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.     

FOOD RESOURCES, TERRITORY DENSITY AND REPRODUCTIVE SUCCESS OF AN ISLAND SILVEREYE POPULATION ZOSTEROPS LATERALIS

We examined the relationships between food resources, territory density and some breeding parameters (individual reproductive success and parental age) of a Capricorn Silvereye population during two years' detailed study on Heron Island, Great Barrier Reef. The territorial behaviour of the Silvereyes included dawn song. aggression and distinctive vocalizations. During both years, about 85% of pairs occupied territories although the population sizes differed. The dispersion pattern of territories was not regular and was correlated with the density of figs and human food scraps. Nestlings were fed more figs as they grew, and the parents foraged in fig trees outside their territories. However, only about 60%, of territorial pairs fledged young. Pairs which fledged most young were older, fed more insects to their nestlings, and nested in areas containing more fruiting fig trees per territory. We conclude that food resources were in short supply, and that access to fig trees provided breeding birds with a quick energy source while they searched for insect protein for the young. The data are consistent with the predictions of the ‘sufficient resource‘ hypothesis of the adaptive significance of territoriality but not with its assumption that the principal benefit is the food within the territory.     

THE PRESENT AND PAST DISTRIBUTION OF THE BALD IBIS IN THE PROVINCE OF THE CAPE OF GOOD HOPE

Tarboton, W. R. 1981. Cooperative breeding and group territoriality in the Black Tit. Ostrich 52:216-225.

In a small, colour-ringed population of Black Tits Parus niger in central Transvaal, 11 of 19 observed breeding units comprised pairs with one to three helper-males. These pairs and groups defended permanent territories, the size of which correlated with the size of the group. There were significantly more territorial disputes during winter when less food was available than in summer. Breeding occurred in summer and the female alone built the nest, incubated the eggs and brooded the young while they were small. During this time she was fed by the alpha male and helper males, although before egg-laying the alpha male prevented helpers from courtship-feeding her. On average, unassisted pairs reared 0,88 young/season whereas pairs with helpers reared 1,55 young/season. However the feeding rate of nestlings of pairs with helpers was not higher than that of unassisted pairs and the number of young reared per group did not correlate with the number of helpers within the group.

The helper system in Black Tits was associated with a skewed sex-ratio (1,7:1 males: females) in the adult population and the data are consistent with the “hopeful reproductive” hypothesis for cooperative breeding.     

Relative performance of hybrid nestlings in Ficedula flycatchers: a translocation experiment

Ecological speciation predicts that hybrids should experience relatively low fitness in the local environments of their parental species. In this study, we performed a translocation experiment of nestling hybrids between collared and pied flycatchers into the nests of conspecific pairs of their parental species. Our aim was to compare the performance of hybrids with purebred nestlings. Nestling collared flycatchers are known to beg and grow faster than nestling pied flycatchers under favorable conditions, but to experience higher mortality than nestling pied flycatchers under food limitation. The experiment was performed relatively late in the breeding season when food is limited. If hybrid nestlings have an intermediate growth potential and begging intensity, we expected them to beg and grow faster, but also to experience lower survival than pied flycatchers. In comparison with nestling collared flycatchers, we expected them to beg and grow slower, but to survive better. We found that nestling collared flycatchers indeed begged significantly faster and experienced higher mortality than nestling hybrids. Moreover, nestling hybrids had higher weight and tended to beg faster than nestling pied flycatchers, but we did not detect a difference in survival between the latter two groups of nestlings. We conclude that hybrid Ficedula nestlings appear to have a better intrinsic adaptation to food limitation late in the breeding season compared with nestling collared flycatchers. We discuss possible implications for gene flow between the two species.     

Azure‐winged Magpies Cyanopica cyanus trade off reproductive success and parental care by establishing a size hierarchy among nestlings

It is common in birds that the sizes of nestlings vary greatly when multiple young are produced in one nest. However, the methods used by parents to establish size hierarchy among nestlings and their effect on parental provisioning pattern may differ between species. In the Azure‐winged Magpie Cyanopica cyanus, we explored how and why parents controlled the sizes of nestlings. Asynchronous hatching was the main cause of size hierarchy within the brood, although the laying of larger eggs later in the laying sequence reduced this effect. Parents with asynchronous broods produced more eggs and fledged more nestlings than those with synchronous broods but their brood provisioning rates, food delivery per feeding bout and feeding efficiency did not differ. We performed a cross‐fostering experiment to synchronize some asynchronous broods. Provisioning rates of asynchronous broods were lower than those of synchronized broods, but the daily growth rates and fledging body mass of their nestlings were not different. Our findings indicate that parents of asynchronous broods can achieve higher reproductive success than those of synchronous broods based on the same parental care, and the same reproductive success as those of synchronized broods based on less parental care. It appears that parent birds can better trade off reproductive success and parental care by establishing a size hierarchy among nestlings.     

