flight feather growth was initially rapid, but slowed towards the completion of moult. Our results show that Egyptian geese exhibit a significant level of phenotypic flexibility when they moult. We interpret the phenotypic changes that we observed as an adaptive strategy to minimize the duration of the flightless period. Moulting Egyptian geese in South Africa undergo more substantial phenotypic changes than those reported for ducks in the northern hemisphere.     

Intra-individual variation in body temperature and pectoral muscle size in nestling Alpine swifts Apus melba in response to an episode of inclement weather

The Alpine swift (Apus melba) forages on insects caught exclusively on the wing, implying that dependent nestlings face acute food shortage in periods of cold and rainy weather. Therefore, there should be strong selection on nestling swifts to evolve physiological strategies to cope with periods of undernutrition. We have investigated intra-individual changes in nestling pectoral muscle and body temperature in response to a 1-week period of inclement weather. The pectoral muscle is the largest reserves of proteins, and nestlings have to devote a large amount of energy in the maintenance of body temperature. The results show that nestling pectoral muscle size and body temperature were significantly reduced during the episode of inclement weather. Assuming that these physiological changes are adaptive, our study suggests that nestling swifts spare energy by a pronounced reduction (up to 18°C) in body temperature and use proteins from the pectoral muscle as a source of extra energy to survive prolonged periods of fasting.     

Sex, diet and feeding method-related differences in body condition in the Oystercatcher Haematopus ostralegus

Measurements were made of Oystercatcher corpses to find the most reliable measure of body condition in live birds. Total body weight was as accurate as muscle thickness in assessing the weight of the pectoral muscles, a major store of protein reserves. Total body weight was also a good indicator of fat reserves. Wing‐length was the most reliable measure of body size. Body condition in live birds was measured as an individual's residual weight derived from a general linear model of (loge) body weight against age, month, (loge) wing‐length and time since capture. On the Exe estuary in autumn, there was no significant difference in body condition between same‐age Oystercatchers of different diets and feeding methods. In the winter months, however, body condition differed significantly between mussel feeders using different feeding methods, and between mussel feeders and birds that fed on worms and clams. Differences between diet/feeding methods were not the same for each age group. Birds with the highest mean body condition index in adults were mussel hammerers, in immatures mussel stabbers and in juveniles, worm/clam feeders. No significant difference in body condition was found between the sexes in any age group in autumn. In winter, when birds with the same diet/feeding method were considered, females were significantly heavier than males. However, when birds of all diets and feeding methods were combined, weight differences between the sexes were not apparent. We examine reasons why birds with certain diets and feeding methods may be heavier than others in winter, and why females are sometimes heavier than males. We conclude that, in most cases, it is due to differences between birds in their ability to achieve a common target weight. However, we conclude that adult females try to achieve a higher target weight than males, probably as a premigratory and prebreeding strategy. In the light of this, we consider the consequences for adult females, in terms of reproductive success and survival, of specializing in diets and feeding methods associated with lower body weights in winter.     

An improved technique for estimating pectoral muscle protein condition from body measurements of live gulls

Body measurements, which could be taken from live birds, were used to estimate total pectoral muscle protein in Lesser Black-backed Gulls Larus fuscus. The maximum cross-sectional area of the flight muscles was measured from the profile of the muscle surface over the keel, and this was used in conjunction with the length of the flight muscle to estimate muscle volume. The estimate of muscle volume was then used with fresh body weight to estimate total flight muscle protein. A highly significant correlation was found between the estimated values and actual pectoral muscle protein mass determined by carcass analysis. The model developed from the source group was then validated using a second independent sample, in which flight muscle protein was estimated from the model. Carcass analysis again demonstrated a good correlation between estimated and actual total protein. Different methods of controlling for body-size to calculate protein condition from measures of total protein were considered. The technique described here provides a simple and reliable method of estimating pectoral muscle protein condition in live gulls which could be applied to studies of body condition in other species.     

