Facilitation of parental behavior in ring doves by systemic or intracranial injections of prolactin

Systemic administration of ovine prolactin (PRL) has been previously reported to stimulate parental feeding behavior toward 7-day-old foster squabs by nonbreeding ring doves with previous breeding experience. The first of the present experiments reexamined this claim in experienced, nonbreeding birds given test squabs of different ages. Each visually isolated male and female dove was given twice-daily subcutaneous injections of ovine PRL or vehicle for 7 days and then tested for parental responses toward a single 1-3, 6-8, or 11- to 13-day-old foster squab. Prolactin significantly increased the incidence or frequency of parental regurgitation-feeding episodes in tests with all three squab age groups and, in addition, increased the incidence of parental feeding invitations (squab-oriented bill openings) in tests with 6- to 8-day-old squabs. A second study explored the degree to which PRL can act directly on the central nervous system to facilitate parental activity in the absence of peripheral cues generated from PRL-induced changes in other target organs, such as those associated with crop sac growth and distension. In this experiment, 6- to 8-day-old test squabs were used to determine if parental behavior is enhanced by twice-daily intracerebroventricular (ICV) injections of PRL in doses below those required to stimulate peripheral target organs. Injection schedules and behavior testing procedures were the same as those used in Experiment 1. However, half of the ICV PRL-treated and ICV vehicle-treated birds were food deprived for 16 hr before and during the test in order to control for PRL-induced hyperphagia and resulting crop sac distension, which could confound the results by generating peripheral stimuli conductive to the display of regurgitation-feeding behavior. Intracranial injections of prolactin significantly increased the incidence of feeding behavior, parental feeding invitations, and crouching or sitting in the nest in food-deprived doves but not in freely fed animals. Empty crop sac weights of freely fed and food-deprived PRL-treated birds were not increased above control values, thus indicating that ICV PRL treatment did not result in significant stimulation of peripheral target organs. These results demonstrate a facilitative action of PRL on regurgitation-feeding responses and associated parental behaviors that is not restricted to squabs of one particular age range. They also indicate that PRL is capable of acting directly on the brain to promote these activities in the absence of PRL-induced changes in the crop sac and other peripheral target organs.     

The Roles of Stimuli from Young, Previous Breeding Experience, and Prolactin in Regulating Parental Behavior in Ring Doves (Streptopelia risoria)

In addition to stimulating crop "milk" formation in ring doves, prolactin (PRL) may promote the parental regurgitation behavior that transfers this "milk" to the young at the time of hatching. Although earlier studies suggest that previous breeding experience is an important modulator of PRL-induced parental regurgitation behavior in ring doves, the ways in which experience, hormones, and stimuli from young interact to promote parental behavior have not been well characterized in this species. In the first study, untreated, nonbreeding female doves with and without previous breeding experience were given 10 daily parental behavior tests (2 h/day) with a hungry 5- to 10-day-old foster squab. Experienced females exhibited a higher incidence of regurgitation behavior, defensive behavior, and crouching or sitting in the nest than did inexperienced females. In a second study, nonbreeding females were given 10 daily tests for parental behavior while they received sc injections of ovine PRL or vehicle. Prolactin reduced squab-directed aggression and increased the incidence of regurgitation feeding behavior of foster squabs in both experienced and inexperienced females. However, the average number of regurgitation feeding acts displayed by those PRL-treated females that showed the behavior was over eight times higher in experienced females than in inexperienced females. Previous experience also enhanced the stimulatory effects of PRL on defensive behavior and crouching or sitting in the nest. The parental behavior exhibited by nonbreeding, PRL-treated experienced females was qualitatively and quantitatively similar to that observed in normally breeding females during a single test with their own hungry 5- to 10-day-old squabs. These findings indicate that PRL and previous breeding experience both enhance the parental responsiveness of nonbreeding female doves and that under optimal hormonal, experiential, and squab exposure conditions, nonbreeding doves exhibit levels of parental activity that rival those of normally breeding parents.     

