Parental Feeding Rates Research Articles

Food availability and immune capacity in serin ( Serinus serinus ) nestlings

Parental feeding effort is an important determinant of chick development in birds. Quality and amount of food provided to each nestling, however, might affect the development of the immune system. Food availability around the nest site may account for part of the difference in body condition and immune capacity of nestlings. We tested this idea in the socially monogamous serin (Serinus serinus), investigating growth and immune capacity of nestlings in relation to food availability around the nest site. We used a set of immunological and serological assays, including antibody responses to sheep red blood cells (SRBCs), the T lymphocyte cell-mediated immune response (PHA), granulocyte:lymphocyte ratio (G:L), haematocrit and sedimentation rate. The results suggest that serins raised under poor environmental conditions were less immunocompetent. The immune response to PHA and SRBCs significantly increased with food availability. Haematocrit values were positively, sedimentation rate and the G:L ratio negatively correlated with food availability. Similar results were obtained when examining chick development in relation to the immunological and serological variables. However, there was a negative relationship between parental feeding rates and food availability, as well as between parental feeding rates and chick development. We conclude that body condition and immune capacity of nestlings are strongly correlated with the availability of food around the nest site.

Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows

Many studies fail to show relationships between ectoparasite loads and nestling growth rates. One explanation is that parent birds increase feeding rates to compensate for nestling energetic losses to ectoparasites. Nestling begging behaviours could signal need to parents. Accordingly, we tested whether higher flea and blow fly loads in tree swallow (Tachycineta bicolor) nests were associated with smaller nestlings, higher parental feeding rates, and increased nestling begging intensity. The study area was the Gaspereau Valley of Nova Scotia, Canada. When nestlings were 10 days old, parental feeding rates and nestling begging intensity were measured with tape recorders. At 13 days of age, nestlings were weighed and measured. Within 2 days of fledging, nest material was removed from nest boxes and enumerated for adult fleas and blow fly pupae. After including brood size and date of first egg as covariates in general linear models, no significant relationships were found between ectoparasite loads and nestling size, parental feeding rate, or nestling begging intensity. Our results suggest that nestling tree swallows were able to buffer the effects of naturally occurring ectoparasite loads without significant help from their parents. Low levels of virulence may have resulted from relatively benign weather during the study, low numbers of ectoparasites, selection on ectoparasites to avoid killing their hosts, and host defences.

Sibling competition affects individual growth strategies in marsh tit, Parus palustris, nestlings

How do different levels of sibling competition affect nestling growth strategies? We investigated this through the effect of different levels of per capita feeding rate on the average growth rate of nestlings and on individual growth strategies within broods. To manipulate sibling competition, we transferred marsh tit nestlings between nests creating broods with fewer (reduced) or more (enlarged) nestlings than originally. Mean mass decreased as brood size, and thus sibling competition, increased. This was due to a large difference in mass between the smallest young in each brood. The mass of the largest young did not differ significantly between the broods. In reduced broods, the largest and smallest nestlings had equal mass, whereas in enlarged broods the difference was large. In contrast, wing length close to fledging did not differ between the experimental broods. We conclude that the growth of the wing has priority over general increase in size. This depends on the risk of starving for nestlings unable to leave the nest when their most dominant sibling leaves. Thus, low intake rates induce a trade-off in the growth of different structures, leading subdominant nestlings to divert proportionally more resources to wing length growth at the expense of general size. Subdominant nestlings are thus facing both a food constraint, depending on parental feeding rate and number of dominant siblings, and a time constraint, depending on the growth rate of the largest sibling. Hence, to fledge successfully, subdominant nestlings will leave the nest at suboptimal masses with a likely increase in postfledging mortality.

Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows

Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows

Does large size make daughters of the blue‐footed booby more expensive than sons?

Summary 1. In species where size dimorphism emerges during parental care, individuals of the larger sex are presumably more expensive to produce than individuals of the smaller sex. 2. We evaluated whether female offspring of the blue‐footed booby, because of their larger size, require greater parental feeding expenditure than males. 3. A field experiment compared growth rates of sons and daughters when hand‐fed the same amount of food, and a descriptive field study compared the parental feeding rates to fledgling sons and daughters. 4. Females maintained greater rates of mass and ulna increase than males when fed the same amount of food. 5. First‐hatched chicks had higher probability to be fed than second‐hatched chicks. However, male and female fledglings were fed at similar rates by their parents. 6. No evidence that daughters of the blue‐footed booby receive a greater feeding expenditure than sons was found. Faster motor development of males in this facultatively siblicidal species might explain why they grow more slowly than females with the same food budget.

