Brood Division Research Articles

Patterns of parental care and movement in divided broods of golden‐winged warblers

Post‐fledging brood division is a poorly understood, yet widespread suite of avian behaviours that includes both division of parental care and spatial division of a brood. For most species, the differences in parental care between adult males and females and the behavioural mechanisms explaining spatial patterns of brood division are unknown. We studied brood division in golden‐winged warblers Vermivora chrysoptera to describe the spatial and behavioural characteristics of brood division and assess hypotheses describing the potential benefits of brood division. Female golden‐winged warblers are known to travel farther from their nests than males within the post‐fledging period, although the mechanism resulting in this spatial pattern is unknown. From 2010 to 2012, we monitored radio‐marked golden‐winged warbler fledglings from fledging until independence from adult care at three sites in the western Great Lakes region of North America. We observed no significant differences in provisioning, parental attendance, daily distance traveled and fledgling begging between male‐ and female‐reared sub‐broods. We also did not observe a relationship between parental sex and fledgling sex or mass. However, female‐reared sub‐broods exhibited a unique period of relatively consistent directional movement on days 8–10 after fledging, which resulted in females traveling farther from the nests than males. Our observations were not fully consistent with any previously proposed hypotheses about the benefits of brood division. Brood division is a complex behaviour that may have a suite of benefits, including predation defense and provisioning efficiency, that are not fully understood.

Post-fledging brood and care division in the roseate tern (Sterna dougallii)

Extended post-fledging parental care is an important aspect of parental care in birds, although little studied due to logistic difficulties. Commonly, the brood is split physically (brood division) and/or preferential care is given to a subset of the brood by one parent or the other (care division). Among gulls and tern (Laridae), males and females generally share parental activities during the pre-fledging period, but the allocation of parental care after fledging is little documented. This study examined the behaviour of male and female roseate terns (Sterna dougallii) during the late chick-rearing and early post-fledging periods, and in particular the amount of feeds and the time spent in attendance given to individual chicks/fledglings. Pre-fledging parental care was biparental in all cases. Post-fledging parental care was dependent on the number of fledglings in the brood. Males and females continued biparental care in clutches with one surviving fledgling, while in two-fledgling clutches, males fed the A-fledgling while females fed the B-fledgling. Overall, there was no difference in attendance, only in feeds. This division of care may be influenced by the male only being certain of the paternity of the A-chick but not by chick sex.

Patterns of brood division and an absence of behavioral plasticity in a neotropical passerine

Studies of parental behavior in various habitats provide an opportunity to gain insight into how different environments may mold strategies of parental care. Brood division by parents has been hypothesized to occur facultatively within and among species. Brood division occurs when each parent cares for specific offspring within a brood. We studied brood division in a neotropical passerine, the western slaty antshrike (Thamnophilus atrinucha). Our results present a unique picture of a highly specialized example of avian brood division. Division was a fixed behavioral pattern in the population studied: all broods divided by fledging and remained divided during the entire post-fledging period. Brood division before fledging, a previously unreported phenomenon, occurred in 40% of nests observed. Parents that preferentially fed a certain offspring (defined as their focal offspring) in the nest fed the same individual after fledging. Each parent fed only its focal offspring in broods of one and two. The male parent cared for the heavier offspring and the first offspring to leave the nest. Siblings were segregated spatially during the time of highest predation risk. These observations suggest that a consistently high risk of predation on offspring has favored initial spatial segregation and inflexibility of brood division behavior in this species. Factors other than predation risk alone may explain the observed patterns of long-term, perfect brood division. Because high predation is common and relatively predictable in the tropics, selection for fixed brood division may be stronger in tropical birds than in the temperate zone.

