Flexible parents: joint effects of handicapping and brood size manipulation on female parental care in Nicrophorus vespilloides

Parental care is highly variable, reflecting that parents make flexible decisions in response to variation in the cost of care to themselves and the benefit to their offspring. Much of the evidence that parents respond to such variation derives from handicapping and brood size manipulations, the separate effects of which are well understood. However, little is known about their joint effects. Here, we fill this gap by conducting a joint handicapping and brood size manipulation in the burying beetle Nicrophorus vespilloides. We handicapped half of the females by attaching a lead weight to their pronotum, leaving the remaining females as controls. We also manipulated brood size by providing each female with 5, 20 or 40 larvae. In contrast to what we predicted, handicapped females spent more time provisioning food than controls. We also found that handicapped females spent more time consuming carrion. Furthermore, handicapped females spent a similar amount of time consuming carrion regardless of brood size, whereas controls spent more time consuming carrion as brood increased. Females spent more time provisioning food towards larger broods, and females were more likely to engage in carrion consumption when caring for larger broods. We conclude that females respond to both handicapping and brood size manipulations, but these responses are largely independent of each other. Overall, our results suggest that handicapping might lead to a higher investment into current reproduction and that it might be associated with compensatory responses that negate the detrimental impact of higher cost of care in handicapped parents.     

Providing chicks with extra food lowers male but not female provisioning in the House Sparrow Passer domesticus

We assessed whether adult House Sparrows Passer domesticus adjusted their provisioning in response to an experimental increase in the nutritional condition of their nestlings. When we supplemented chicks directly with additional food, male parents, but not female parents, reduced their provisioning. The results for males, but not females, run contrary to a previous experiment in this species. In addition, female provisioning was positively associated with both brood size and the age of the brood. In contrast, whereas male provisioning was positively associated with brood size, males did not increase provisioning as their chicks grew older. Males, but not females, exhibited repeatability in their provisioning. Food supplementation had a larger positive effect upon nestling survival in smaller broods than in larger broods. Overall, there appear to be fundamental differences between males and females in how decisions regarding the level of parental investment in the current brood are made.     

Flexibility in the Foraging Behavior of Blue Tits in Response to Short‐Term Manipulations of Brood Size

Previous work suggests that short‐term changes in feeding rate are usually produced by the parent‐offspring interaction. However, few studies have properly tested this assumption. In this study, we attempt to explore the short‐term consequences of daily (within‐pair) brood size manipulations (reduced, original, and enlarged) on feeding behavior (provisioning rates, prey size, and prey type) of Mediterranean blue tits Cyanistes caeruleus. Total provisioning rates were lowest when broods were reduced in size and greatest when broods were enlarged. Mean prey size was also affected by the brood size changes: parents tended to bring larger prey when confronted with low brood demand reinforcing the view that a trade‐off exists between minimizing foraging time and maximizing food quantity. Such differences in feeding frequencies and the load sizes delivered may be explained by changes in the parents’ foraging tactic. Increase of brood size compelled parents to work harder and be less selective in prey choice; we found that stressed birds with a high level of feeding responsibility (hungry nestlings) opted to concentrate on more readily available food items (Tortricids). On the other hand, their immediate reaction when faced with a low level of feeding responsibility was to decrease this prey type in the diet, so that the percentage of other preys (Noctuids) in the diet increased. There was no intersexual difference in the way in which parents responded to the manipulation. In sum, our results revealed a flexibility in foraging strategies of blue tits to cope with changing scenarios, which supports the idea that provisioning behavior is largely governed by nestling demand.     

Parental care behavior in the monogamous,sexually dimorphic Madagascar paradise flycatcher: sex differences and the effect of brood size

I studied the parental care behavior of the Madagascar paradise flycatcher Terpsiphone mutata in northwestern Madagascar. I especially focused on feeding, brooding and vigilance behaviors. Feeding rate did not differ between males and females, but females spent more time at the nest than males. Females dedicated their time to brooding, while males perched on the nest and were vigilant. Both parents changed the feeding rate in relation to brood size, so the feeding rate per nestling was not different among nests of different brood size. Duration of brooding by females increased with decreasing brood size, suggesting that the Royama effect, the pattern of lower feeding rate per nestling in larger broods, did not apply in this study. Males spent more time on vigilance than females. Anti-predator vigilance by males should be important for nestling survival given the high predation pressure typical of this population. In conclusion, males provide considerable parental care probably to minimize nestling starvation and to avoid nest predation. My results are not consistent with the general pattern of less parental effort by males in monogamous, sexually dimorphic species.     

