A physiological basis for colony desertion by Red-billed queleas (Quelea quelea)

A breeding colony of Red-billed queleas, established in N.E. Nigeria under poor feeding conditions occasioned by drought, was abandoned after the eggs had been laid. Inadequate energy intake caused males to leave before completing the nests. This resulted in thousands of eggs being laid through bottomless nests onto the ground. The females left progressively as they completed their clutches; below normal protein- and fat-reserves probably combined to induce abandonment. Some individuals, predominantly females, died on the last night of occupation. Death apparently resulted from an adverse nutritional balance at a crucial stage in the laying sequence. The main value of the fat reserves in females beginning to lay appears to be in allowing maximal foraging "for protein".     

Mean corpuscular volume (MCV) as a measure of condition in birds

Haematological parameters, particularly haematocrit, are frequently used in assessing condition in birds. Mean corpuscular volume (MCV) overcomes some of the drawbacks associated with measuring haematocrits and therefore should be a better condition index. We investigated the relationship between these blood parameters and the breeding performances of great skuas Catharacta skua . As predicted from activity budgets of the sexes, male MCVs were significantly positively correlated with hatch date and the MCVs of both sexes were negatively correlated with the number of chicks fledged. No correlations existed between these breeding parameters and haematocrit. Since males provision females and chicks, they probably influence breeding performance via foraging abilities, whereas in females nutritional investment may be more important. This is the first study of a free-living/nondomesticated vertebrate population in which these kinds of relationship have been demonstrated and we conclude that MCV is a useful measure of condition.     

Endogenous reserve dynamics of northern common eiders wintering in Greenland

Endogenous reserves influence both survival and reproduction of many waterfowl species, but little is known about reserve levels of most species during the nonbreeding season, particularly those wintering at high latitudes. We investigated whether age, sex, and season were related to carcass composition of northern common eiders (Somateria mollissima borealis) wintering in southwest Greenland during 1999–2002. Adults carried more lipid and protein than juveniles during all winters. Among both age classes, males and females had similar fat levels but males carried slightly more protein. There was no dramatic seasonal variation in lipid or protein content. This suggests that during the period of this study, these eiders did not experience large-scale nutritional shortfalls. As predicted, Greenlandic eiders carried more lipid reserves than eider populations wintering in more temperate environments. Contrary to prediction, there was little relation between reserve levels and photoperiod, ambient temperature, or hunting disturbance intensity. Our results suggest that both sexes are equally capable of dealing with nutritional deficits, and that juvenile birds are more prone to nutritional stress as evidenced by their consistently poorer body condition.     

Assessing the effects of haematophagous ectoparasites on the health of nestling birds: haematocrit vs haemoglobin levels in House Wrens parasitized by blow fly larvae

We compared haematocrits and blood haemoglobin concentrations of nestling House Wrens Troglodytes aedon in nests with relatively large numbers of haematophagous larvae of the blow fly Protocalliphora parorum (>6.4 large larvae/nestling) and nests in which exposure to larvae was severely reduced or eliminated (0–2.0 larvae/nestling). Heavily parasitized nestlings showed no reduction in haematocrit levels but a significant 28% reduction in haemoglobin levels. Previous research on avian response to chronic blood loss suggests that parasitized nestlings may show normal volumes of red blood cells as a result of a rapid production of new cells in response to blood loss and, additionally, as a result of swelling of individual cells left in the bloodstream after parasite feeding. Rapid erythropoiesis places high numbers of haemoglobin-poor, immature cells into the bloodstream which would explain the reduced haemoglobin levels of parasitized nestlings. Our results refute the conclusion that larval feeding has "little direct effect" on nestling wrens in this parasite–host system, drawn earlier by Johnson and Albrecht (1993) based on examination of haematocrits alone. Our results also strongly suggest that researchers wanting to measure effects of blood-feeding parasites on birds measure haemoglobin levels, not haematocrits.     