Olfaction and parental behavior in ring dove

In the ring dove, several sensory cues emanating from the squab (young) have been shown to be important in maintaining parental care. However, no information exists on the role of olfaction in parental behavior. In the experiments described, the body odor of squabs was artificially altered by application of a fruit-scented substance to its back. This resulted in high mortality of treated squabs by day 7 post-hatching. The body weights of the fruit-scented squabs that died were lower than those of living controls, suggesting that some change in parental feeding had occurred. Behavioral observations also indicated qualitative differences in parental care towards fruit-scented vs control young. Toxicity was ruled out as a cause of squab death since subcutaneous injection of the fruit substance to squabs led to 100% squab survival. High squab mortality following fruit-scent treatment could be prevented by bilateral olfactory nerve cuts in the parents. Taken together, these data suggest that olfactory cues may play a role in parental care in ring doves, and add support to the notion that olfactory cues can influence avian behavior.     

Effect of parental feeding activity on squab-induced crop sac growth in ring doves (Streptopelia risoria)

Effects of parental regurgitation feeding activity on crop sac development were studied in mate-separated male and female ring doves given 2 hr of daily exposure to food-deprived or recently fed squabs, for 4 consecutive days during the early posthatching period of the breeding cycle. In both sexes, food-deprived squabs stimulated more squab-directed activity, more parental regurgitation feeding activity, and greater crop sac development than recently fed young. Crop sac weights of males in both groups tended to be positively correlated with one or more parental activities. Correlations obtained in males exposed to food-deprived young further suggested that tactile stimuli associated with regurgitation behavior may promote crop sac development. In contrast to males, crop sac weights of females in both groups were not highly correlated with any type of contact-related parental activity or group of activities. These results, together with previous findings, suggest that nontactile stimuli from young played some role in mediating female crop sac weight differences in the two exposure conditions.     

Brood Size Affects Behavior, Interclutch Interval, LH Levels, and Weight in Ring Dove (Streptopelia risoria) Breeding Pairs

This study examines the effects of experimental manipulation of brood size (one or two squabs) on the behavior, interclutch interval, plasma LH concentrations, and weights of ring dove parents. Twelve dove pairs were observed, sampled, and weighed over a cycle with one and a cycle with two squabs. Before hatch, no parameter showed any difference between pairs which would subsequently have one or have two squabs. After hatch, males and females having one squab fed less, while males showed more perch-, bow-, and nest-cooing over the 2 weeks after hatch. Females also showed more nest-cooing with one squab and a shorter interclutch interval. For both sexes the plasma LH concentrations were higher when rearing a single squab, showed a lesser decrease after hatch, and increased more rapidly. Both sexes also showed a smaller weight loss when rearing a single squab. The results show that the intricate relationships between behavior, physiology, and reproduction in the ring dove are tuned to brood size and emphasize the latter factor as an important and meaningful variable in the doves' reproductive cycle.     

L-carnitine supplementation in breeding pigeons: impact on zootechnical performance and carnitine metabolism

In the first experiment (Exp1), three consecutive breeding rounds were performed by two groups of six pigeon couples in order to study the impact of L-carnitine supplementation (80 mg x d(-1)) of parent pigeons on zootechnical performance. Both in the second and third experiments (Exp2, Exp3), one breeding round was performed by two groups of six pigeon couples to reveal the biochemical background of the increase in squab growth, the limitation of body weight decrease in male parent birds and the tendency for an improved cumulative feed efficiency due to L-carnitine supplementation in Exp1. Growth improvement of the squabs with L-carnitine was only seen when the parent pigeons were supplemented, together with a marked rise in the body weight of the parent birds around hatching. Based on the results of the crop milk analysis, growth improvement was probably due to a quantitative impact on crop milk production. The crop milk from the supplemented groups in both Exp2 and Exp3 had increased levels of carnitine. Carnitine, gamma-butyrobetaine and acetylcarnitine were increased in plasma samples of the supplemented parent pigeons. No differences were present in the squabs' plasma for these parameters. In the squabs of Exp3, no changes were seen in the proportional growth or the protein content of the heart, breast muscle and liver, but the breast muscle of the squabs from the supplemented group in Exp3 showed a considerable rise in carnitine and a marked decrease in gamma-butyrobetaine.     

