Parental Feeding Rates Research Articles

Experimental warming of embryos accelerates metabolism of postnatal songbirds, influences growth, but has no effects on parental feeding and brooding rates

Abstract Here we investigate possible carryover effects of experimentally increased incubation temperatures for postnatal growth, metabolism, and parental care within and among 6 north temperate and one tropical songbird species. Increased temperatures during embryonic development consistently caused higher postnatal resting metabolism compared to control nests, among but not within the 7 species studied. The effects of the experiment on growth were species specific and depended on the morphometric considered. Size before the fledge date was positively correlated with feeding rate, and metabolism was lower in larger broods. Our experiment did not elicit changes in parental food delivery rates or brooding effort during the postnatal stage, and higher brooding effort was associated with nestlings of smaller mass and faster metabolism independently from treatment. Consequently, parental care seemed unlikely to be the cause of the differences in growth rates between treatments. Instead, physiological mechanisms triggered by our heating treatment appear to be responsible for the observed variation in growth. These intrinsic changes unmatched by adjustments in parental effort may contribute to longer-term consequences for individual quality and survival that deserve further attention.

Does bird photography affect nest predation and feeding frequency?

Bird photography is a popular and growing form of ecotourism that contributes to the economic growth of local communities, but its disturbance to bird reproduction remains understudied. We worked in a tropical forest of southern China, which has experienced a sharp increase in the number of photographers in recent years. We compared nests that were photographed and those that were not, in their nest predation and parental feeding rates. Including nests of 42 species, the results demonstrate that the predation rate of nests that were not photographed (incubation stage: 43.3% of 194 nests; nestling stage: 34.5% of 110 nests) was significantly higher than that of photographed ones (incubation: 2.4% of 83 nests; nestling: 11.1% of 81 nests). Among different nest types, open cup nests in shrub and trees were most affected by photography, in both incubation and nestling stages. Of five factors investigated, including three natural factors (nest stage, structure and position), and two anthropogenic factors (photography and distance to forest edge), only photographic disturbance and nest structure had significant effects (open nests had higher predation). The feeding frequency at nests when photographers were present was not strongly different from when they were not present. Human activity therefore had no negative effects on the birds, but showed a positive effect on their nesting success, in terms of reducing nest predation rates. However, there needs to be further assessment of other aspects of nesting (e.g., clutch size, duration of nestlings in nests), and other kinds of stress responses (e.g., hormonal changes), before the total effect of bird photography can be understood.

Autumn–winter breeding by the Spotted Harrier Circus assimilis in southern Victoria

The breeding cycle of a pair of Spotted Harriers Circus assimilis was observed in southern Victoria, at 38°S, in autumn–winter 2017 for 42 hours over 22 days from incubation to the post-fledging period. From hatching on 10 June and fledging on 19 July, laying was inferred to have commenced on c. 8 May. Three chicks fledged from an initial brood of four; the nestling period was 38 days for the first-hatched chick. Rodents dominated a small sample of identified prey during a plague of House Mice Mus musculus. The male prey-delivery rate to the incubating female was 0.32 item/h, whereas during the nestling period the male brought 0.71 item/h and the female 0.11 item/h for a combined effective delivery rate of 0.64 item/h to nestlings. The combined parental feeding rate to new fledglings was 0.65 item/h. Parental behaviour is described. Juveniles were dependent for 6 weeks after fledging.

Do Parental Feeding Rate and Feeding Synchrony Affect Nest Survival in a Songbird?

Nest predation risk is an important factor that may promote the evolution of adaptive parental reproductive strategies in animals. In altricial birds, where parents feed their offspring at the nest for a period of time, parent birds must balance the benefit from increased nest visits and the cost from increased nest predation resulting from their nest visits being detected by predators. Empirical evidence has shown a relationship between parental nest visits and nest predation risks, and parents have been found to be able to reduce the chance of being detected by predators by synchronizing their feeding visits while maintaining feeding rate unchanged. However, it remains poorly understood whether the relationships are universal to all species. We investigated whether nest survival is correlated with parental feeding rate and feeding synchrony in the silver-throated tit (Aegithalos glaucogularis), a songbird endemic to China. We found that parental feeding rate varied by brood size, nestling age and the time during the day, but feeding synchrony was unrelated to the above factors. Moreover, we showed no effect of parental feeding rate or synchrony on nest survival. The failure to find a relationship between parental feeding synchrony and nest survival seems exceptional because it is contrary to findings of previous studies. While there was likely a publication bias regarding previous studies, it is also possible that the evolution of feeding synchrony in different species has different explanations, or the complexity of the predator community and other factors affecting nest survival need to be considered in the analyses.