Body condition changes of sand martins (Riparia riparia) during breeding, and a comparison with fledgling condition

The body condition of adult sand martins during the breeding season and a sample of fledglings was investigated by carcass analysis and by examination of live birds in the field. Fat scoring of live individuals was a reliable predictor of an individual's lipid content in most instances. Body mass changes during breeding were related to changes in the size of birds' lipid reserves, pectoral muscle mass, body water, and to development of the reproductive system. In both males and females, reserve lipid declined between the onset of breeding and nestling rearing. Pre-breeding males had significantly greater pectoral muscle masses than did nestling rearing females. The potential significance of protein in pectoral muscles as an energy reserve during breeding was small compared with lipid reserves. By comparing potential energy reserves in body lipid and protein with daily energy expenditure, it was calculated that neither incubating nor nestling rearing adults could survive a day of normal activity without feeding. The selective premium on adults optimizing their use of time and energy for self-maintenance behaviour during breeding is therefore likely to be great.     

Sex differences in body composition of wintering Mallards (Anas platyrhynchos): possible implications for survival and reproductive performance

Capsule Wintering female Mallards have a higher fat load than males which may compensate for their lower body size and ultimately improve their fitness.

Aims To investigate whether sex-related differences in biological processes in winter are associated with differences in body nutrient storage and flight capabilities and, if so, the possible implications for survival and reproductive performance.

Methods We analysed the body composition and the flight parameters of 35 male and 35 female Mallards wintering in western Europe on the Rhine river.

Results Males were 15% heavier and 18% larger than females, but the latter carried 27% more fat per unit body mass. Relative to body lipid mass, body protein mass was 11% lower for females. Wing loading was 7% lower in females and power loading was similar in both sexes.

Conclusions High lipid mass gives females survival capabilities to food shortage similar to males. This helps sustain them through their prebasic moult and breeding success. Heavier muscles in males compensate for their higher wing loading and thus improve pairing success. Wintering and reproductive strategies in Mallard seem to be closely linked through body reserves.     

Low survival after release into the wild: assessing “the burden of captivity” on Mallard physiology and behaviour

Captive-reared animals used in reinforcement programs are generally less likely to survive than wild conspecifics. Digestion efficiency and naive behaviour are two likely reasons for this pattern. The Mallard is a species with high adaptability to its environment and in which massive reinforcement programs are carried out. We studied physiological and behavioural factors potentially affecting body condition and survival of captive-reared Mallards after being released. Digestive system morphology and an index of body condition were compared among three groups: captive-reared birds remaining in a farm (control), captive-reared birds released into the wild as juveniles (released) and wild-born birds (wild). We also compared behaviour and diet of released vs. wild Mallards. Finally, we conducted a 1-year survival analysis of captive-reared birds after release in a hunting-free area. Gizzard weight was lower in control Mallards, but the size of other organs did not differ between controls and wild birds. The difference in gizzard weight between released and wild birds disappeared after some time in the wild. Diet analyses suggest that released Mallards show a greater preference than wild for anthropogenic food (waste grain, bait). Despite similar time-budgets, released Mallards never attained the body condition of wild birds. As a consequence, survival probability in released Mallards was low, especially when food provisioning was stopped and during harsh winter periods. We argue that the low survival of released Mallards likely has a physiological rather than a behavioural (foraging) origin. In any case, extremely few released birds live long enough to potentially enter the breeding population, even without hunting. In the context of massive releases presently carried out for hunting purposes, our study indicates a low likelihood for genetic introgression by captive-reared birds into the wild population.     

Evidence of climate change effects on within‐winter movements of European Mallards Anas platyrhynchos

Other than during periods of migration, animal movement tends to be poorly described, despite the potential importance of such movements, which may prove crucial for surviving periods of bad weather and low food availability. We analysed within‐winter (December–February) movements of Mallard using the EURING Data Bank. Most movements were directed towards the south or southwest during all three winter months. Distances covered increased with winter harshness and generally decreased from 1952 to 2004. Mallards appear to move less than other duck species during winter. Long‐distance movements of Mallards seem to be related to cold weather, birds only moving long distances in large numbers during the very coldest winters. Movements are not restricted during midwinter, but occur throughout the winter. The decreasing within‐winter movement over time (1952–2004) could be explained by decreasing reporting probabilities and/or warmer winters in recent decades. However, the first is only true if the decrease in reporting probability increases with distance moved, for which we found no indication in our study. Therefore, we suggest that the pattern found is evidence of long‐term winter warming reducing the distance of within‐winter movements in this species.     