Extreme gender-based post-fledging brood division in the toc-toc

The possibility that parents of one sex may preferentially invest in offspring of a certain sex raises profound evolutionary questions about the relative worth of sons and daughters to their mothers and fathers. Post-fledging brood division-in which cacti parent feeds a different subset of offspring-has been well documented in birds. However, a lack of empirical evidence that this may be based oil offspring sex, combined with the theoretical difficulty of explaining such an interaction, has led researchers to consider a gender bias in post-fledging brood division highly unlikely. Here we show that in the toc-toc, Foudia sechellarum, postfledging brood division is extreme and determined by sex; where brood composition allows, male parents exclusively provision male fledglings, whereas female parents provision female fledglings. This is the first study to provide unambiguous evidence, based on molecular sexing, that sex-biased post-fledging brood division can occur in birds. Male and female parents provisioned at the same rate and neither offspring nor parent survival appeared to be affected by the sex of the parent or offspring, respectively. The current hypotheses predicting advantages for brood division and preferential care for one specific type of offspring are discussed in the light of our results.

In a songbird, the black redstart, parents use acoustic cues to discriminate between their different fledglings

Several studies on parental investment in territorial songbirds have reported the existence of brood division. This is a type of postfledging care in which each parent has long-term feeding preferences for different young within a brood, creating two family units. Recent theoretical work indicates that conflicts between individuals should select for brood division. However, little is known about the mechanisms involved in the onset and maintenance of this behavioural strategy. Given the high rate of fledglings' begging calls, we hypothesized that acoustic discrimination could explain the stability of feeding preferences at a proximate level. In a 3-year field study, we recorded the responses of parent black redstarts, Phoenicurus ochruros, a territorial songbird, to playback of the begging calls of fledglings fed by the male and by the female. Parents responded more to the calls of the fledglings that they preferentially fed. A principal component analysis of the calls suggested that parents may recognize individual offspring. To our knowledge, this study provides the first evidence that a bird can acoustically discriminate between two categories of its own offspring: those that it preferentially feeds and those fed by the other parent.

Parental care and brood division in a songbird, the black redstart

AbstractSexual conflict over parental care can be mediated through differences in male and female overall feeding rates, brood division or both. At present, it is not clear whether post-fledging brood division occurs due to sexual conflict over parental investment or is due to bi-parental cooperation, e.g. increase offspring fitness. We provide evidence suggesting that brood division in the black redstart, Phoenicurus ochruros is due to sexual conflict. Males and females had similar feeding contributions during the nestling stage, which is common for most passerine species. After fledging, each parent showed long-term feeding preferences for particular chicks within the brood. In most cases (74%; 17/23) both parents provided care but males tended to feed less fledglings than females did and in about a quarter of cases (26%; 6/23) females fed the whole brood by themselves. The relative amount of male to female post-fledging feedings showed a significant negative relationship with the proportion of fledglings cared for exclusively by the male. These results suggest (1) a close link between the amount of parental care and brood division; (2) sexual conflict can be mediated through brood division; (3) female redstarts appear to loose this conflict more often than male redstarts, with in the extreme cases males showing post-fledging brood desertion. A literature review shows brood division to occur in at least a dozen of songbird species but male black redstarts have the lowest relative post-fledging parental investment, expressed either as feeding rates or number of chicks in care.

Long-term brood division and exclusive parental care in a cooperatively breeding passerine

In some species of birds, individual adults feed different subsets of the brood after the young have left the nest. However, few studies have shown that such ‘brood division’ represents long-term separation into subfamilies, rather than short-term biases in care, and the function of brood division is unknown. Most functional hypotheses assume that brood division is an adult adaptation to increase reproductive success; others suggest that fledglings are responsible for brood division, or that brood division is the outcome of conflicts of interest within families. We tested for long-term brood division in the white-browed scrubwren, Sericornis frontalis, a cooperatively breeding passerine, and assessed functional hypotheses, using behavioural, morphological and molecular evidence. We found that 71% of scrubwren broods became divided in the second week after fledging, and remained divided for the following 4–5 weeks of care. Furthermore, most individual young were fed almost exclusively by a single adult, even in undivided broods and broods of one. Brood division did not arise through adults caring for young of a specific sex, nor did genetic paternity explain division. Tests of other hypotheses were indirect, relying for example on testing mechanisms rather than predictions. We rejected the hypotheses that brood division was primarily an adaptation to reduce the mean or variance in predation, or that it was likely to increase the rate at which young were provisioned. Fledglings probably had an active role in maintaining brood division, with fledglings that had been biggest in the nest tending to be fed by adults that had fed nestlings at the greatest rate. This suggests that the most dominant fledgling may sequester the care of the best feeder. We also found evidence that brood division might be an adult adaptation to reduce the effects of sibling competition, or that it might arise through conflicts of interest among adults. We further suggest that social specialization, resulting from learning about a particular individual, might bring additional advantages to long-term brood division. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Postfledging parental care in Savannah sparrows: sex, size and survival