Influence of fibrinogen and haematocrit on erythrocyte sedimentation kinetics

This study investigates the influence of haematocrit, fibrinogen concentration and fibrinogen availability (amount of fibrinogen per red blood cell) on erythrocyte sedimentation. The Westergren technique was applied to blood samples from 36 subjects and to their blood manipulated to haematocrits of 10, 20, 30 and 40%. Readings were taken every 10 minutes for 300 minutes. Previous studies indicate that erythrocyte sedimentation occurs in three phases. In this study, we show that haematocrit has little influence on either the rate of fall of particles in the first phase (m1) or the duration of the first phase. This is also true for fibrinogen availability and for fibrinogen concentration at low haematocrits. At high haematocrits m1 increases with fibrinogen concentration. The rate of fall of rouleaux during phase 2 (m2) and ESR60 both decrease exponentially with haematocrit and increase linearly with fibrinogen concentration. While m2 is more closely correlated to fibrinogen availability than to fibrinogen concentration or to haematocrit, this is not the case for ESR60. Thus haematocrit, fibrinogen concentration and fibrinogen availability are more important to the velocity of sedimentation in the second phase than to the sedimenting velocity during phase 1 or to the duration of phase 1.     

Female-dependent stenogamy in the mosquito, Aedes taeniorhynchus

A female-dependent stenogamous condition was found in the mosquito, Aedes taeniorhynchus. When confined in cages, males attempted with similar frequencies to mate with wild and colony females. Wild females remained uninseminated because they actively prevented firm genital union. During simulated sunsets, swarming flights of colony males began at higher light intensities than those of wild males, and throughout these sunsets many more colony males participated in swarming than did wild males. Nevertheless, wild and colony males did not differ in their mating effectiveness. Both kinds of males were highly successful in transferring sperm to colony females, yet most of their attempted matings with wild females ended in failure. Autogeny occurred in stenogamic colony females and in eurygamic wild females.     

Proximate causes and fitness consequences of hatching failure in lesser kestrels Falco naumanni

Hatching failure is a pervasive phenomenon in birds, but factors affecting hatchability remain poorly understood. We studied proximate causes and fitness consequences of hatching failure in a long‐monitored population of the colonial lesser kestrel Falco naumanni. We investigated whether hatchability was related to clutch characteristics, parental traits, and social or environmental features. Hatching failure represents a cost for the parents in terms of immediate fitness, since it reduced both their number of young fledged and recruits in the breeding population, even when controlling for clutch size. Hatching failure showed a non‐linear relationship with clutch size, clutches of four eggs showing higher levels of hatching success than larger or smaller clutches. Hatchability could therefore play a role in the evolution of optimal clutch size in this species, at least constraining the maximum number of eggs the parents can afford to incubate. Contrary to most studies, the mean volume of the clutch and the individual egg volume were negatively related to hatching failure, indicating that large eggs have thermoregulatory and/or nutritional advantages. Mean daily maximum temperature during incubation affected hatching success negatively, but only for females in poor condition. This result seems to indicate that females are reluctant to jeopardize their own condition, but instead sacrifice incubation effort by paying the costs of a lower hatching success in circumstances of high temperatures. There was no evidence that hatching failure was related to the intrinsic properties of individuals or genetic similarity between the parents as indicated by low repeatabilities of: (1) males that bred with different females, (2) females that bred with different males, and (3) pairs breeding together in different years. Neither colony size nor subpopulation size affected hatchability. All these findings show how hatching failure is simultaneously influenced by several factors acting in a complex way, which could in part explain the apparently conflicting conclusions of empirical or even experimental studies carried out to date.     