Diet of Starling Sturnus vulgaris nestlings on farmland: the importance of Tipulidae larvae

Capsule?Tipulidae larvae are a key resource for adult Starlings provisioning their young on lowland farmland.

Aims?(i) To describe Starling nestling diet on lowland farmland. (ii) To examine the effects of brood size variation and nestling age on Starling parental food provisioning.

Methods?Over 4 years, we observed parental food provisioning at 42 nests across 4 sites on lowland farmland in Oxfordshire, UK using nestbox video recorders.

Results?Tipulidae larvae were the most frequent prey item recorded in provisioning loads (52%), the next most frequent were winged insects (11%), then Coleoptera larvae (6%), Lepidoptera larvae (5%) and Lumbricidae (5%), with 21% of prey unidentified. Estimates of prey lengths, dry mass and total energy content also confirmed that Tipulidae larvae were the key prey source. Generalized linear mixed-effects models showed that larger broods received fewer Tipulidae larvae per nestling per day and that the proportion of Tipulidae larvae in the diet did not vary with brood size or nestling age.

Conclusion?Our results support the idea that Tipulidae larvae are the primary dietary item for nestling Starlings on lowland farmland.     

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. Received: 18 December 1997 / Accepted: 1 March 1998     

Parental behaviour of Spanish Imperial Eagles Aquila adalberti: sexual differences in a moderately dimorphic raptor

Capsule The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks.

Aims To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding).

Methods Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences.

Results Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chick-rearing (to feed the chicks). Females were responsible for most of the incubation, nest-building (during incubation and chick-rearing), brooding, shading and feeding of chicks. Nest attendance by females decreased over time. In both sexes, food provisioning increased with brood size.

Conclusion Intersexual differences are discussed in the context of the reversed sexual size dimorphism and parental investment strategies. We suggest that in Spanish Imperial Eagles reversed sexual size dimorphism is best explained by the prey capture difficulty hypothesis, than by parental role division during reproduction.     

How different provisioning strategies result in equal rates of food delivery: an experimental study of blue tits Parus caeruleus

Food provisioning in birds requires a considerable amount of time and usually has to be traded-off against other parental and non-parental activities. I investigated experimentally the rate at which blue tit Parus caeruleus parents deliver food to their brood after a change in food availability. The main argument behind this study is that parents enjoying an additional food source may use less time for self-feeding and therefore use more time for food provisioning. This could increase the rate at which food is brought to the nest. However, a prey choice model that takes the energetic needs of the parent into account allows for the possibility that the food-supplemented parents would deliver the same amount of food by increasing prey size (through an increase in prey selectivity) and reducing visit rate. The field data indicate that the parents changed provisioning strategy when food-supplemented: they fed the chicks natural food less frequently, but brought larger larvae. On the whole, delivery rate of natural food was the same or lower than in controls. The results suggest that food-supplemented parents used the time saved to increase their degree of food selectivity. When the gains from an increased delivery rate are not worth the increased costs (mainly resulting from an increased visiting rate), the parent with low energetic need may increase selectivity to provide the same amount of food to the brood as the unmanipulated parent, but at a lower cost.     

Breeding behaviour and time-activity budgets of Bonelli’s Eagles Aquila fasciata: marked sexual differences in parental activities

ABSTRACT

Capsule: Differences in parental investment between sexes and stage of the breeding period were found in Bonelli’s Eagles Aquila fasciata.

Aims: To describe the sexual differences in parental behaviour of Bonelli’s Eagles and to assess the sex-specific pattern of variation in parental investment in relation to the breeding period.

Methods: Between 2006 and 2016, we monitored the parental behaviour of 11 pairs of Bonelli’s Eagles during the incubation and chick-rearing periods in southeastern Spain. Observations were made using 20–60× telescopes from points overlooking the territory at a distance of about 500–800?m from the nest.

Results: Our results reveal a marked division in parental duties in Bonelli’s Eagles. Females invested more effort in incubation, nest attendance, chick feeding and nest-building, while males contributed more to food provisioning. Nest attendance and feeding by females decreased with time, and both parents adjusted their provisioning effort in relation to nestling age. Most changeovers took place during the middle of the day, when male provisioning rates and temperatures reach their maximum.