SOME NOTES ON THE SPOTTED FOREST THRUSH

Brown, C. J., Riekert, B. R. &; Morsbach R. J. 1987. The breeding biology of the African Scops owl. Ostrich 58: 58–64.

The incubation and nestling periods of two pairs of African Scops Owls Otus senegalensis breeding in nesting boxes in the Daan Viljoen Game Park near Windhoek were studied. The incubation and nesting periods were about 22 ± 2 days and 25–28 days respectively. Incubation and brooding was by the female. The male provided all the food during the incubation period, but by the end of the nestling period 30% of food was brought by the female. The growth of the nestlings, parental behaviour and foraging methods are describe2 Of 100 food items brought to the nests, 93% (by number) consisted of arthropods, 6% reptiles and 1% small mammals.     

Acorns,insects, and the diet of adult versus nestling Acorn Woodpeckers

ABSTRACT The diet of Acorn Woodpeckers (Melanerpes formicivorus) in central coastal California consists of a mixture of high‐quality (insects) and low‐quality (stored acorns) food during the spring breeding season. We used stable isotope ratios obtained from blood samples to estimate possible differences in the proportion of these items being fed to nestlings and being consumed by breeding adults, as well as the extent to which the diet of nestlings shifts between insects and acorns during the nestling period. Based on both feeding observations and items recovered from nestlings, older nestlings were fed 28% acorns. Using this value as a baseline for the isotope analyses, the diet of breeding adults was estimated to consist of 90% acorns. Based on repeated samples from the same nestlings over time, the estimated proportion of acorns in their diet increased from 19% in 9‐ to 12‐d‐old nestlings to 42% in 23‐ to 26‐d‐old nestlings. There was a significant correlation between the isotope values of adults and the nestlings they fed, indicating that different groups of Acorn Woodpeckers have significantly different diets. Although important for successful reproduction in this species, stored acorns are not the primary food resource used to feed young. Instead, the availability of stored acorns allows adult Acorn Woodpeckers to provide nestlings with more protein‐rich insects while maintaining themselves on relatively protein‐poor, low‐quality acorns. Differences in the diets of adults and their nestlings are likely widespread among species that feed, at least in part, on low‐quality foods, such as fruit and seeds, during the breeding season.     

Male parental care promotes early fledging in an open-nester, the Willow Warbler Phylloscopus trochilus

The importance of male parental care to female reproductive success was investigated in the monogamous Willow Warbler Phylloscopus trochilus by removing the male parent at two different stages of the breeding cycle. Females that were widowed at the start of egg-laying continued breeding and managed to raise their brood on their own with no apparent reductions in numbers fledged or fledgling body-mass. The widowed females compensated for the loss of male assistance by increasing their own food provisioning rate as compared with control females. However, widows spent less time brooding the small young, and the growth rate of nestlings was reduced. In nests where the male parent was removed 7 days after the eggs hatched, the subsequent growth rate of nestlings was still affected, which suggests that male care is influential throughout the nestling period. On average, broods reared by widows fledged 2 days later than did broods of control females. An extension of the nestling period may appreciably affect reproductive success, since 68% of nests failed due to predation, mostly during the nestling period. We suggest that the main role of male parental care in the Willow Warbler is to assure a high growth rate of nestlings, which leads to early fledging and hence a reduced risk of nest predation.     

Seasonal variation in food availability influences the breeding strategy of White‐collared Blackbirds Turdus albocinctus on the Tibetan Plateau

Parent birds show a continuous spectrum of breeding strategies, ranging from a low‐fecundity and high‐survival pattern to a high‐fecundity, low‐survival pattern. Investigations of parental breeding strategies under variable environmental conditions can illustrate how parents trade‐off the benefits and costs of these two extreme strategies. White‐collared Blackbirds Turdus albocinctus can breed twice a year on the Tibetan Plateau. We show that both life‐history traits and parental feeding behaviour differ between these two breeding attempts. In the first attempt, the birds produced small clutches and fledged a small number of nestlings of high body condition. In the second attempt, they produced larger clutches and fledged more nestlings of lower body condition. Males made greater contributions to brood provisioning compared with females in the first attempt but there was no sex difference in brood provisioning in the second attempt. In the first attempt, producing smaller clutches can shorten the nestling period, and the increased male contribution to brood provisioning can protect the energy reserves of females. Thus, females can begin a second attempt sooner and produce larger clutches. During the second nesting attempt, when conditions are warmer and wetter, parents rely on a broader array of food types (both invertebrates and plant material, primarily berries) than during the first attempt, which includes only animal food such as arthropods and annelids. We suggest that this difference in breeding strategies between nesting attempts and sexes is in part influenced by marked seasonal variation in food availability.     