Nutritional status of Efe pygmies and Lese horticulturists

We assessed the nutritional status of 90 pygmies (Efe) and 211 members of a neighboring horticultural Lese in the Ituri forest in northeast Zaire. Clinical signs of iron and iodine deficiency were highly prevalent, but the frequency of these and other clinical signs of nutritional deficiency did not differ between the two groups. Infectious diseases such as yaws, cellulitis, and filiariasis were common. Absolute heights and weights of both Efe males and females aged 2–18 years were less than the 5th percentile of the National Center for Health Statistics standards. Weights for height of both groups were within the normal range. Weights and heights, expressed as percentages of the 50th percentile for age and sex, were significantly lower (P < .001) in Efe males and females than among Lese males and females, but weights for height did not differ significantly. Z-Scores of height and weight were also significantly lower in Efe males and females than among their Lese counterparts. The differences in weight and height, expressed either as a percentage of the 50th percentile or as Z-scores, were most apparent in older adolescents and persisted among adults. The normal weight for height among both populations indicated that acute undernutrition did not exist at the time of the survey. Despite comparable levels of adult fatness, measured by triceps skinfold thickness, heights of Efe males and females were lower than those of the Lese. These observations support the hypothesis that genetic differences account for the short stature of the Ituri pygmy. However, because the environments shared by the two groups are not identical and because other practices differ, nutritional effects cannot be excluded.     

Fat is sexy for females but not males: the influence of body reserves on reproduction in snakes (Vipera aspis)

Reproduction is energetically expensive for both sexes, but the magnitude of expenditure and its relationship to reproductive success differ fundamentally between males and females. Males allocate relatively little to gamete production and, thus, can reproduce successfully with only minor energy investment. In contrast, females of many species experience high fecundity-independent costs of reproduction (such as migration to nesting sites), so they need to amass substantial energy reserves before initiating reproductive activity. Thus, we expect that the relationship between energy reserves and the intensity of reproductive behavior involves a threshold effect in females, but a gradual (or no) effect in males. We tested this prediction using captive vipers (Vipera aspis), dividing both males and females into groups of high versus low body condition. Snakes from each group were placed together and observed for reproductive behavior; sex-steroid levels were also measured. As predicted, females in below-average body condition had very low estradiol levels and did not show sexual receptivity, whereas males of all body condition indices had significant testosterone levels and displayed active courtship. Testosterone levels and courtship intensity increased gradually (i.e., no step function) with body condition in males, but high estradiol levels and sexual receptivity were seen only in females with body reserves above a critical threshold.     

Haematocrit correlates with tail ornament size in three populations of the Barn Swallow (Hirundo rustica)

1. Handicap models of sexual selection propose that male ornaments are indicators of male quality and that honesty is enforced by the costs imposed by the exaggerated ornamental traits. In long-distance migratory birds that feed on the wing, the aerodynamic cost of exaggerated ornamental characters should be particularly high because the size of the ornaments deviates from the natural selection optimum. During migration, birds are expected to raise their oxygen consumption in relation to the energetic demands imposed by their morphology. An increase of haematocrit is an adaptive response to enhance oxygen uptake and efficiency of transfer to the muscular tissues during spells of intense muscular activity.
2. The change of haematocrit of Barn Swallows ( Hirundo rustica ) after their arrival to the breeding sites, and the relationships between haematocrit values recorded after migration and the size of ordinary and sexually selected morphological characters in three Barn Swallow populations were analysed.
3. Males had higher haematocrit values than females. Individual haematocrit values declined after arrival to the breeding sites. Haematocrit values of males were significantly and positively correlated with the size of their ornamental tail but not correlated with other characters, thus suggesting that well-ornamented males, in order to arrive early, have to raise their haematocrit above the level of short-tailed males.
4. Males and females of similar tail length did not differ in their haematocrit, thus suggesting that sexual dimorphism in haematocrit might be functionally related to dimorphism in tail length.
5. Our results are consistent with the handicap principle because long-tailed males experience lower mortality and larger seasonal reproductive success compared with short-tailed males.     

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.     