Risk of predation on offspring reduces parental provisioning, but not flight performance or survival across early life stages

Abstract Developmental responses can help young animals reduce predation risk but can also yield costs to performance and survival in subsequent life stages with major implications for lifetime fitness. Compensatory mechanisms may evolve to offset such costs, but evidence from natural systems is largely lacking. In songbirds, increased nest predation risk should favour reduced provisioning, but also young that fledge (leave their nest) at an earlier age. Both responses can result in fledglings with shorter wings, reduced mobility and decreased survival. Young may compensate for shorter wings developmentally by reallocating resources towards feather development or behaviourally by adjusting flight kinematics or habitat use. However, underfed young may lack the capacity to express these phenotypes due to insufficient resources or an inability to adjust allocation of resources. Using predation risk experiments and 29 years of observational field data, we test whether increased nest predation risk reduces flight performance and survival during the fledgling stage and explore potential mechanisms that might underlie these effects. We show that young from high‐risk nests did not leave the nest earlier on average, but wing growth was slower likely due to observed reductions in parental feeding rates. Wings were shorter in high‐risk nests when fledglings left the nest early. Yet, fledglings from high‐risk nests showed improved flight performance for a given wing length such that flight performance at fledging did not differ between young from high‐risk and low‐risk nests. Young from high‐risk nests may have offset the costs of shorter wings on flight performance by accelerating the emergence of flight feathers from their sheaths to reduce wing porosity, though evidence for this mechanism was mixed. Fledglings from high‐risk nests also selected habitat with denser woody vegetation compared with young from low‐risk nests. Together, these developmental and behavioural responses seem to mitigate the expected effects of increased nest predation risk on fledgling survival. Ultimately, our results show that offspring predation risk can affect parental provisioning and offspring morphology without major implications for performance and survival in subsequent life stages. A free Plain Language Summary can be found within the Supporting Information of this article.

Interspecific Density Influences the Adaptive Significance of Provisioning Coordination Between Breeding Partners

Cooperation between parents in species with biparental care can reduce sexual conflict and increase reproductive success. If parents cooperate in a conditional way- that is, alternate feeding visits to offspring- this should equalize parental investment and may improve nestling growth. Environmental variation, including competition for limited resources, may influence the need for, and benefits of, parental cooperation. We measured the benefits of partner coordination in offspring provisioning behavior among eastern bluebird partners (Sialia sialis) in which the strength of interspecific density varied spatially. Tree swallows (Tachycineta bicolor) are a recent (<40 years) arrival in our study area, are aggressive nestbox competitors with eastern bluebirds, and their density varies across the field site. Nesting among higher densities of tree swallows led to reduced parental feeding rates and reproductive success of bluebirds. Partner alternation, however, did not vary with tree swallow density. Additionally, alternation level and provisioning rate only influenced nestling growth in areas of high swallow density. It may be that the benefits of parental coordination may only be apparent when environmental conditions are poor. This study provides an important new perspective on the resolution of negotiations between breeding partners; environmental variation could influence the benefits of parental cooperation in a wide variety of animals.

Testing predictions of inclusive fitness theory in inbreeding relatives with biparental care.