Parental Self-Feeding Effects on Parental Care Levels and Time Allocation in Palestine Sunbirds

The trade-off between parents feeding themselves and their young is an important life history problem that can be considered in terms of optimal behavioral strategies. Recent studies on birds have tested how parents allocate the food between themselves and their young. Until now the effect of food consumption by parent birds on their food delivery to their young as well as other parental activities has rarely been studied. I have previously shown that parent Palestine sunbirds (Nectarinia osea) will consume nectar and liquidized arthropods from artificial feeders. However, they will only feed their young with whole arthropods. This provided a unique opportunity to experimentally manipulate the food eaten by parents independent of that fed to their offspring. Here, I hypothesized that parents invest in their current young according to the quality of food that they themselves consume. Breeding pairs with two or three nestlings were provided with feeders containing water (control), sucrose solution (0.75 mol) or liquidized mealworms mixed with sucrose solution (0.75 mol). As food quality in feeders increased (from water up to liquidized mealworms mixed with sucrose solution): 1) Parents (especially females) increased their food delivery of whole arthropod prey to their young. 2) Only males increased their nest guarding effort. Nestling food intake and growth rate increased with increasing food quality of parents and decreasing brood size. These results imply that increasing the nutrient content of foods consumed by parent sunbirds allow them to increase the rate at which other foods are delivered to their young and to increase the time spent on other parental care activities.     

Body weight,energy metabolism,and time in the life of birds

The breeding of birds, both large and small, is affected by two specific factors: (1) hypometry of egg weight relative to female body weight and (2) seasonality of breeding, with the favorable period being limited and almost equal for birds of different body sizes. Dozens of published allometric formulas describing the dependence of energy parameters of eggs and nestlings at different growth stages and the energy cost of parental care on the body weight of parents, eggs, and nestlings, respectively, are reviewed. It is shown that birds, especially species with a large body weight, repeatedly change their metabolic parameters during ontogeny in order to shorten the period of breeding and growth. In most species, the energy costs of breeding in both sexes are approximately equal. Bringing food in the bill allows birds to supply nestlings with the amount of energy that is dozens of times greater than that expended for obtaining the food. In placental mammals, only females are involved in offspring development. Therefore, the growth rate of embryos and energy expenditures for milk feeding are limited by the metabolic potential of the mother. As a consequence, mammalian offspring grow ten times slower than bird nestlings, the body weights of females being equal.     

Comparison of digestive efficiency in the parasitic great spotted cuckoo and its magpie host nestlings

Altricial nestlings are under strong selection pressures to optimize digestive efficiency because this is one of the main factors affecting nestling growth and survival. Bird species vary in their ability to assimilate different nutrients and current theory predicts that nestlings should also be able to adjust their nutritional physiology to feeding frequency. Variation in parental provisioning to nestlings would select for flexibility in nestling digestive physiology, which would allow maximization of nutrient assimilation. In the present study, by making use of a brood parasite–host study system in which great spotted cuckoo nestlings (Clamator glandarius) are reared by magpie (Pica pica) host foster parents when sharing the nest with host nestlings, we tested several predictions of the adaptive digestive efficiency paradigm. A hand‐feeding experiment was employed in which we fed both great spotted cuckoo and magpie nestlings with exactly the same diet simulating one food abundance period and one food deprivation period. The results obtained show that cuckoo nestlings ingested more food, gained significantly more weight during the abundance period, and assimilated a higher proportion of the ingested food than magpie nestlings. These results demonstrate for the first time that cuckoo nestlings enjoy digestive adaptations that favour a rapid processing of the ingested food, thereby maximizing their intake rate but without decreasing digestive efficiency. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 280–289.     

Mate size and breeding success in a monogamous cichlid fish

Synopsis The patterns of mate size and parental care of a monogamous cichlid fish,Cichlasoma maculicauda, were studied in Gatun Lake, Panama. Males defend territories which serve as courtship and nest sites. Within a population most mates in pairs are of equal size rank. In each pair the male is larger than the female, probably because most mature males are larger than most mature females. Clutch size increases with female body size. Male size affects breeding success in two ways. First, larger males provide nest sites less susceptible to destructive wave action. Second, young of larger males grow faster than young of smaller males. Large males defeat small males in contests for position in feeding areas, and this may provide their young with better feeding conditions. In the laboratory young growth rates increase with food abundance, and at high levels of food surpass those observed in nature. Fast growth of young reduces their vulnerability to predators and should allow parents to breed more often. Young survival rates improve with the size of the parents, so that larger fish raise more offspring at each breeding attempt. These observations suggest why preference for large mates should occur.     