We investigated postfledging parental care in a philopatric population of Savannah sparrows,Passerculus sandwichensis , breeding on Kent Island, New Brunswick, Canada in an effort to understand the factors influencing adult birds' decisions about parental investment in offspring. Brood division was not based on offspring sex: male and female parents were equally likely to care for sons or daughters. The total duration of parental care, from hatching to independence, was similar for sons and daughters (median=23 days), regardless of the sex of the care-giving parent. The duration of parental care also corresponded closely to the time required for juveniles to acquire basic foraging skills. Despite high levels of extrapair paternity, male Savannah sparrows invested as much in postfledging care and were as effective as females in caring for fledglings, based on recruitment of fledglings into the breeding population the following year. Male parents were more likely to care for smaller fledglings and for offspring from early broods (presumably to enable females to dedicate their efforts towards second clutches). Caring for fledglings was costly for parents: survivorship decreased as a function of the duration of postfledging parental care and the number of fledglings cared for. Parental survivorship, however, was not affected by the sex of the fledglings cared for. This study suggests that sex-biased provisioning may be unlikely except in species with strongly sexually dimorphic offspring, biased offspring sex ratios and sex-biased natal dispersal. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Parentally biased favouritism: why should parents specialize in caring for different offspring?

'Parentally biased favouritism' occurs when the two parents differentially care for individual offspring or kinds of offspring. Examples in birds include brood division and differential investment by the two parents in relation to the size or sex of the offspring. This paper uses mathematical models to investigate which ideas can, in theory, explain parentally biased favouritism. One previous explanation is that the parents differ in their cost of reproduction and that the parent who consequently invests least concentrates its care on the more valuable offspring. However, a mathematical model predicts the total care given by each parent and received by each offspring, not how much each parent cares for each offspring, and hence does not explain parentally biased favouritism. Parentally biased favouritism towards particular types of offspring can be explained by a difference between the parents in the benefits of caring for a given type of offspring or in the effort incurred in providing care to a given type of offspring, but then it is extreme, with at least one of the parents providing care to only one type of offspring. Parentally biased favouritism towards particular individual offspring (brood division) can be explained by parent-offspring conflict or sexual conflict.

Breeding behaviour, clutch size and egg dimensions of Neospiza buntings at Inaccessible Island, Tristan da Cunha