Properties of food loads delivered to nestlings in the pied flycatcher: effects of clutch size manipulation, year, and sex.

Experimental manipulation of the number of altricial offspring is supposed to modify parental expenditure in birds. In addition to the observed increase in parental feeding rate, it is also possible that the choice of prey or the size of load may change with the changing demand for food. Sexual differences in the provisioning response are also expected, on the basis of earlier studies. We examined the effect of brood size manipulation on choice of prey brought to nestlings and load size in the pied flycatcher. The composition and size of loads differed between years, possibly depending on varying availability of different prey types. Males responded to brood size enlargement by gathering heavier loads, whereas females showed no response. The alteration of load size in males was not explained by a larger number of prey items or mean prey size, but was a combination of these components. It is likely that males also increased their work rate in response to increased food demand at the nest. The absence of response in females might be because they are unable to increase work rate any further, or because food delivery rate in females can not be optimized by changing load properties.

Additional Notes on the Nesting Biology of Victoria's Riflebird Ptiloris victoriae

An earlier study (Frith & Frith 1995) reported details of the little-known breeding biology of Victoria’s Riflebird Ptiloris victoriae at two nests. Since then, four further nests have been found, only one of which had eggs laid in it (a clutch of two) and fledged two young. Here we compare our observations of parental incubation attendance, feeding rates, nestling periods and diet at a nest containing two young with our previous observations of a nest with only one young in it. We also compare the structures and materials used in five nests.

Fledgling care and male parental effort in the Hooded Warbler (Wilsonia citrina)

We followed family groups of Hooded Warblers (Wilsonia citrina) from hatching through to fledgling independence to determine (i) the duration and extent of parental care of fledglings, (ii) the extent of brood division, and (iii) whether male parental effort in caring for nestlings predicts male effort in caring for fledglings. The 9-day nestling period of Hooded Warblers was followed by 4 – 6 weeks of further parental care of fledged young. Parental feeding rates increased from hatching to when the young fledged from the nest, and males fed nestlings significantly more than females did. At the fledgling stage feeding rates to fledglings were significantly higher than at the nestling stage, but there was no difference in feeding rates between the parents. Parents usually divided the brood of fledglings equally, so that each parent assumed full and exclusive care of a subset of the brood. However, many females (45%) initiated a second brood and the male assumed care of the entire first brood at the time when his mate began incubating. The proportion of feeding trips to nestlings made by the male was not predictive of his subsequent effort in the care of fledglings. Exclusion of the fledgling care period in studies of parental investment may give a biased picture of overall investment on the part of both male and female parents.

The effect of ectoparasite nest load on the breeding biology of the Penduline Tit Remiz pendulinus

In this study we investigated the importance of ectoparasite load in the nest on the breed‐ing system of the Penduline Tit Remiz pendulinus, examining the effect of mite abundance in the nest on mate choice, reproductive success and parental effort. The two most common ectoparasites were the Northern Fowl Mite Dermanyssus hirundinis and the Northern Feather Mite Ornithonyssus sylviarum. The results show that mite load is important in mate choice but has no adverse effect on reproductive success. The results also indicate that infestation level is related to the quality of the male (mask‐width). Parental feeding rate was negatively related to mite load. This relationship indicated that Penduline Tits did not compensate for higher parasite loads by increasing feeding but rather reflected the con dition of the parent and its investment in self‐maintenance behaviour.

Proximate control of siblicide in cattle egrets: a test of the food-amount hypothesis