Inclusive fitness theory predicts that parental care will vary with relatedness between potentially caring parents and offspring, potentially shaping mating system evolution. Systems with extra-pair paternity (EPP), and hence variable parent–brood relatedness, provide valuable opportunities to test this prediction. However, existing theoretical and empirical studies assume that a focal male is either an offspring's father with no inbreeding, or is completely unrelated. We highlight that this simple dichotomy does not hold given reproductive interactions among relatives, complicating the effect of EPP on parent–brood relatedness yet providing new opportunities to test inclusive fitness theory. Accordingly, we tested hierarchical hypotheses relating parental feeding rate to parent–brood relatedness, parent kinship and inbreeding, using song sparrows (Melospiza melodia) experiencing natural variation in relatedness. As predicted, male and female feeding rates increased with relatedness to a dependent brood, even controlling for brood size. Male feeding rate tended to decrease as paternity loss increased, and increased with increasing kinship and hence inbreeding between socially paired mates. We thereby demonstrate that variation in a key component of parental care concurs with subtle predictions from inclusive fitness theory. We additionally highlight that such effects can depend on the underlying social mating system, potentially generating status-specific costs of extra-pair reproduction.

Physiological stress and behavioural responses of European Rollers and Eurasian Scops Owls to human disturbance differ in farming habitats in the south of Spain

SummaryHuman activities are altering ecosystems and threatening the well-being of wildlife. The study of the stressful effects of human disturbances on animal distribution, physiology and behaviour can provide fundamental insights for wildlife conservation. Here, we assess how two declining birds, the European Roller Coracias garrulus and the European Scops Owl Otus scops, cope with alteration by human activities in farming habitats of the south of Spain. We studied nest distribution, quantified nestling physiology (corticosterone levels in plasma and feathers and body weight close to fledgling) and parental behaviour (feeding rates) of both species along a human alteration gradient. Rollers and Scops Owls used the same type of habitat and their spatial distribution was not determined by individual quality. In Rollers, nestlings raised in scrubland areas had high stress-induced corticosterone levels, possibly due to high predation risk in this habitat. In addition, Rollers and Scops Owls showed opposite relationships with farming activity and human disturbance. Nestling Rollers showed the highest corticosterone levels in feathers, weight and parental feeding rates in areas with intense farming activity. These results suggest that despite the disturbance produced by farming activities, inducing a higher stress in these areas, cultivated areas may, simultaneously, provide parents with a higher abundance of prey which would trigger increased feeding rates and, hence, higher nestling weights. Furthermore, nestling Scops Owls showed the highest stress-induced corticosterone levels in areas close to roads, suggesting that they would be affected by human disturbance due to infrastructures that disturb also at night when Scops Owls are active. Therefore, susceptibility to human disturbance may vary between species, probably due to variation in the daily pattern of human activities and the species’ activity rhythm, buffering or exacerbating the effects, which should be considered in future studies on human alterations and birds.

Adult Provisioning Influences Nestling Corticosterone Levels in Florida Scrub Jays (Aphelocoma coerulescens).

We studied Florida scrub jay (Aphelocoma coerulescens) nestlings to examine the relationship between parental feeding rates and levels of corticosterone (CORT), a metabolic and stress-related steroid hormone hypothesized to play a role in mediating begging behavior. It has been documented that nutritional deficiency results in increased glucocorticoid levels in nestling birds. Further, previous studies have found that CORT levels of Florida scrub jay nestlings are negatively correlated with parental nest attendance and provisioning rates; however, the behavioral observations were made several days before the collection of samples to assess CORT levels. Few studies have investigated whether experience immediately before sampling impacts nestling glucocorticoid levels, especially in a free-living species. By monitoring parental activity at the nest before sample collection, we found that nestling CORT levels varied as a function of parental provisioning rate and the time since their last feed. However, counter to our predictions, higher provisioning rates and more recent feedings were associated with higher CORT levels in nestlings rather than lower CORT levels. These results suggest that some aspect of parental provisioning results in increased CORT levels in nestling Florida scrub jays.