Inaccessible Island, Tristan da Cunha, supports two colour morphs of Tristan Buntings, Nesospiza (a.) acunhae, Wilkins' Buntings, N. (wilkinsi) dunnei, and interspecific hybrids between Tristan and Wilkins' Buntings. Breeding takes place in the austral summer (November-February). The onset of breeding (mid-November to early December) was similar in 1989/90 and 1999/2000, but may commence earlier in some years. The larger and rarer Wilkins' Buntings started breeding 1–2 weeks earlier than Tristan Buntings. Basic breeding biology was similar among all populations at Inaccessible Island. Females undertook all nest construction, building relatively large, open cup nests on the ground or up to 1.2 m up in dense tussock gross, Spartina arundinacea. Clutch size was two, or occasionally one, eggs, and did not differ between taxa (mean 1.81 ± 0.40). For two-egg clutches, egg size differed by 7–11% on average. In all cases where laying sequence was known, second-laid eggs were smaller than first-laid eggs, and larger eggs almost invariably hatched first. Egg size was related to body size, and upland Tristan Buntings laid significantly larger eggs than lowland Tristan Buntings, Nesospiza eggs are similar in size to those of other finch-like members of the tribe Thraupini, but within the genus egg size increases more slowly relative to body size than expected. This pattern is shored by Darwin's Finches; we infer that evolution in body size has outpaced evolution in egg size. Wilkins' Bunting eggs were more elongate than those of Tristan Buntings or hybrids, which mirrors a trend for egg elongation to increase with body size among finches. Incubation lasted 17–18 d and was solely by the female. Chicks remained in the nest for 18–22 d, averaging slightly longer for larger taxa. After fledging, juveniles were fed by the parents for up to 11 weeks, during which time they remained in the natal territory. Brood division occurred among pairs that raised two chicks, with a tendency for male parents to care for female offspring and vice versa. The long period of post-fledging parental care prevented pairs raising more than one brood each year, although repeat clutches were common following breeding failure.

Allocation of Male Parental Care in Relation to Paternity Within and Among Broods of the Common Yellowthroat (Geothlypis trichas)

The relationship between male parental care and paternity has been investigated in a number of avian species, but in many cases the influences of confounding factors, such as variation in male and territory quality, were not addressed. These sources of variation can be controlled for by making within‐male comparisons between successive broods or within‐brood comparisons between groups of fledglings in a divided brood. We studied the relationship between male parental care and paternity in the common yellowthroat (Geothlypis trichas) at three levels: between groups of fledglings in divided broods, between first and second broods of the same pair, and among all broods in the population. In this study we proposed three hypotheses: first, males in double‐brooded pairs should provide relatively more parental care to broods in which they have higher paternity; secondly, after fledging and brood division, males should provide more care to related offspring; and finally, among all broods in the population, paternity should be related positively to male parental care. Brood division occurred in many of the broods studied; however, broods were not divided according to fledgling size or paternity. Furthermore, within divided broods, males fed within‐pair and extra‐pair fledglings at similar rates. For sequential broods of the same pair, male feeding rates were not associated with differences in paternity between broods. Among all broods in the population, males did not provide relatively less care to broods containing unrelated young. The lack of a relationship between male parental care and paternity suggests that either males cannot assess their paternity or the costs of reducing male parental care outweigh the benefits.

MOVEMENTS AND SURVIVAL OF LARK BUNTING FLEDGLINGS

Abstract We quantified post-fledging pre-independence behavior and survival in Lark Buntings (Calamospiza melanocorys) using radio-telemetry. Brood division was recorded in six broods and was maintained throughout the observed fledgling care period. Chicks were capable of short flights (up to 25 m) by fledgling day 6 and longer flights (to 100 m) by fledgling day 13. During the first three weeks after fledging, juveniles moved as far as 800 m from nests. Nine of 23 (39%) monitored fledglings died within 15 days of fledging, primarily due to predation by raptors. Daily survival rates were 0.953 ± 0.019 for fledgling days 0–9, 0.955 ± 0.038 for fledgling days 10–20, and 0.953 ± 0.015 for fledgling days 0–20. The probability of surviving fledgling days 0–20 was 0.367. More quantification of juvenile survival is clearly needed to understand the role of post-fledging mortality in source-sink dynamics. Los Movimientos y Supervivencia de los Volantones de Calamospiza melanocorys Resumen. Cuantificamos la conduct...