Parental versus offspring control on food division within the brood: the role of hatching asynchrony

Using an individual-based simulation model we study how different mechanisms of food division among multiple offspring influence nestling number and quality, as well as parental effort. We consider the combination of different scenarios of food availability (feeding conditions), hatching asynchrony and food division. If parents have full control on how to divide food among offspring, asynchronous broods have higher breeding performance than synchronous ones in a wide range of feeding conditions, giving theoretical support to empirically proved benefits of hatching asynchrony. If parents accept the outcome of sibling competition there is a threshold in feeding conditions below which asynchronous broods produced more fledglings and the reverse was true above the threshold. Interestingly, parents relying on the outcome of nestling competition do not necessarily differ in breeding performance from those which have full control over food allocation. Our study combines hatching asynchrony, provisioning behaviour of parents, jostling behaviour of nestlings and feeding conditions as a network of interacting processes of enormous interest to fully understand the parent–offspring conflict.     

Food availability and the male's role in parental care in double-brooded Treecreepers Certhia familiaris

The aim of this work was to examine differences in paternal and maternal care in a double-brooded, monogamous species, the Treecreeper Certhia familiaris, in relation to food availability. As a measure of parental care, we recorded the hourly feeding activity of parents when the nestlings from their first and second breeding attempts were 7 and 12 days old. Feeding frequency of the first brood increased with the age of the nestlings and also with the brood size when 12 days old. While the feeding activities of the females were similar with respect to the first and second broods, the males were less active and failed to provide any food to their nestlings in 15 cases out of 28 second broods. In spite of this, the fledglings from the second broods were heavier than those in the first. Such a pattern of male behaviour was possible without being a disadvantage to the chicks because the food supply increased during the breeding season and the female could provide food for the young alone. Thus paternal care was particularly important in times of poor food supply, i.e. during the first brood, where the extent of these males' activity in feeding the 7-day-old nestlings was positively correlated with the average mass of the nestlings. Our results support the idea that the male of monogamous, altricial bird species often makes important contributions to raising the young, especially during periods when it is difficult for the female to do so alone. Males show flexibility in their pattern of parental care, and male Treecreepers change their contribution to the first and second broods within the same season.     

Hatching Asynchrony Decreases the Magnitude of Parental Care in Domesticated Zebra Finches: Empirical Support for the Peak Load Reduction Hypothesis

Parent–offspring conflict over the supply of parental care results in offspring attempting to exert control using begging behaviours and parents attempting to exert control by manipulating brood sizes and hatching patterns. The peak load reduction hypothesis proposes that parents can exert control via hatching asynchrony, as the level of competition amongst siblings is determined by their age differences and not by their growth rates. Theoretically, this benefits the parents by reducing both the peak load of the offspring's demand and their overall demand for food and benefits the offspring by reducing the amplification of their competition. However, the peak load reduction hypothesis has only received mixed support. Here, we describe an experiment where we manipulated the hatching patterns of domesticated zebra finch Taeniopygia guttata broods and quantified patterns of nestling begging and parental feeding effort. There was no difference in the begging intensity of nestlings raised in asynchronous or experimentally synchronous broods, yet parental feeding effort was lower when provisioning asynchronous broods and particularly so when levels of nestling begging were low. Further, both parents acted in unison, as there was no evidence of parentally biased favouritism in relation to hatching pattern. Therefore, our study provided empirical support for the prediction that hatching asynchrony reduces the feeding effort of parents, thereby providing empirical support for the peak load reduction hypothesis.     