Avian sibling aggression plays an important role in controlling food distribution among nest mates. The food-amount hypothesis predicts that the amount of food obtained by siblings acts as a proximate cue controlling their level of aggression. The importance of this cue to cattle egrets (Bubulcus ibis) in Oklahoma was evaluated by studying parental feeding rates, food distribution among nestlings, and nestling aggression in three-chick broods [A-(oldest), B-, and C-chicks]. We compared nests in which siblicide occurred to nests where all three chicks survived (nonsiblicide nests). Relative to nonsiblicide nests, siblicide nests received decreasing amounts of food as the day of siblicide approached. Similarly, aggression levels of all three chicks in siblicide nests increased significantly compared with nonsiblicide nests, with most of the aggressive behavior involving B- and C-chicks. As a result, on a per-day basis, food amount and aggression exhibited a strong, negative correlation, thus providing support for the food-amount hypothesis. Though the total amount of food delivered to siblicide nests declined on the days prior to siblicide, the amount of food received by A-chicks in these nests did not. Relative to nonsiblicide nests, A-chicks in siblicide nests received an increased share (percent of volume) of the food delivered at the expense of C-chicks, with the percent remaining the same for B-chicks. The percentage of food B-chicks received the day after siblicide increased significantly from that received the day before siblicide, with no change occurring in either the amount or percentage of food received by A-chicks; clearly, B-chicks were the beneficiary of their aggressive actions that resulted in the death of C-chicks. We provide evidence supporting the hypothesis that aggression is proximately linked to food amount, possibly by a relatively simple cue such as hunger.

Great Crested GrebePodiceps cristatuschick mortality in relation to parental fishing

Chick mortality, prey size delivery and parental feeding rate of Great Crested Grebes were studied on ponds differing in fish species, densities and biomass on a fish farm in the south-east of the Netherlands. Chick mortality was highest during the first 2 weeks of life. Our results showed that amongst chicks younger than 3 weeks old, the rate of biomass intake per brood was correlated with the estimated prey abundance. Chick survival was highest amongst broods which received more food per unit time. Prey size increased as the young grew older, but older chicks still received very small items. On Carp ponds, parents delivered more prey per unit time to small young than on RoachlRudd ponds, but the rate of fish biomass delivery did not vary among pond types. This is because on average fish caught at Carp ponds were smaller than at RoachlRudd ponds. Presumably parental fishing opportunities in combination with prevailing weather conditions determine partial brood loss in Great Crested Grebe chicks.

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

AbstractThe 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.

Intersexual variation and factors affecting parental care in Western Bluebirds: a comparison of nestling and fledgling periods

We compared factors affecting parental feeding rates in Western Bluebirds (Sialia mexicana) between the nestling and fledgling periods to evaluate intersexual variation in parental care. Parents did not adjust the frequency of feeding visits between modal (five young) and below-modal (four or less young) broods during the nestling period. The frequency of parental feeding visits also was not significantly affected by offspring age during the nestling period. Males and females exhibited no significant differences in provisioning offspring, although males maintained a constant level of care throughout the nestling period, whereas females increased feeding visits following the brooding period. During the fledgling period, offspring from below-modal broods were fed at higher rates with increasing age than offspring from modal broods. Broods remained together (siblings averaged 8 m apart) within 200 m of the nest box for a week after fledging. As fledglings became more mobile, they would pursue parents while parents were foraging; parental feeding rates thus tended to increase with fledgling age and distance moved from the nest. Offspring sex did not influence parental care during the fledgling period. Both adults fed fledglings, with males taking sole care of fledglings if females initiated a second clutch soon (7–10 days) after fledging of the first brood. Parental feeding rates increased by 60% during the fledgling period compared with the nestling period. No evidence for brood division during the fledgling period was found. Although brood division represents one way of reducing energetic costs attributable to feeding fledglings, Western Bluebirds exhibit an alternate behavior in which the energetics of raising a brood are shared equally between the parents throughout both the nestling and fledgling periods. This is further facilitated by a close association of young during the fledgling period that may reduce energetic costs related to locating and feeding young.

Begging Behavior in Budgerigars

AbstractFive hypotheses about relationships between begging rates, feeding rates and other variables were investigated in captive budgerigar nestlings from 23 days post‐hatch to fledge date (Period 4). Within families, nestlings that begged more frequently during Period 4 were fed more often by their parents, but there was no indication that nestling weight on day 23 was related to begging rates in the subsequent growth interval. Instead, last‐hatched nestlings begged more than their older siblings. Last‐hatched nestlings were not “undersized” at the beginning of Period 4 relative to their siblings, and they experienced less competition than their siblings had at comparable ages. Even so, last‐hatched budgerigars begged more often, were fed more often and fledged at heavier weights than their older nestmates.Across families, there was a strong positive relationship between average Period 4 begging rate and average parental feeding rate, but this relationship was much weaker when brood sex ratio was taken into account: female‐biased broods had much higher begging and feeding rates than male‐biased broods. Brood size was related to begging, with higher ratios of begging to feeding rates for family members than for single nestlings.Taken together, these results suggest that relationships between feeding and begging behavior in budgerigars are more complex than theoretical models have suggested. More studies of avian begging and feeding patterns are required before we can generalize about the control of parental food allocations in birds.