Direct and indirect effects of winter harshness on the survival of Mallards Anas platyrhynchos in northwest Europe

To understand population dynamics it is necessary to understand vital rates, which may be affected by a wide range of factors including environmental variables such as weather. Weather conditions can affect birds’ vital rates directly through increased mortality due to impaired conditions, or indirectly via changes in body condition and/or behaviour. Most understanding of direct and indirect effects of weather comes from studies of breeding birds, whereas the situation in non‐breeding periods is less clear. Here, we analysed annual survival of non‐breeding Mallard Anas platyrhynchos, the most hunted waterfowl species in Europe, and assessed whether survival is related directly to winter harshness and/or indirectly via changes in winter recovery distributions. Recovery data on Mallards, initially marked in southeast Sweden, were analysed with an information‐theoretic approach using program mark . Over 10 000 Mallards were marked in two time periods, 1964–1982 and 2002–2008, of which 13.3 and 4.7%, respectively, were later recovered. Mallards had lower annual survival in the early trapping period (0.58–0.63) than in the later period (0.69–0.71), with no clear effects of sex, age or year. Within each study period, winter harshness did not directly correlate with survival. However, milder winters may have contributed indirectly to higher survival in the second period, as winter harshness data were correlated with the distances to recovery positions for females, and also because winter recovery areas have shifted northeast during the past decades, possibly indicating a shortened migratory distance. Migration is costly, and there is therefore a likely linkage between migration behaviour and survival of dabbling ducks, in which direct as well as indirect effects of winter harshness may play a role. Other factors, such as hunting pressure, are also likely to have changed in the past decades, and may also have contributed to improved survival of Mallards in northwest Europe.     

Myoglobin levels and mATPase activity in pectoral muscles of spruce and ruffed grouse (Aves: Tetraoninae)

Myoglobin concentration and myosin ATPase activity were measured in the pectoral muscle of wild spruce grouse (Dendragapus canadensis) and ruffed grouse (Bonasa umbellus), together with the weight of the Mm. pectoralis, supracoracoideus and heart. mATPase activities were similar in both species, but spruce grouse contained 15 times more myoglobin in the pectoralis muscle and the heart was three times heavier than that of the ruffed grouse. The relative mass of the flight muscles and wing loading were similar between species. Characteristics of the pectoral muscle of both grouse species reflect adaptations to predation and advertising displays. The glycolytic nature of the ruffed grouse pectoral muscle and small heart size is an adaptation to a sedentary existence within a small home range. The more oxidative pectoral muscle of spruce grouse together with its larger heart are adaptations to seasonal dispersals requiring more sustained flight.     

Short- and long-term effects of winter and spring weather on growth and survival of red deer in Norway

Populations of red deer (Cervus elaphus) in Norway have increased continuously over the last decades. We tested the possible effects of climate and increase in population size on the survival rates and body condition of individuals in one of the northernmost populations of red deer in Europe. Based on 678 individuals of known age marked between 1977 and 1995, we estimated annual survival rates, the probabilities of being harvested and the recapture probability according to sex, age, year, winter and spring weather, population size, and, body weight and body condition, using capture-mark-recapture models. Winter harshness negatively influenced the body weight of yearlings and the survival of calves of both sexes. Spring weather influenced the survival of males in all age classes. A negative trend during the study period was detected in body weight and condition of calves and yearlings, but not in any age- or sex- specific survival rates. No significant gender differences in mean survival were shown in any age class. Moreover, there was little (male) or no (female) detectable between-year variation in survival rates for yearlings and adults. Winter weather acts as a limiting factor on population growth through a short-term effect on first-year survival and a long-term effect on body weight. We discuss the surprising low sex differences in natural survival rates and the differential effects of winter harshness on body weight, body condition and survival in relation to life history characteristics of red deer. Received: 10 November 1997 / Accepted: 2 June 1998     

Effects of experimentally increased egg production on female body condition and laying dates in the great skua Stercorarius skua