Competing females and caring males. Sex steroids in African black coucals, Centropus grillii

The black coucal is the only known altricial bird species in which females mate with and lay eggs for more than one male and males are responsible for all parental care (classical polyandry). In this species, the left testis is atrophied and it has been speculated that this may result in a reduction of circulating androgens, providing a unique mechanism for reversals in sex roles. We therefore investigated whether there is a reversal in circulating androgens and oestrogens in black coucals. Despite the reversals in sex roles, males had significantly higher levels of plasma testosterone than females, in a pattern typical of that of monogamous male passerines. Testosterone levels of both sexes were higher during the mating than during the premating stage and were low in males during the nestling stage. The concentrations of androstenedione, dehydroepiandrosterone and oestradiol did not differ between the sexes and were generally low. A physiological challenge with gonadotropin-releasing hormone (GnRH) resulted in a significant increase in testosterone in males but not in females, suggesting either that females are not responsive to GnRH or that they express patterns of testosterone that are similar to those of males of species with a polygynous mating system without paternal care, in which testosterone is expressed at maximum levels throughout the breeding season. We conclude that the absence of one testis does not provide a mechanism for sex role reversal in black coucals. Either androgens are not involved in the regulation of male-like traits in females or females are sensitive to relatively low levels of these steroids.     

Intersex and interspecies differences in sucrose consumption by rats with various behavioral strategies]

Sucrose consumption by male and female rats during active avoidance acquisition was measured in two rat strains: KLA (Koltushi low avoidance) and KHA (Koltushi high avoidance) selected for divergent performance in a shuttlebox. Under resting condition, there were no interstrain difference in sucrose consumption by males, but KHA females consumed significantly less sucrose than KLA females. Active avoidance acquisition during five consecutive days decreased sucrose consumption in KLA males and did not change sucrose consumption in KHA males. Within a week after exposure to the stress, the sucrose consumption by KLA males returned to its normal values, and KHA males consumed significantly more sucrose. The active avoidance conditioning did not affect sucrose consumption in females of both strains. Substitution of 32% solution for 4% produced on the first day a sharp decrease in sucrose consumption in males of both strains, while females sharply increased consumption of the diluted solution over the next four days of observation. During this time, males returned to consumption of the same volume of the solution despite its decreased concentration. The findings suggest that the exposure to the escapable stress induces the negative affect only in KLA males.     

Behaviour of one-year-old rhesus monkeys in a strange situation

When one-year old rhesus monkeys and their mothers were removed from the colony to a strange situation, infants' activity was initially low compared with behaviour six days later. Although absolute values did not differ between males and females, correlations did. That is, three days after return to the colony, correlations with baseline colony behaviour were significantly positive for females, while males had one significantly negative correlation. On the other hand, males had more significant correlations than females when behaviour in the strange situation was correlated with colony scores. Of the six individuals that had adverse early experience, five showed extreme behaviour. The exception was CT, son of a female with a very low ‘excitable’ score. In fact for all males, mothers' colony scores were significantly correlated with sons' behaviour in the strange situation.     

Food supplementation and possible mechanisms underlying early breeding in the Florida Scrub-Jay (Aphelocoma coerulescens)

Food supplementation studies demonstrate the importance of resources in the timing of reproduction. Studies of Florida Scrub-Jays (Aphelocoma coerulescens) found that supplemented jays bred earlier than unsupplemented jays and that protein may play a critical role. In this study, free-living scrub-jays were provided with supplemental diets high in fat and protein (HFHP) or high in fat and low in protein (HFLP). Jays in both treatments bred earlier than unsupplemented controls (CNT), but HFHP-supplemented jays bred earlier than HFLP jays. To assess possible mechanisms, we measured testosterone (T) in males, estradiol (E2) in females, and corticosterone (CORT) in both. HFHP males had higher T than HFLP and CNT males, but treatment did not affect E2 levels of females. Pilot studies of scrub-jays in suburban environments suggest that the spatial and temporal predictability of food may influence corticosterone (CORT) levels. Suburban jays have year-round access to human-provided foods and breed earlier than wildland jays; thus, we compared CORT in all treatments in the natural site (wildlands) with those of suburban jays. CORT levels of suburban jays were lower than HFLP, HFHP, and CNT jays. HFHP-supplemented jays had lower CORT levels than those of HFLP and CNT jays. The observed differences in the timing of breeding, both between suburban and wildland populations and between experimental groups in the wildlands, may result from differences in the spatial and temporal predictability of food, and the nutritional differences in diets. Because CORT can negatively affect the reproductive axis, we postulate that nutrient availability, the predictability of food, CORT levels, and initiation of reproduction are inextricably linked.     