Effects of Experimental Manipulation of Testosterone Levels on Parental Investment and Breeding Success in Male House Sparrows

-Breeding male House Sparrows (Passer domesticus) were implanted with testosterone (T), the antiandrogen flutamide (F), or an empty capsule as a control (C). Parental feeding rates by C-treated males were high until nestlings reached 10 days of age, then declined significantly. This is the typical temporal pattern of parental behavior for free-living males. In contrast, F-treated males fed young at a high rate throughout the nestling stage, while T-treated males fed young much less frequently and were more involved in male-male competition during this period of time. There was a significant decrease in the breeding success of T-treated males resulting from increased starvation of their nestlings. Despite lowered levels of testosterone, F-treated males were able to maintain control of their nest boxes and exhibited normal sexual behavior. During the subsequent brood, breeding success of T-treated males again was reduced by nestling starvation. Our results demonstrate that high levels of testosterone inhibit the expression of parental care in male House Sparrows. Moreover, they suggest that the typical pattern of testosterone levels in males (high when mate guarding and low when feeding young) represents an optimal compromise between allocation of effort to male-male competition vs. parental care. Received 10 July 1986, accepted 1 March 1987. CORRELATIONAL and experimental studies on House Sparrows (Passer domesticus) have suggested that the activities of breeding males represent a trade-off between investment in malemale competition vs. parental care. In males, circulating levels of testosterone reflect this trade-off, being elevated when male-male competition is high and low when parental investment is high. We have suggested that this pattern maximizes an individual's overall reproductive output, even if it results occasionally in a reduction of fecundity (Hegner and Wingfield 1986a, 1987). In this study, we tested experimentally whether the variable pattern of male investment represents an optimization by artificially altering that pattern. This was achieved by altering the endocrine and behavioral state of males with subcutaneous hormone implants. We tested specifically whether elevated levels of testosterone during the last portion of the nestling stage, the interbrood interval, and the egglaying stage are critical for (1) defense of the I Present address: Department of Zoology, NJ-15, University of Washington, Seattle, Washington 98195 USA. nesting site, (2) normal sexual behavior, and (3) successful mate guarding. We also tested (4) whether lowered levels of testosterone during incubation and the early portion of the nestling stage are necessary for the expression of parental care.

Sexual selection and variation in reproductive strategy in male yellow warblers (Dendroica petechia)

Male yellow warblers (Dendroica petechia) exhibit extensive variation in the amount and conspicuousness of the sexually distinctive brown streaking on the breast. We investigated this intraspecific variation in degree of sexual dichromatism to see if male plumage rank (essentially the amount of brown streaking) is correlated with the amount of reproductive effort allocated to parental investment, as sexual selection theory would predict. As predicted, the average rate of feeding visits to the nest by males was negatively correlated with the plumage rank of the male in 1982 (Fig. 1) and 1983 (Fig. 2), and varied little between years or among study areas. Within one study area, the higher nest visit rate of dull (low plumage rank) males was correlated with higher nestling growth rates. But in the other two study areas, where bright (high plumage rank) males predominated, nestlings of bright males tended to have the highest growth rates despite minimal nest visit rates. Thus, overall there was no correlation between male plumage rank and nestling growth rate, a potential index of relative reproductive success, in either year (Figs. 3 and 4). This overall equal nest success likely helps to maintain the behavioral and plumage polymorphism. Since we could find no evidence that the high nestling growth rates of bright males were due to an adjustment of female parental effort to compensate for low male parental effort, there must be some other benefit of being bright which contributes to nest success. To address this, we used the relationship between parental feeding rates and nestling growth rates for each nest as an index of relative territory quality. This analysis suggests that bright males generally occupy the best territories available, possibly because they are more aggressive in obtaining and defending them than dull males. Dull males appear to be relegated to poorer territories, where an increase in male parental contribution would be necessary to achieve high nestling growth rates. We propose that different males are using alternative but evolutionarily stable reproductive strategies, in a way that is consistent with the predictions of sexual selection theory. Allocation of limited reproductive effort to parental investment decreases as sexual dichromatism increases, which probably reflects an increased investment in intermale competition for the best territories.

Parental Care of Fledged Young, Division of Labor, and the Development of Foraging Techniques in the Northern Wheatear (Oenanthe oenanthe L.)