Influence of Forest Seasonality on Gibbon Food Choice in the Rain Forests of Barito Ulu,Central Kalimantan

We describe the diet of two hybrid gibbon groups (Hylobates mulleri x H. agilis) in relation to forest seasonality. We collected data over 12 mo in lowland dipterocarp forest in the Barito Ulu research area, Central Kalimantan, Indonesia. Although non-fig fruit was the main dietary item (52–64% of diet), gibbon diet was most strongly influenced by the availability of flowers. During periods when flowers were most abundant and the gibbons increased consumption of them, they also ate figs or young leaves more often. We suggest that although flowers are nutritionally rich sources of food, providing relatively high levels of protein compared to fruit, they are unlikely to satiate gibbon hunger and they seek dietary bulk from figs or young leaves, because they are easily obtained. Rainfall also influenced food choice, and non-fig fruit availability had a weak influence on fruit selection for one group. The group concentrated feeding on the fruit of a few species when fruit was most abundant and ate a greater diversity of species when fruit was scarce. Gibbon diet appeared not to be influenced by changes in availability of figs, young leaves and diversity of fruiting species.     

Differential Begging and Locomotory Behaviour by Early and Late Hatched Nestlings Affecting the Distribution of Food in Asynchronously Hatched Broods of Altricial Birds

Distribution of food to early and late hatched nestlings was studied in asynchronously hatched broods of the great tit Parus major, the blackbird Turdus merula, and the fieldfare T. pilaris. Food distribution is related to the locomotory and begging behaviour and positions in the nest of these nestlings. Late hatched (small) nestlings were found to beg more often per feed than bigger nestlings and move more towards favoured positions in the nest to counteract selective feeding of bigger young. The functional significance of these differences in the behaviour of early and late hatched nestlings are discussed. It is argued that they are adaptive by 1) ensuring that each nestling survives when food supplies are ample, and 2) by mediating an optimal brood reduction when food is insufficient to raise the entire brood. The roles of asynchronous hatching, and selective feeding which follows from differential behaviour of early and late hatched young are discussed in relation to food conditions during the breeding season.     

Experimentally induced clutch size enlargements affect reproductive success in the Pied Flycatcher

We performed a food provisioning experiment in a population of Pied Flycatchers Ficedula hypoleuca breeding at high altitude in central Spain to test if food availability before and during laying determines clutch size. Food was provided to one of two pairs with the same date of initiation of nest-building (15 dyads of subsequently reproducing pairs were thus created). Food provisioning began on the day of initiation of nest-building and ended on the day after the last egg was laid. Although laying date was unaffected by the experiment, clutch size in the experimental treatment was significantly larger. This result could indicate that food availability at laying (1) proximately constrained clutch size or (2) that females evaluated future conditions for incubating eggs and feeding nestlings based on food availability at laying. Reproductive success (proportion of eggs that resulted in fledged young) was significantly reduced in the experimental treatment. This effect suggest that supplemented females were tricked by the experiment into laying more eggs than the number of eggs they were able to incubate with success and the number of nestlings they were able to feed, a source of error in clutch size adjustment which could be common in non-experimental situations.     

Experimental evidence for the relationship between food supply, parental effort and chick survival in the Lesser Black-backed Gull Larus fuscus

We studied breeding success, chick growth, parental effort and chick behaviour in two groups of Lesser Black-backed Gulls Larus fuscus whose chicks were provided with additional food until 7 days after hatching or until fledging. These data were compared with those from control pairs which we studied simultaneously to test the hypotheses that food was in short supply during the chick stage at the colony site and that in such circumstances the behaviour of adults and young is mainly responsible for the low success. Pairs whose chicks were fed with additional food until fledging showed a higher fledging success than control pairs (intermediate for pairs of first experimental group). During the first week after hatching, experimental adults of both groups were present together at the territory for longer than control pairs. In adult females of experimental pairs, the length of feeding trips was shorter than in females of control pairs, whilst the rate of chick feeding was more frequent in the experimental broods. After the chicks were 7 days old, differences were significant only for the experimental pairs whose chicks were provided with additional food until fledging. Chicks fed until fledging showed a higher daily mass and wing-length increments and reached a higher fledging mass at an earlier age than both control chicks and chicks which were provided with additional food until day 7. Starvation occurred only in control chicks and in chicks of the first experimental group after we had stopped providing food. When food was in short supply, fledging success of gulls was adversely affected as a result of both starvation (because of the lower feeding rates of chicks) and a higher predation rate (arising from changes in behaviour of both adults and chicks).     