Effects of experimental chronic traffic noise exposure on adult and nestling corticosterone levels, and nestling body condition in a free-living bird

Transportation noise affects urbanized, rural, and otherwise unaltered habitats. Given expanding transportation networks, alterations in the acoustic landscapes experienced by animals are likely to be pervasive and persistent (i.e. chronic). It is important to understand if chronic noise exposure alters behavior and physiology in free-living animals, as it may result in long-lasting impacts, such as reduced reproductive success. Here, we experimentally tested the effects of chronic traffic noise on baseline and stress-induced corticosterone (the primary avian glucocorticoid), parental feeding behavior, and fitness proxies in breeding tree swallows (Tachycineta bicolor). Our results show that chronic traffic noise is related to altered corticosterone in both adult female and nestling tree swallows, suggesting that noise may be a stressor in both groups. In adult females, our results suggest that traffic noise is related to a limited ability to respond to subsequent acute stressors (i.e. reduced stress-induced corticosterone levels after handling). Further, our results show no evidence of habituation to noise during the breeding season, as the negative relationship between traffic noise and adult female stress-induced corticosterone became stronger over time. In nestlings, we found a positive relationship between traffic noise exposure and baseline corticosterone. Finally, we found a negative relationship between traffic noise and nestling body condition, despite no detectable effects of noise on nestling provisioning (e.g. parental feeding rate, or insect bolus size/composition). These results highlight the potential long-term consequences of chronic noise exposure, as increased baseline corticosterone and reduced nestling body condition in noise-exposed areas may have negative, population-level consequences.

The Impact of the Female Immune Challenge on Parental Feeding Rate, Mass and Body Condition Index of Offspring

Reproduction is a resource-demanding period, when trade-offs between investment in immunity versus other functions of an adult organism may exist. This research investigates the potential trade-off between a challenged immune system of a female parent and parental provisioning in free-living Great Tits Parus major and Eurasian Blue Tits Cyanistes caeruleus. In both species, half of females were challenged with sheep red blood cells (SRBC) as an antigen, while the others were injected with phosphate buffer saline (PBS) as a control. Six days later – at the day assumed to be the peak of an immune response in birds treated with SRBC, when nestlings were nine days old – parental feeding rates were recorded. Two days later (and eleven days after hatching), nestling mass and body condition index (BCI) were quantified. SRBC challenge of the female increased feeding rates of Great Tit males and females, but did not change parental provisioning in Eurasian Blue Tits. This may be explained by the different reproductive strategies in these two bird species. Parental provisioning influenced the mass and BCI of offspring. In both species, offspring mass was lower and BCI was higher in the SRBC group than those in the control group. This means that high providers, such as Great Tits with increased feeding rates, do not always raise chicks with high fledgling mass. Parental provisioning is one of the key factors linking reproduction and the immune system.

Management-Related Traffic as a Stressor Eliciting Parental Care in a Roadside-Nesting Bird: The European Bee-Eater Merops apiaster.

Traffic is often acknowledged as a threat to biodiversity, but its effects have been mostly studied on roads subjected to high traffic intensity. The impact of lower traffic intensity such as those affecting protected areas is generally neglected, but conservation-oriented activities entailing motorized traffic could paradoxically transform suitable habitats into ecological traps. Here we questioned whether roadside-nesting bee-eaters Merops apiaster perceived low traffic intensity as a stressor eliciting risk-avoidance behaviors (alarm calls and flock flushes) and reducing parental care. Comparisons were established within Doñana National Park (Spain), between birds exposed to either negligible traffic (ca. 0–10 vehicles per day) or low traffic intensity (ca. 10–90 vehicles per day) associated to management and research activities. The frequencies of alarm calls and flock flushes were greater in areas of higher traffic intensity, which resulted in direct mortality at moderate vehicle speeds (≤ 40 km/h). Parental feeding rates paralleled changes in traffic intensity, but contrary to our predictions. Indeed, feeding rates were highest in traffic-exposed nests, during working days and traffic rush-hours. Traffic-avoidance responses were systematic and likely involved costs (energy expenditure and mortality), but vehicle transit positively influenced the reproductive performance of bee-eaters through an increase of nestling feeding rates. Because the expected outcome of traffic on individual performance can be opposed when responses are monitored during mating (i.e. negative effect by increase of alarm calls and flock flushes) or nestling-feeding period (i.e. at least short-term positive effect by increase of nestling feeding rates), caution should be taken before inferring fitness consequences only from isolated behaviors or specific life history stages.