Abstract The care of fledged young by parents and the interactions between parents and young were studied in seven broods of Northern Wheatears (Oenanthe oenanthe L.) in an agricultural area near Uppsala, central Sweden. Time budgets of young and the development of foraging skills were also quantified. Young of the same brood were observed out of the nestholes on the 15th or 16th day after hatching. The parents did not divide the brood until day 3 or 4, day 1 being the 16th day after hatching (assuming that all young fledged on the 15th day). Full stability of family units, with no transfers of responsibility for feeding specific young, was achieved on days 3-8. Both parents fed their respective groups of young at different sites, and young of the same family unit appeared to be aggregated in the territories. They perched nearer to each other on average than to young fed by the other parent. These results support the hypothesis that a division of labor in altricial birds has evolved to allow parents to locate their young more easily and to reduce travel distances between sites at which prey are captured and the locations of young. Young wheatears depended on their parents for 2 weeks after leaving the nest. During that time, they became more active and mobile, spent less time calling and waiting for the parents to feed them, chased their parents more intensively to obtain food, and spent more time foraging. The marked increase in the chasing frequency of young after the first week coincided with a marked decrease in parental feeding rates and in the responsiveness of the parents to the begging calls of the young. Young also greatly increased their foraging activity after day 10, when parental feeding rates dropped to very low levels. These data support the hypothesis that parental reluctance to feed the young determines the onset of fledgling independence. Rates at which young attempted to capture prey and the proportion of successful attacks increased with age. Foraging techniques that are more dependent on flight performance (aerial hawking, perch-to-ground sallying) appeared later and were used less by the young than was ground-gleaning. There was a negative relationship between the intensity of chasing by the young and their capture success rates during different hours, which suggests that they switched between chasing the parents and self-feeding, depending on which was the most profitable strategy at the moment.

Brood reduction and brood division in coots

The probability of starvation of chicks increases through hatching order in broods of the coot, Fulica atra. After hatching chicks accompany, and are fed by, parents as they swim around the territory. The time that chicks are able to spend outside the nest increases rapidly with age, so that the earlier hatching chicks gain a feeding advantage over the later. Starvation of chicks occurs within 4–5 days of hatching. Even after this initial mortality there persist large differences in the parental feeding rates of individual chicks within a brood. These do not correlate with age and do not seem to be the result of sibling competition. Instead, the parents regulate which chicks accompany them on foraging trips and therefore actively maintain feeding differences within the brood. Chicks cannot counter this parental regulation and the least fed of the brood grow more slowly in spite of an increased self-feeding effort. The possible functions of this parental behaviour are discussed.

Size, organic composition, and energy content of Leach's storm-petrel (Oceanodroma leucorhoa) eggs with reference to position in the precocial–altricial spectrum and breeding ecology

Leach s storm-petrel eggs are very similar in composition to those of birds whose young develop precocially. In comparison with altricial species, eggs are relatively large (22% of adult mass), contain large yolks (41% of fresh egg contents) and have high yolk to albumen ratios. As in other precocial species, water content was low, making up 70% of the whole egg, 87% of the albumen, and 50% of the yolk, but accounted for much intraspecific variation in egg mass. The low water content is notable in view of the petrel's long incubation period, though low porosity of the eggshell and high humidity in the nest burrow must help the embryo conserve water. High lipid levels in the yolk (27%) are similar to those of precocial birds. Fresh yolk and albumen each contained 14% protein. About 80% (55.3 ± 2.5 kJ) of the total energy in the egg (60.7 ± 3.8 kJ) was contained in the yolk. The energy density of wet egg contents (7.27 ± 0.48 kJ/g) falls in the range of precocial birds. The egg's high energy content can be explained in terms of the maintenance requirements of the embryo during the long incubation period and the precocity of the hatchling. On the basis of standard metabolic rate estimates and interspecific comparisons, it does not appear to be energetically costly for a female to produce an egg. Single egg clutches and absence of relaying following egg loss suggest that the pelagic feeding ecology of Leach's storm-petrel imposes severe constraints on parental feeding rates and meal size, which effectively limit viable brood size to one.

Parental feeding rate in relation to begging behavior in asynchronously hatched broods of the great tit Parus major

Variations in the begging behaviour of the nestlings of altricial birds can provide the parents with information about the nestlings' nutritional needs and thus influence the parental feeding rate. In a series of four experiments, the stimulus situation encountered by great tits on their feeding visits to the brood was manipulated to explore its effect on feeding rate.