FACTORS AFFECTING EGG-WEIGHT, BODY-WEIGHT AND MOULT OF THE WOODPIGEON COLUMBA PALUMBUS

The heaviest clutches (2 eggs) laid by Woodpigeons Columba palumbus in a Cambridgeshire study area weighed 30% more than the lightest. Yet the variation in egg-weight within clutches was less than 1 %. Irrespective of initial weight, eggs lost weight at the same constant rate during incubation. Heavy eggs hatched more successfully than light eggs and none weighing less than 16 g hatched. There was no correlation between chicks' weight at hatching and their weight at day 6 during the July-September part of the breeding season. The ability to feed crop milk at this stage could compensate for low chick-weight, but this might not be true early in the season. Weight at day 6 was correlated with the weight at day 16 or 17. The growth pattern is discussed. Chicks in broods of one achieved a higher weight at day 17 than those in broods of two. The survival rate both in and after leaving the nest was the same in both brood-sizes. Chick-weight in artificially created broods of three was almost as high as in broods of two, but again data refer to the July-September period when abundant cereal food is available. Survival before and after fledging was lower in broods of three. Clutch- and egg-weight declined from April until September. It is suggested that this is adaptive, in that the adults produce heavier eggs when food supplies are most difficult to collect. The critical period probably occurs during the few days when the adult must produce crop milk and the young cannot be left unattended. Thus egg-weight depends on the female's capacity to acquire nutrients, and is related to the needs of embryonic development and the amount of compensation in nutrient supply which can be provided immediately after hatching. But clutch-size is more related to the bird's ability to feed and rear young to the point of fledging, thereby influencing the number of offspring which survive to leave progeny. Egg-weight and female body-weight were positively correlated in females weighing less than 480 g but not in heavier females. First-year birds did not acquire adult weight until midsummer and they would probably produce light eggs if they could breed before this month. However, their gonads do not recrudesce until July and this prevents them breeding in the spring. Seasonal changes in body-weight and fat content of adults and first-year birds are described and discussed; differences were noted between adult males and females which were considered to be adaptive. The moult is described. It begins in April and continues until November, approximately one pair of primaries being replaced per month. The moult ceases during the winter months, when it is known that food supplies become limiting. Woodpigeons lay light eggs relative to their body-weight but can achieve the extra parental care needed for the altricial chicks by producing crop milk. Because the moult is extended, the energy demands of moulting and breeding combined are relatively low and this enables the Woodpigeon to have a long breeding season and to moult coincidentally.     

Shared or Unshared Parental Care in Overwintering Brent Geese (Branta bernicla hrota)

We examine brood size effects on the behaviour of wintering parent and juvenile brent geese (Branta bernicla hrota) to test predictions of shared and unshared parental care models. The behaviour of both parents and offspring appear to be influenced by declining food availability over the winter. Parental vigilance increased with brood size and may be explained by vigilance having functions in addition to antipredator behaviour where the benefits are shared among the brood. There was no increase in parental aggression with brood size and this does not fit the prediction of shared care. Nevertheless, large families are able to monopolize better feeding areas compared with smaller families and large families static feed more but walk feed less than do small families, the former apparently being the preferred mode. The presence of additional young, rather than increasing the amount of parental aggression, seems to enhance the family's competitive ability. Because parents with large broods benefit from enhanced access to resources there is likely to be no additional significant cost in the parental care of larger broods (sensu Trivers 1972 ).     

鸽乳的生物学功能及其生成调控

鸽(Columba livia)是少数几种能分泌营养液哺育雏鸟的鸟类之一。孵化期的亲鸽嗉囊壁逐渐增厚,当雏鸽被孵出,亲鸽嗉囊会产生鸽乳(crop milk)以哺育雏鸽。鸽乳的营养成分及其生物学功能与哺乳动物的乳汁相似,其产生过程受催乳素的调节。在催乳素作用下,嗉囊上皮细胞快速增殖脱落形成鸽乳,该过程可能与膜联蛋白Icp35(AnxIcp35)等关键基因的转录以及JAK/STAT和Wnt等信号通路的激活有关。本文对鸽乳的主要成分、生物学功能和泌乳过程中嗉囊组织学变化进行了介绍,对鸽乳生成过程中特异的基因变化和分子调控机制进行了总结,以期为后续的相关研究工作提供有益的参考。     

Complex patterns of food allocation in asynchronously hatching broods of crimson rosellas