Nestling Growth is Impaired by Heat Stress: an Experimental Study in a Mediterranean Great Tit Population.

Samuel Rodríguez and Emilio Barba (2016) During the nestling stage, nestlings of small altricial birds face energetic limitations due to their rapid development and the need to maintain a stable body temperature once homeothermy is achieved. In Mediterranean habitats, high air temperatures reached during the breeding season could negatively affect the health and condition of the nestlings. The aim of this study was to determine the effect of an experimental increase of nest temperatures during the nestling stage on the growth and survival of Great Tit (Parus major) nestlings. Additionally, changes in parental brooding and feeding behavior as a result of the alteration of the nest microclimate were addressed. Increased nest temperatures affected nestling mass, as heated nestlings were lighter than controls on day 15 in the warmer of the two breeding seasons considered. Moreover, females from the heating treatment reduced their brooding time. Fledging success and parental feeding rates were not altered by the experimental treatment. The results of this study suggest that high nest temperatures may impair nestling development and therefore affect post-fledging survival probability. Negative effects are more likely to occur in warm habitats and/or warmer years, where juveniles are liable to suffer from thermal stress.

Biparental behavior in the burying beetleNicrophorus orbicollis: a role for dopamine?

Burying beetles Nicrophorus orbicollis exhibit facultative biparental care of young. To reproduce, a male–female burying beetle pair bury and prepare a small vertebrate carcass as food for its altricial young. During a breeding bout, male and female behavior changes synchronously at appropriate times and is coordinated to provide effective care for offspring. Although the ecological and evolutionary factors that shape this remarkable reproductive plasticity are well characterized, the neuromodulation of parental behavior is poorly understood. Juvenile hormone levels rise dramatically at the time beetle parents accept and feed larvae, remain highly elevated during the stages of most active care and fall abruptly when care is terminated. However, hormonal fluctuations alone cannot account for this elaborate control of reproduction. The biogenic amines octopamine (OA), dopamine (DA), and serotonin (5-HT) mediate a diversity of insect reproductive and social behaviors. In this study, we measured whole brain monoamine levels in individual male and female burying beetles and compared OA, DA, and 5-HT profiles between breeding (parental) and nonbreeding, unmated beetles. Remarkably, after 24 h of care, when parental feeding rates begin to peak, DA brain levels increase in breeding beetles when compared to nonbreeding controls. In contrast, brain OA and 5-HT levels did not change significantly. These results provide the first evidence for a potential role of DA in the modulation of burying beetle parental behavior.

Baseline innate immunity does not affect the response to an immune challenge in female great tits (Parus major)

The immune system is an important defence against pathogens but requires resources that hosts may also use otherwise. Thus, trade-offs between investment in immunity versus other life-history traits may exist, especially during resource-demanding periods such as reproduction. Here, we investigated the potential trade-off between an activated immune system and parental care in free-living great tits. We also studied whether variation in baseline immune indices prior to immunization contributes to individual differences in the responses to an immune challenge. To this end, we injected free-living great tit females with either phosphate-buffered saline (PBS) or with bacterial lipopolysaccharides (LPS) when nestlings were 9 days old and subsequently recorded parental feeding rates. We quantified potential fitness consequences via the growth and survival of their nestlings. Exposure to LPS tended to decrease female feeding rates. However, nestling body mass was not affected by the maternal immune challenge, probably because males compensated for the change in feeding rate of their partner. We found a negative relationship between haptoglobin levels and female feeding rates pre-treatment, but not with any of the other innate immune traits. Although there was substantial variation in female innate immune indices, we found no evidence that baseline immunity affected how females reacted to an immune challenge in terms of changes in parental behaviour.