How White-Throated Magpie-Jay Helpers Contribute during Breeding

We investigated the mechanisms by which helpers contribute to breeder reproduction in a Costa Rican population of White-throated Magpie-Jays (Calocitta formosa). Helpers provided a substantial proportion of all feedings to female breeders and their offspring, proportionately more than most species of cooperatively breeding New World jays. Breeding males typically fed breeding females and offspring less frequently than expected, however. There was little evidence of brood division in the sense of individual provisioners (breeders or helpers) preferentially feeding particular fledglings within a brood. The rate of provisioning per recipient increased as a function of group size only during the pre-incubation period (provisioning of the laying female). Provisioning rates per nestling and per fledgling were not correlated with group size, and the number of offspring fledged per successful nest did not increase with group size. Helpers did reduce the provisioning burden on breeders, however, and occasionally were the primary care-providers of fledglings, which allowed breeders to renest. More successful nests were produced in groups with many helpers than few, resulting in more fledged young per year. Mechanisms contributing to this "helper-effect" included more nesting attempts per year and a higher likelihood of renesting after a successful attempt. We conclude that the contributions of magpie- jay helpers increased breeder fitness, and the indirect and direct benefits gained by helping probably favored its expression by nonbreeding group members.

Brood division in birds in relation to offspring size: sibling rivalry and parental control

In some altricial birds with biparental care, it is the female, and in others the male, that provides more food to the smallest offspring within the brood. Many hypotheses have been proposed to account for such puzzling patterns of parental care. A parsimonious explanation is that no difference exists between the parents in priority of care but that differences arise simply from sibling rivalry, with dominant chicks trying to position themselves closest to the parent that provides most care (the sibling rivalry hypothesis). A refinement of the idea is that parents use the way they approach the chicks to counter selfish offspring and in this way control allocation of care (the parental approaching hypothesis). A comparison across species suggested that female care of the smallest chick within a brood is the ancestral and most common pattern. However, strong variation exists within single populations. In one species, the American robin,Turdus migratoriusthe sibling rivalry hypothesis and the parental approaching hypothesis were both supported because in broods where males provided more care than females, the largest chick was predominantly fed by the male whereas the smallest chick was predominantly fed by the female. When the male provided less care than the female, an opposite result was found. The same patterns of allocation of care also seemed to exist when chicks were quite immobile just after having left the nest and when their positions were experimentally controlled, suggesting parental control.

Brood Division Is Associated with Fledgling Dispersion in the Bluethroat (Luscinia s. svecica)

-In many bird species with biparental care, each parent takes the exclusive care of some of the young after fledging. Some of the hypotheses that have been put forth to explain brood division behavior state that it is advantageous for a particular parent to care for a particular type of young, e.g. with respect to sex, size, or parentage. Other hypotheses claim a benefit to the parents (e.g. reduced foraging costs or risks of predation) only when the young are spatially dispersed. In this paper, we describe brood division in a Norwegian population of Bluethroats (Luscinia s. svecica). In general, brood division arose once the young became spatially dispersed after fledging. The only exceptions to the rule occurred when the male was polygynous and provisioned the young at a low rate. No brood division was found when the young were still in the nest, nor when they were physically prevented from spacing out by an enclosure around the nest. Young fed by the same parent were more clustered than young fed by different parents. Experimental switching of young among single-parent groups suggested that parents were able to recognize individual offspring outside the nest. However, there were no indications that parents divided the brood by sex, size, or genetic parentage. Our data are consistent with hypotheses that assume a parental benefit from brood division when the young are spatially dispersed. Received 13 September 1996, accepted 7 April 1997. IN MANY BIRD SPECIES with biparental care, the parents divide the brood after fledging so that each parent takes sole care of some young (Skutch 1976). This phenomenon is known as brood division (Smith 1978, McLaughlin and Montgomerie 1985), and the association between a parent and its young is termed a family unit (Nolan 1978). Many reports on brood division are anecdotal and provide no data. However, some studies of brood division are more detailed and well documented (e.g. Smith 1 Address correspondence to this author. E-mail: j.t.lifjeld@toyen.uio.no 1978, Moreno 1984, Harper 1985, McLaughlin and Montgomerie 1985, Kopachena and Falls 1991). In many altricial species, particularly open nesters, the young leave the nest early (Maher 1964), often before they are completely developed and able to fly (Tinbergen 1939, Skutch 1976, Knapton 1978, Kopachena and Falls 1991). Early nest departure coupled with spatial dispersion of young is viewed as a strategy to minimize the risk of predation (Tinbergen 1939, Maher 1964, Willis 1972, Knapton 1978, Nolan 1978) and/or to help parents reduce the energetic costs of parental care (McLaughlin and Montgomerie 1989a,b). Spatial dispersion

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.