In birds, asynchronous hatching typically leads to lower growth and survival of last-hatched chicks. However, all crimson rosella Platycercus elegans, chicks grow at the same rate, although first-hatched chicks can be as much as seven times heavier than last-hatched chicks at the end of hatching. We examined the delivery and distribution of food to 18 rosella broods by videotaping feeds and simultaneously recording mass changes in the nestbox using a digital balance. Parents visited the nest infrequently and delivered loads of up to 25% of their body weight during a feeding visit. Male rosellas consistently delivered larger loads and consequently had higher feeding rates (g/h) than females. Parents distributed food between chicks by direct regurgitation in a series of up to 51 food transfers. Overall, chicks of all hatching ranks received equal numbers of transfers, but parents differed in how they distributed food within the brood. Males fed first-hatched chicks more than last-hatched chicks, whereas females distributed food equally to all chicks. Selective feeding of small chicks might be costly to females since they delivered food more slowly than males and spent more time in the nestbox. Thus female rosellas may invest more in current reproduction than males. Parents also distributed food differently to male and female chicks. Large males were fed more than all other nestlings, while female nestlings were fed equally irrespective of size. This study confirms that complex patterns of parental allocation occur in wild populations. Copyright 1999 The Association for the Study of Animal Behaviour.     

The effects of food abundance on breeding performance and adult time budgets of Guillemots Uria aalge

The breeding performance, food fed to chicks and adult time budgets of Guillemots Uria aalge were examined in a year of high and a year of low food availabiIity. There was no difference between the 2 years in reproductive success, although the rate of chick feeding, chick weight and fledging success were greater in the year of high food availability. On average, chick prey items were larger in the poor food year, but this was insufficient to compensate for the lower feeding frequency. Chick feeding frequency did not differ between days in the good year but did increase later in the season in the poor food year. Compared with the high food availability year, adult Guillemots in the year of low food availability spent much less time resting at the breeding colony. and their foraging trips were twice as long. Foraging birds tended to make several successive trips before resuming brooding duties from their mates when food supplies were good, but in the low food availability year single trips were the norm. These results demonstrate that predators experiencing reduced food supply may mitigate the effects on their reproductive output by shifting their time allocation such that more time is available for foraging.     

Harsh nutritional environment has positive and negative consequences for family living in a burying beetle

Harsh environmental conditions in form of low food availability for both offspring and parents alike can affect breeding behavior and success. There has been evidence that food scarce environments can induce competition between family members, and this might be intensified when parents are caring as a pair and not alone. On the other hand, it is possible that a harsh, food-poor environment could also promote cooperative behaviors within a family, leading, for example, to a higher breeding success of pairs than of single parents. We studied the influence of a harsh nutritional environment on the fitness outcome of family living in the burying beetle Nicrophorus vespilloides. These beetles use vertebrate carcasses for reproduction. We manipulated food availability on two levels: before and during breeding. We then compared the effect of these manipulations in broods with either single females or biparentally breeding males and females. We show that pairs of beetles that experienced a food-poor environment before breeding consumed a higher quantity of the carcass than well-fed pairs or single females. Nevertheless, they were more successful in raising a brood with higher larval survival compared to pairs that did not experience a food shortage before breeding. We also show that food availability during breeding and social condition had independent effects on the mass of the broods raised, with lighter broods in biparental families than in uniparental ones and on smaller carcasses. Our study thus indicates that a harsh nutritional environment can increase both cooperative as well as competitive interactions between family members. Moreover, our results suggest that it can either hamper or drive the formation of a family because parents choose to restrain reproductive investment in a current brood or are encouraged to breed in a food-poor environment, depending on former experiences and their own nutritional status.     

Supplementary feeding increases Common Buzzard Buteo buteo productivity but only in poor‐quality habitat

Temporal heterogeneity in the effects of food supply during the breeding season on the productivity of the Common Buzzard Buteo buteo was investigated in a supplementary feeding experiment. Pairs were fed artificially (1) before egg‐laying, (2) after chicks hatched and (3) continuously throughout the season, and compared with (4) unfed controls. Pairs fed before egg‐laying had marginally larger clutches than those not fed, but lay date, egg volume and weight, brood size and hatching success were unaffected. Territorial quality had far greater effects, with pairs nesting in low‐quality habitats (bog, scrub and semi‐natural grassland) laying later and having lower hatching success, smaller broods and fewer fledglings than those in more productive agricultural landscapes. Supplementary feeding after egg hatching neutralized the negative effect of poor habitat, resulting in fed birds having significantly more fledglings. This study emphasizes the importance of food availability when provisioning chicks in suboptimal habitats and has implications for the success of diversionary feeding in reducing game losses to Buzzards.     