Conclusion: Intersexual differences are discussed in the context of the prey capture difficulty hypothesis, which proposes that intra-pair prey differences, due to large sexual size dimorphism, should be particularly advantageous among raptors that pursue agile prey.     

Parental Sex Differences in Food Allocation to Junior Brood Members as Mediated by Prey Size

Individual offspring within a brood may receive different amounts of provisioning from the male and female parents. Some hypotheses suggest that this bias is the result of an active and adaptive choice by parents. An alternative hypothesis is that feeding biases arise as a result of a constraint of fitting large prey items into small gapes. In an experiment with pied flycatchers, Ficedula hypoleuca , we tested for sex-biased allocation to junior nestlings in asynchronous broods and whether this could be explained by active parental choice or by passive allocation according to prey size and gape size. In both control broods and broods with experimentally increased degree of asynchrony, prey types did not differ between parents but females brought smaller prey than males at younger but not older nestling stages. At younger but not older nestling stages, the majority of feeds to junior nestlings were from females, and the smaller nestlings consumed smaller prey than older siblings. However, there was no evidence of active preference of small nestlings by females as parents did not differ in the tendency to bypass a begging senior nestling in order to feed a junior nestling. Provisioning rates by females were lower than those by males when nestlings were young and we suggest that foraging time constraints caused by the need to brood offspring result in females bringing smaller prey than males. In turn, the larger prey brought by males was more often transferred to larger offspring after the smaller ones failed to swallow it. In such cases, 'preferential' feeding of small nestlings by females may simply be a passive side effect of foraging constraints and gape-size limitations.     

Energy expenditure, nestling age, and brood size: an experimental study of parental behavior in the great tit Parus major

A brood manipulation experiment on great tits Parus major was performedto study the effects of nestling age and brood size on parentalcare and offspring survival. Daily energy expenditure (DEE)of females feeding nestlings of 6 and 12 days of age was measuredusing the doubly-labeled water technique. Females adjusted theirbrooding behavior to the age of the young. The data are consistentwith the idea that brooding behavior was determined primarilyby the thermoregulatory requirements of the brood. Female DEEdid not differ with nestling age; when differences in body masswere controlled for, it was lower during the brooding periodthan later. In enlarged broods, both parents showed significantlyhigher rates of food provisioning to the brood. Female DEE wasaffected by brood size manipulation, and it did not level offwith brood size. There was no significant effect of nestlingage on the relation between DEE and manipulation. Birds wereable to raise a larger brood than the natural brood size, althoughlarger broods suffered from increased nestling mortality ratesduring the peak demand period of the nestlings. Offspring conditionat fledging was negatively affected by brood size manipulation,but recruitment rate per brood was positively related to broodsize, suggesting that the optimal brood size exceeds the naturalbrood size in this population.     

Diversionary feeding and nestling diet of Hen Harriers Circus cyaneus

Capsule: Diversionary feeding reduced Hen Harrier Circus cyaneus nestlings’ natural food intake by half. Red Grouse Lagopus lagopus scotica chicks constituted 0–4% of all nestling food items. Annually, this reduced annual grouse chick production by 0–6%.

Aim: To quantify proportions of diversionary and natural food (including grouse) delivered to Hen Harrier nestlings in relation to brood size, male status and natural prey abundance.

Methods: We recorded diversionary food provisioned to 25 Hen Harrier broods (2008–15) and studied the diet of 15 broods using observations from hides, nest cameras and regurgitated pellet analysis. Variation in nestling diet was analysed using compositional analysis.

Results: Hen Harriers took 76% of diversionary food provided. Depending on assessment method, average nestling diet was 44–53% diversionary food, 39–55% natural prey (including 24–45% passerines, 4–15% small mammals, 0–4% grouse chicks) and 0–9% unknown items. The amount of diversionary food consumed was not influenced by male status, brood size or natural prey abundance. The number of Red Grouse chicks delivered annually was 34–100% lower than expected under unfed conditions, however, the confidence intervals associated with these estimates were large.

Conclusion: Diversionary food influenced Hen Harrier nestling diet and reduced the number of Red Grouse chicks taken relative to modelled predictions. It may help reduce conflict between Hen Harrier conservation and Red Grouse shooting, but only if overall grouse productivity is thereby maintained or increased.     