We investigated the effects of increased egg production on body condition as well as on measures of reproductive performance in great skuas, Stercorarius skua, over two subsequent years. We experimentally increased egg production from the normal two to six eggs. Six eggs might also be produced under natural circumstances after repeated clutch loss. After the production of the last egg we measured: (i) body mass, (ii) pectoral muscle, and (iii) haematocrit, total red blood cell count and mean corpuscular volume, as indicators of body condition. We took the same measurements of control females who had produced the normal clutch of two eggs. The measurements were repeated one year after the manipulation, and survival, laying dates, clutch sizes and hatching success were recorded for up to three consecutive years. After producing six eggs, females were lighter, had smaller pectoral muscles and lower haematological values than control females. Hatching success of eggs was significantly reduced. Even one year after the experiment there were still differences in body condition. Annual survival was not affected by the manipulations, although there was an indication that survival costs depended on whether chicks were raised after the increased egg production. While pair bonds and egg sizes were not affected in the post‐experimental year, females started breeding significantly later than in the previous year. Two years after the experiment laying dates had advanced again and were not different from those of control females. This pattern of maintaining survival and egg sizes, but delaying breeding in the post‐experimental year was found for two independent groups of females which had both been subjected to increased egg production. These results present evidence that increased egg production can have long‐term effects on female body condition and aspects of reproduction. However, although present, the costs of extra eggs appear to have been relatively small in the great skua in comparison to the two other bird species for which inter‐annual effects have been reported.     

The rôle of fat and protein during breeding in the White-bellied swiftlet (Collocalia esculents)

The breeding biology of the White-bellied swiftlet was studied in Malaysia. Birds were captured every month, and more intensively during the breeding season. To investigate the role of fat and protein reserves in the annual cycle, carcasses were fat extracted after separating the pectoral muscles. The stage of the laying cycle was investigated by histological examination of the ovaries.
Fat and protein reserves were correlated with the body size of the birds. In non-laying females and males, both reserves were correlated with date and feeding conditions determined by the weather. In egg-laying birds, protein reserves were again correlated with feeding conditions, but fat reserves were negatively correlated with the day of the laying cycle. Assessment of the daily foraging abilities of the birds showed that, for egg-layers, proteins were likely to be in greatest supply and fats in least supply. It is suggested that a fat reserve serves as an insurance against poor feeding conditions for laying birds.     

Habitat use and its implications to functional morphology: niche partitioning and the evolution of locomotory morphology in Lake Tanganyikan cichlids (Perciformes: Cichlidae)

Animal locomotory morphology, i.e. morphological features involved in locomotion, is under the influence of a diverse set of ecological and behavioral factors. In teleost fish, habitat choice and foraging strategy are major determinants of locomotory morphology. In this study, we assess the influence of habitat use and foraging strategy on important locomotory traits, namely the size of the pectoral and caudal fins and the weight of the pectoral fin muscles, as applied to one of the most astonishing cases of adaptive radiation: the species flock of cichlid fishes in East African Lake Tanganyika. We also examine the course of niche partitioning along two main habitat axes, the benthic vs. limnetic and the sandy vs. rocky substrate axis. The results are then compared with available data on the cichlid adaptive radiation of neighbouring Lake Malawi. We find that pectoral fin size and muscle weight correlate with habitat use within the water column, as well as with substrate composition and foraging strategies. Niche partitioning along the benthic–limnetic axis in Lake Tanganyikan cichlids seems to follow a similar course as in Lake Malawi, while the course of habitat use with respect to substrate composition appears to differ between the cichlid assemblages of these two lakes.     

Allometric dependences of oxygen transport parameters in skeletal muscles during ontogenesis of domestic fowl

In domestic fowl, from day 10 of embryogenesis to six month of postnatal life, investigation into the white glycolytic pectoral and red oxidative gastrocnemius muscles allometric dependences of the structural and functional parameters providing muscular fibres by oxygen: speed of breath of an isolated muscular fibre, size of a surface of an external membrane of mitochondria in a fibre, its permeability to oxygen, density of the capillaries located around of a fibre and in all muscle, volumetric speed of a muscular blood flow, and connection of speed of breath of muscular fibres with weight of a body of a bird.