Ural owl sex allocation and parental investment under poor food conditions

Parents are expected to overproduce the less costly sex under poor food conditions. The previously regular 3-year cycle in the abundance of voles, the main prey of the Ural owl, Strix uralensis, temporarily disappeared in 1999–2001. We studied Ural owls' parental feeding investment and sex allocation during these poor-quality years. We sexed hatchlings and embryos in unhatched eggs of all 131 broods produced during these years. Population wide, the owls produced significantly more males (56%). The parental food investment in the brood was estimated by sorting out the prey remains in the bottom of nest boxes. Food delivered to 83 broods without chick mortality showed no clear sex-specific investment. Nestling mortality was equal in both sexes. Thus, evidence for an investment-driven sex allocation is weak. Neither laying date, brood size nor the female's condition correlated with offspring sex ratios. In these poor years, parents provided less food per chick and the fledging weight of daughters was reduced more than the weight of sons compared with years of high food abundance (1983 and 1986). We discuss, in relation to published studies, the possibility of a sex-allocation scenario where, under poor food conditions, a daughter's long-term fitness is reduced more than a son's.     

Temporal changes in food resources,parental feeding and breeding success of Heron Island silvereyes,Zosterops lateralis chlorocephala

The influences of the temporal change in food supply on the parental feeding effort and breeding success of silvereyes,Zosterops lateralis chlorocephala, was investigated on Heron Island, Australia. Food supply (arthropods and figs) declined as the breeding season progressed. The parental feeding rate and growth of nestlings were lower when food supply was poor. When available, dominant pairs fed their young more figs and fewer arthropods than lower ranking pairs. Dominant pairs raised heavier young than lower ranking pairs when food supply was poor, while there were no significant differences between them when food supply was rich. When food supply was rich, pairs delivering greater amounts of arthropods reared nestlings better, whereas feeding more figs did not improve growth of nestlings. When food supply was poor, pairs spending a longer time at the nest reared nestlings better.     

Chick parasitism by blowflies affects feeding rates in a Mediterranean population of blue tits

Offspring fitness depends on interactions between parental care and environmental constraints. It has been suggested that in altricial birds parents are able to compensate for the detrimental effects of ectoparasites by improving food provisioning. We tested this prediction in a population of blue tits highly parasitized by blowfly larvae. The frequency of parental feeding visits was significantly higher in parasitized broods than in broods experimentally deparasitized. Despite a strong increase in parental care, chicks of parasitized broods were lighter, smaller, and more anaemic than chicks in deparasitized broods. Parents invest more in feeding parasitized young but cannot fully compensate for the negative effects of parasites, hence young are in poor condition at fledging.     

Shared parental care is costly for nestlings of common cuckoos and their great reed warbler hosts

Obligate avian brood parasitism typically involves one of 2strategies: parasite chicks are either 1) virulent and evictall other eggs and nest mates to be raised alone or 2) moretolerant and share foster parental care with host chicks forsome or the entirety of the nestling period. We studied theconsequences of experimentally forced mixed broods of age-matchedone common cuckoo (Cuculus canorus) and 2 great reed warbler(Acrocephalus arundinaceus) chicks. In these broods, both cuckooand host chicks grew slower than did either individual cuckoosor great reed warblers in broods of 1 parasite or 3 host chicks,respectively. Video records showed that in mixed broods, cuckoochicks received feedings less frequently than the 33% predictedby chance at 4 days of age but parental food allocations increasedto chance levels at 8 days of age. The consistent patterns oflower growth rates arose even though chicks in broods of 1 parasiteand 2 hosts received the largest prey items per feeding. Inaddition, several other measures of parental provisioning alsodid not predict species and brood-specific differences in nestlinggrowth rates across the different treatments. However, variationin begging displays and its specific costs on host and parasitechicks in the different nest treatments were not quantifiedin this study. We conclude that young of nest mate–evictorcommon cuckoos benefit from the sole occupancy of host nestsin part owing to an initial competitive disadvantage for parentalcare in broods with age-matched great reed warbler chicks.