Time constraint on food choice in provisioning blue tits, Parus caeruleus: the relationship between feeding rate and prey size

Previous work on food-provisioning behaviour in blue tits suggested that the parents could gather larger prey items only by making longer foraging excursions, for example, by being more selective or by reaching more distant (and less exploited) feeding sites. Here, I show that within-nest, within-day variation in size of prey delivered by the parent could be explained by the time since its last visit. In unmanipulated conditions, size of larvae tended to increase with the time spent away from the nest. A significant positive relationship was more likely at high provisioning rates, suggesting that periods of intense feeding limited the size of prey delivered to the brood. To assess the effect of less intense feeding on prey size, I experimentally increased food availability to the tits. The parents could decide whether to eat the extra food or feed it to the nestlings. In both cases, food supplementation could result in longer time lags between natural feedings. Food-supplemented parents consumed the extra food and fed it to their nestlings, made longer foraging trips and delivered larger natural larvae than controls. In this group, size of larvae was more constant during the observation period and was independent of the time since the parent's last visit. This suggests that, below some value of visit rate, prey size is no longer limited by the duration of the foraging trip. The results support the view that tits continually vary visit rate and prey size. There is some evidence that these adjustments are made by changing food selectivity in response to changes in the state of the brood and of the parents.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

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.     

Biparental care: short-term manipulation of partner contribution and brood size in the starling, Sturnus vulgaris

In species with biparental care, the evolutionarily stable investmentstrategy depends, among other factors, on the reproductive valueof the brood and on the contribution of one's partner. A shortfallin work rate by one parent should be partially compensated forby its partner, while both parents should invest more effortwhen there are more young. We simultaneously tested these predictionsby attaching weights to one member of pairs of European starlings(Sturnus vulgaris), thus reducing one partner's nest visitationrate, and by daily manipulation of brood sizes (between threeand seven chicks). Both sexes compensated to an equivalent degreefor their partner's lower work rate, while at the same timeadjusting flexibly to the daily brood size changes by increasingvisit rates to larger broods. However, this ability to compensatewas limited in the larger brood sizes, perhaps due to an upperlimit on provisioning rate. Weighted birds and their partnersshowed differences in prey types delivered, relative to controls,taking a lower proportion of leatherjackets. With regard tothe proximate cues affecting parental provisioning rate, beggingnoise levels (automatically recorded by computer from microphonesin the nest-box) increased with brood size, but average lengthof begging bout did not. As expected, visit rates per chickdecreased as brood size increased, and this was reflected inlower weight gains per day by chicks in larger broods. Theseresults agree in general with games theory models but revealimportant departures from our previous work with respect to(1) parents reaching an apparent ceiling to nest visitationrate at high brood sizes and (2) the ability to track thesebrood demands with short-term adjustments.     

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

The behavior of young songbirds after fledging is one of the least understood phases of the breeding cycle, although parental provisioning rates and movement of fledglings are key to understanding life history evolution. We studied Cordilleran Flycatchers (Empidonax occidentalis) at two sites in southwestern Colorado, USA, from 2012 to 2017. We banded and sexed breeding adults to determine the relative contributions of males and females to nestling and fledgling care, and attached radio‐transmitters to nestlings to facilitate observations of brood behavior after fledging. Females made 60% and 78% of total observed feedings of nestlings and fledglings, respectively. Parental provisioning rates increased with nestling age, and per‐nestling provisioning rates increased with brood size. Parental provisioning rates declined just before fledging, then increased just after fledging. Fledging times of individuals in broods were asynchronous and concentrated during the late afternoon and early evening. Males stopped caring for fledglings before females even though this species is single‐brooded, with some late‐season broods being abandoned by males. Broods spent the first three weeks after fledging within 400 m of nests, after which they began to disperse. Most aspects of the breeding biology of Cordilleran Flycatchers in our study, including the duration of nestling and fledging periods, female‐dominated provisioning, and movement patterns of fledglings, were similar to those of other Empidonax species. However, the times when young fledged were not concentrated in the morning as reported in most other songbirds, and this result warrants additional study of the timing of fledging in ecologically and taxonomically similar species. The increased per‐nestling provisioning rate with increasing brood size was unexpected, and additional study is needed to determine if this increase results from a trade‐off between adult annual survival and productivity favoring increased provisioning of young in larger broods, or from the existence of high‐quality individuals where larger clutches and higher provisioning rates are linked.     