Endocrine correlates of parental care in an Antarctic winter breeding seabird, the emperor penguin, Aptenodytes forsteri

Plasma levels of luteinizing hormone (LH) and prolactin associated with parental behavior were measured in the Antarctic winter breeding emperor penguin, Aptenodytes forsteri. Males exclusively incubate the egg while females exclusively brood the nonhomeothermic young; both sexes alternate in rearing the homeothermic young. Birds were sampled on arrival from the sea through egg laying, incubation, and brooding. All parent birds lost their chicks at the end of the brooding period due to harsh weather but sampling continued. In females, LH titers dropped after egg laying but levels were restored when the birds returned from the sea to brood the chicks and were not depressed by high prolactin levels. Plasma prolactin remained low in males captured on arrival and kept until the free-living males finished incubation. In breeders, prolactin secretion increased during the prelaying period when day length decreased. Prolactin levels stayed elevated in males during incubation and in brooding females returning after a 2-month absence at sea. Prolactin values were higher in brooding females than in males ending incubation or returning in late brooding. These levels did not drop after chick loss, and the sexual difference in prolactin values was maintained after breeding failure. In emperor penguins, increased prolactin secretion appears to be triggered around the time of egg laying and continues, driven by an endogenous mechanism, through incubation and brooding until rearing is completed. Prolactin secretion independent of external stimuli may have evolved in pelagic seabirds to maintain parental care despite long absences at sea from the breeding colony.     

Should I stay or should I go? Hormonal control of nest abandonment in a long-lived bird, the Adélie penguin

According to life-history theory, long-lived birds should favor their survival over the current reproductive attempt, when breeding becomes too costly. In seabirds, incubation is often associated with spontaneous long-term fasting. Below a threshold in body reserves, hormonal and metabolic shift characteristics of a switch from lipid to protein utilization (phase III, PIII) occur. These metabolic changes are paralleled by nest abandonment and stimulation of refeeding behavior. Parental behavior is then under control of two hormones with opposite effects: corticosterone (CORT) and prolactin which stimulate foraging and incubation behavior, respectively.The aim of this study was to determine the respective role of these two hormones in nest abandonment by Adélie penguins. To this end, plasma hormone levels were measured before egg-laying and at departure from the colony (i.e. when birds were relieved by their partner or abandoned their nest), and related to nutritional state and incubation success.We found that males abandoning their nest in PIII presented high CORT levels and low prolactin levels. Interestingly, males which presented high plasma levels of prolactin in PIII did not abandon. We show that although CORT is the first hormone to be affected by prolonged energy constraints, the combined effects of high CORT and low prolactin levels are necessary for parents to favor self-maintenance and abandon the nest. We provide insights into time-course changes of the endocrine profile as PIII proceeds and report that reaching proteolytic late fasting is not sufficient to induce nest abandonment in a long-lived bird.     