Lead and behavioral development: Parental compensation for behaviorally impaired chicks

Lead is ubiquitous in nature, and can affect behavioral, physiological, and intellectual development in humans and other animals. We used lead-induced behavioral deficits to examine the behavior of parents and young herring gulls in the Captree, NY, gull colony. Our objectives were to determine: a) If there were differences in the behavior, weight, and survival of chicks as a function of treatment; b) if parental behavior varied as a function of treatment; and 3) if there were differences in sibling competition and parent-young conflict between experimental nests (with lead-impaired chicks and control chicks) and control nests. We injected one chick in each of 22 nests (1–2 days of age) with lead acetate (100 mg/kg in sterile water) and injected its sibling with sterile saline, and compared behavior of parents and young (from 1–21 days postinjection). We also observed behavior of parents and chicks in 12 control nests in which chicks were handled similarly but were not injected. There were significant lead-induced differences in righting response, locomotion, thermoregulation, begging, and feeding behavior in the chicks; corroborating observations from the laboratory. Lead-injected chicks were less able to compete for food with their siblings, with a resultant significant difference by weight at 16 days of age. For experimental nests in which the weight difference was great, parents engaged in divided feeding of the brood. After one parent initiated feeding, the other parent walked a short distance away and began to call to and then feed the second, smaller chick. The extra parental care resulted in increased survival for the lead-injected chicks, and in their catching up to their siblings in weight by fledging. The results of this experiment indicate that lead induces behavioral deficits and growth retardation in gulls in nature, decreases survival at young ages, and that parents compensate for these behavioral and growth deficits by brood division for feeding chicks such that by fledging the chicks are no longer at a weight and size disadvantage. Parents are, thus, able to perceive a difference in body size and/or vigor of their offspring, and to behaviorally compensate partially for the lead-induced deficits.

An experimental study of brood division in white-throated sparrows

Parental care towards experimentally restrained white-throated sparrow, Zonotrichia albicollis, fledglings was examined for evidence of brood division. Brood division occurred in 14 of 17 broods and was characterized by distinct but overlapping preferences by parents for particular brood members. The combined efforts of the parents usually resulted in an even distribution of resources among the brood. However, in some cases, brood division caused some fledglings to receive more food than others. Within-brood variation in food received was correlated with the difference between parents in parental effort. Brood division was maintained by the location of the young for some parents and by the identity of the young for other parents. It is suggested that changes in brood mobility might necessitate a shift in the cues used to discriminate between fledglings in order for parents to maintain brood division through the post-fledging period.

Brood care in American robins: Implications for mixed reproductive strategies by females

Parental care of nestling and fledgling American robins, Turdus migratorius, was studied in eastern Ontario. There was no evidence of brood division prior to fledging but brood division was the predominant pattern after fledging. Females initiating second nests reduced their care of fledglings sooner than males. Once incubation began at second nests, males provided all the care for fledglings from the previous nest. A consequence of overlapping first and second nesting efforts is that care of fledglings from the first nest allows males little opportunity of mate guarding when their mates are initiating the second nest. Reduced opportunity for mate guarding is probably excerbated by the wide dispersal of fledglings at the time of egg laying at second nests. In spite of the apparent reduced opportunity for mate guarding, males fed nestlings in second nests as much as those in first nests. This result suggests that females initiating second nests may refrain from extra-pair copulations if their mates have proven themselves by the success of the first nest, because confidence of paternity ensures male parental care at the second nest. Information from the literature suggests that the mixed strategy by females of being willing to engage in extra-pair copulations when initiating first but not second broods may occur in other species with overlapping broods.

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.