Provisioning behaviour at the nest in single-parent versus biparental nests and male versus female parents in the common redstart (<Emphasis Type="Italic">Phoenicurus phoenicurus</Emphasis>)

We analysed video-sequences of undisturbed parental provisioning behaviour on 12 nests of common redstart (Phoenicurus phoenicurus). In 4 of the 12 nests, chicks were fed by a single parent only. We compared provisioning rate of chicks, time spent on the nest and food allocation rules between nests with uniparental and biparental care and between male and female parents in biparental nests. In nests with a single parent, the frequency of feeding visits per parent was higher than in biparental nests. As a result, the rate of food provisioning of chicks was similar in uniparental and biparental nests. The food allocation rules did not differ between uniparental and biparental nests. In biparental nests, male and female provisioning behaviour was similar though with two exceptions: males had a strong preference for feeding chicks in front positions in the nest and females spent a longer time on the nest after feeding. We conclude that single common redstart parents are able to compensate fully for the absence of the other parent through increased provisioning efforts, and that in biparental nests, males and females contribute equally to the provisioning of the young.     

Parental behaviour in the Lapwing Vanellus vanellus

Parental behaviour of monogamous and polygynous Lapwings was studied during incubation and brood care. Both parents attended the nest in 86% of monogamous pairs ( n = 29 pairs). In 14% of pairs, only the male parent continued incubation until the eggs hatched, whereas the female deserted the clutch before or at the end of incubation. There was a clear division of parental roles during incubation. Females spent more time incubating (64% of time) than their mates (27%), whereas males spent more time defending the nest (3%) than females (>1%). Time spent incubating did not differ between monogamous and polygynous males. However, polygynous females spent more time incubating (primary females: 95%; secondary females: 97%) than monogamous females. Biparental care was the most common pattern of post-hatching care, although in some broods either the male or the female parent deserted before the chicks fledged. Division of sex roles was less pronounced in brood care than during incubation. Females spent more time brooding (21%) than males (3%), and females attended their chicks more closely than males. Nevertheless, males and females spent similar amounts of time defending the brood from predators and conspecifics. We suggest that the apparent division of parental roles may be explained by sexual selection, i.e. the remating opportunities for male Lapwings might be reduced if they increase their share in incubation. However, the different efficiency of care provision, for example in ability to defend offspring, may also influence the roles of the sexes in parental care.     

Maternal provisioning and possible joint breeding in the burrower bug Adomerus triguttulus (Heteroptera: Cydnidae)

Subsocial burrower bugs (Heteroptera: Cydnidae) provide unique opportunities to investigate evolutionary ecological questions regarding parental provisioning and family dynamics. Observations and marked nutlet‐setting experiments in the field showed that Adomerus triguttulus females progressively delivered mint nutlets into nests harbouring nymphs under the litter. More than one female often attended nymphs, but not eggs, in a nest in the field. The number of nymphs aggregating in a nest with a single female was usually smaller than that in a nest with two females, suggesting the joining of different families and facultative joint parental care. There was a positive correlation between the number of nutlets delivered and the number of nymphs in a nest. The number of attendant females also affected the amount of provisioning; more nutlets were found for second‐instar broods with more females. The effect of brood size on provisioning was confirmed for families under laboratory rearing. Maternal provisioning also varied with the developmental stage of offspring; second‐instar broods received more nutlets than first‐instar broods, with a temporal decrease in provisioning during the moulting of nymphs. Considering the growing evidence of food solicitation signals of young in subsocial insects, the observed finely tuned supply of food by the female could be induced by begging signals from the nymphs.     

Brood size manipulations in Great Horned Owls Bubo virginianus: are predators food limited at the peak of prey cycles?

The reproduction of raptors strongly depends on food resources. It is unclear whether predators experience superabundant food during cyclic peaks of prey populations. In order to test this hypothesis, four pairs of Great Horned Owls Bubo virginianus with two young were subjected to brood size manipulations during high densities of cyclic Snowshoe Hare Lepus americanus populations in southwestern Yukon, Canada. Broods older than 35 days were temporarily enlarged by one, and then by two, young. No effects were observed when one owlet was added, but the addition of two young resulted in significant weight losses in manipulated broods. Females with enlarged broods moved farther from their nest sites at night, presumably reflecting increased hunting effort, and also spent less time near the nest during the day. Food additions to enlarged broods returned the parental behaviour to normal. We conclude that these large predators did not experience superabundant food at this stage of the breeding season during a peak in cyclic prey.