Horned larks on the Tibetan Plateau adjust the breeding strategy according to the seasonal changes in the risk of nest predation and food availability

Songbirds in seasonal environments often adjust their breeding strategy according to spatial or temporal changes in breeding conditions. Here we investigate how horned larks Eremophila alpestris, a multi‐brooded songbird on the Tibetan Plateau, responded to the changing risk of nest predation and food availability across breeding attempts. We showed that both nest concealment and food supply increased with plant growth, and horned larks adjusted their breeding strategies accordingly. First they selected nest‐sites where predator density was low, which enhanced nest survival. Second, clutch size increased with improving breeding conditions. They did not adopt an ‘egg‐size’ strategy as egg size did not change with laying sequence or breeding attempt. Instead, they adopted the ‘brood survival (feeding later‐hatched nestlings more)’ and ‘brood reduction (feeding early‐hatched nestlings more)’ strategies during early and later attempts. Moreover, nestlings’ growth varied with breeding attempt: more energy was invested into the growth of body mass during the first attempt but more energy was expended on the growth of linear structures during later attempts. This difference in energy allocation reflected changing food availability. We suggest that temporal changes of environmental factors are also the important force driving the evolution of avian breeding strategies.     

ENVIRONMENTAL INFLUENCES ON GROWTH AND SURVIVAL OF NESTLING HOUSE MARTINS DELICHON URBICA

Growth of nestling House Martins was studied in relation to (a) conditions in the external environment and (b) aspects of their breeding biology. The dependence of growth performance on (1) hatchling weights, (2) relative difference in hatchling weights within broods, (3) brood size,(4) season, (5) earliness of breeding in relation to other pairs in the colony, (6) timing of breeding in relation to the median breeding week of the colony and (7) aerial food abundance, was investigated by step-down multiple regression analysis. Up to the stage of the peak brood weight, early laying, small brood sizes and high hatchling weights were associated with higher nestling growth rates. Large relative differences in hatchling weights however tended to depress mean brood weights and increase weight differences (= size hierarchies) within broods. These differences in hatchling weights were considered to contribute significantly to 23% of all nestling deaths, because small, late hatching nestlings suffered very high mortality even when food was abundant. The nestlings which died showed a progressive reduction on growth rates and all succumbed before the 11th nestling day. Because these differences in hatchling weights can be linked to the food supply during laying rather than immediately prior to their death, it is considered that the mortality of these nestlings can ultimately be attributed to the low quality of eggs from which they hatched. There was a tendency for pre-hatching factors to diminish in importance throughout growth, while post-hatching factors increased in importance and, with one exception, were responsible for explaining all the significant variance in the growth characteristics of fledglings. The exception was that differences in wing-lengths in broods could be linked with weight differences at hatching. Food shortages lowered average brood weights prior to fledging. Because pairs breeding during the median breeding week had lighter young, it was inferred that competition for food during this peak of breeding activity had the effect of lowering nestling growth performance, although the overall effect was considered to be small. Early breeding pairs tended to have larger broods, and these large broods showed a lowered growth performance. However, early breeding pairs had relatively smaller weight and wing-length differences, in broods of a given size, than occurred in broods of late breeders. It was therefore concluded that early breeding pairs had some attribute which tended to minimize certain disadvantages of large broods. This effect appeared to be linked to the pair, rather than to season or food supply.     

杂色山雀双亲差异性育雏策略

社会性单配制鸟类的配偶双方在抚育子代时常存在性别差异,不同鸟种的雌雄双亲往往采取不同的育雏策略。以杂色山雀(Sittiparus varius)为研究对象,2017年3—7月对繁殖巢箱进行录像监测,记录杂色山雀育雏期亲代投入情况。分析结果显示:1)双亲递食率在育雏前期(4—6日龄)无显著差异,而育雏后期(10—12日龄)雌性的递食率显著高于雄性。2)雌性亲鸟后期递食率较育雏前期显著增加;而雄性亲鸟育雏前期和后期递食率无显著差异。3)雌性递食率与自身喙宽呈极显著正相关,雄性递食率与双亲体征参数均无相关关系。总的来说,在育雏阶段,杂色山雀雌性亲鸟的递食率随着雏鸟的需求和自身身体质量发生调整,雌性在育雏后期递食率显著升高,而雄性亲鸟递食率无变化,这可能与育雏期双亲投入分工不同有关。