Should I stay or should I go? Hormonal control of nest abandonment in a long-lived bird,the Adélie penguin

According to life-history theory, long-lived birds should favor their survival over the current reproductive attempt, when breeding becomes too costly. In seabirds, incubation is often associated with spontaneous long-term fasting. Below a threshold in body reserves, hormonal and metabolic shift characteristics of a switch from lipid to protein utilization (phase III, PIII) occur. These metabolic changes are paralleled by nest abandonment and stimulation of refeeding behavior. Parental behavior is then under control of two hormones with opposite effects: corticosterone (CORT) and prolactin which stimulate foraging and incubation behavior, respectively.The aim of this study was to determine the respective role of these two hormones in nest abandonment by Adélie penguins. To this end, plasma hormone levels were measured before egg-laying and at departure from the colony (i.e. when birds were relieved by their partner or abandoned their nest), and related to nutritional state and incubation success.We found that males abandoning their nest in PIII presented high CORT levels and low prolactin levels. Interestingly, males which presented high plasma levels of prolactin in PIII did not abandon. We show that although CORT is the first hormone to be affected by prolonged energy constraints, the combined effects of high CORT and low prolactin levels are necessary for parents to favor self-maintenance and abandon the nest. We provide insights into time-course changes of the endocrine profile as PIII proceeds and report that reaching proteolytic late fasting is not sufficient to induce nest abandonment in a long-lived bird.     

A Dry Summer Diminishes Mate Search Effort by Pronghorn Females: Evidence for a Significant Cost of Mate Search

In the 2 weeks before estrus, pronghorn (Antilocapra americana) females on the National Bison Range in northwestern Montana, USA usually move actively among several widely spaced, mature, site‐faithful males in a mate search process that identifies vigorous mates. Typically, at least 90% of females practice this active sampling each year; each of the remaining females moves, before the rut begins, to a peripheral, isolated location with a single male and mates there without sampling. In 2001 and 2002, 90 and 100% of females, respectively, used the sampling strategy. The summer of 2003 was unusually hot and dry in western Montana. By September, when the pronghorn rut occurs, many pronghorn females were in visibly poor condition. In the winter that followed, 38% of females and 79% of males died, and in the following spring, only 17% of the surviving females gave birth. In the rut of 2003, 19% of females practiced the active sampling strategy. In 2004, 68% of females attempted to sample, even though there were only three mature males in the population. Among females that sampled, the number of switches away from harems and the number of males visited did not vary across years, except in 2004. The proportion of samplers in 2003 that died over winter was not different from the proportion of non‐samplers that died over winter, and among the survivors, the proportion of samplers that completed gestation was not different from the proportion of non‐samplers that completed gestation. The data suggest that pronghorn females have a strong motivation to sample potential mates, that sampling is abandoned when energy stores are low, and that yearly variation in the percent of females that sample is explained by variation in female condition.     

Sex‐specific food provisioning in a monomorphic seabird,the common guillemot Uria aalge: nest defence,foraging efficiency or parental effort?

Sexual differences in food provisioning rates of monomorphic seabirds are well known but poorly understood. Here, we address three hypotheses that attempt to explain female-biased food provisioning in common guillemots Uria aalge : (1) males spend more time in nest defence, (2) females have greater foraging efficiency, and (3) males allocate a greater proportion of foraging effort to self-maintenance. We found that males spent no more time with chicks than females but made longer trips and travelled further from the colony. There was extensive overlap between sexes in core foraging areas, indicating that females were not excluding males from feeding opportunities close to the colony. However, as a result of their longer trips, the total foraging areas of males were much greater than those of females. There was no difference between sexes in overall dive rate per hour at sea, in behaviour during individual dives or in a number of other measures of foraging efficiency including the frequency, depth and duration of dives and the dive: pause ratio during the final dive bout of each trip, which was presumably used by both sexes to obtain prey for the chick. These data strongly suggest that sexes did not differ in their ability to locate and capture prey. Yet males made almost twice as many dives per trip as females, suggesting that males made more dives than females for their own benefit. These results support the hypothesis that female-biased food provisioning arose from a difference between sexes in the allocation of foraging effort between parents and offspring, in anticipation of a prolonged period of male-only post-fledging care of the chick, and not from differences in foraging efficiency or time spent in nest defence.