Effects of increased begging and vitamin E supplements on oxidative stress and fledging probability

The evolution of conspicuous begging displays has been suggested as the outcome of a conflict where offspring attempt to manipulate food allocation beyond the parental optimum. One resolution for the conflict arises via costs of begging, and oxidative stress has been proposed as a major mechanism for causing begging-induced costs. Although begging can be a physically demanding activity, the evidence for causing oxidative stress is scarce. Great tit (Parus major) parents provide food at the nest mostly from 2 different locations, which in consequence relaxes nestling competition. Here, we manipulated nestling competition by forcing parents to feed from a single location and supplemented half of the nestlings in each brood with vitamin E to test if this major antioxidant can alleviate a potential oxidative cost of begging. The design increases the cost of begging without altering parental feeding rates. Begging intensity was significantly higher when parents fed from a single location. Body mass and antioxidant capacity were not affected by the increase in begging, but oxidative damage was lower in females of the increased begging group compared with those in the control group, independent of vitamin E supplementation. The results suggest that oxidative stress is rather a minor cost of begging. Vitamin E–supplemented nestlings had a higher probability to fledge, which underlines the important role of vitamin E during development, although this might not be due to its role as an antioxidant.

The alarm call system of breeding Brown Thornbills (Acanthiza pusilla): self-defence or nest defence?

Many species produce alarm calls during predator encounters that are directed at either conspecifics or the predator. Although many studies have investigated alarm calls in foraging individuals, antipredator communication during reproduction is rarely studied. In birds, where nest predation is a key cause of reproductive failure, some species have evolved sophisticated alarm calls to inform nestlings of danger from nest predators. However, different predator species differ in their primary prey type (brood predators, predators of adults), and accordingly, birds could have evolved different alarm calls depending on who is in danger. We experimentally investigated parental antipredator communication in Brown Thornbills (Acanthiza pusilla), where more than 50 % of all nests are depredated. We presented breeding pairs the models of a brood predator, a predator of adult birds and a harmless control species. Parents gave two different alarm calls (short and intense tzzt calls), which were not predator-specific, but responded to the predator of adults with more alarm calls than for the brood predator. Parental alarm calls did not affect nestling begging levels, which were influenced only by parental feeding rate. Our results suggest that alarm calls of breeding Brown Thornbills are mainly used as a form of self-defence by the individuals of the breeding pair rather than being directed at the nestlings. This fits with the predictions of life-history theory that parents in long-lived species are more concerned about their own survival.

Coadaptation of Offspring Begging and Parental Provisioning - An Evolutionary Ecological Perspective on Avian Family Life

Offspring begging and parental provisioning are the two central social behaviours expressed during the period of parental care. Both behaviours influence each other and it is, therefore, hypothesized that they should ultimately become (genetically) correlated, stabilized by fitness costs to parents and/or offspring. By reciprocally exchanging entire clutches in canaries (Serinus canaria), we tested (1) whether there is covariation between these behaviours and (2) whether a mismatch - as introduced by cross-fostering - entails costs. Begging was scored in a standardized begging test and parental provisioning was measured via (a) the actual feeding rate and (b) using the growth rate of the foster nestlings as a proxy. Costs were established in terms of future reproductive investment in subsequent clutches and offspring growth. We found a positive and significant phenotypic covariation between offspring begging and parental feeding when using the growth rate as a proxy and, to a lesser extent, in case of the parental feeding rate. Female parents suffered no future reproductive costs when feeding foster nestlings that were more demanding than their own nestlings. Neither growth measured amongst all offspring nor the reproductive investment measured amongst the female offspring as adults was influenced by their begging behaviour. However, the reproductive investment of female offspring tended to depend on the parental qualities of their foster parents. Thus, offspring may only be able to extract resources within the limit of generosity of their foster parents. This suggests parental control of feeding, which is also supported by the positive covariation between offspring begging and parental feeding.

The relationship between maternal ornamentation and feeding rate is explained by intrinsic nestling quality

In altricial birds, parental feeding is essential, and its amount may depend on the quality of both parents. A relationship between parental quality and feeding rate is generally attributed to an active adjustment by parents in order to retain good quality mates or ensure high fitness through raising high-quality offspring. However, the behaviour and need of young may also change with parental quality, and this may affect parental behaviour. A further problem is that most studies have investigated post-hatching parental investment in relation to the secondary sexual signals of males, but not females. In a cross-fostering experiment, we examined the feeding rates of rearing parents in relation to the size and ornamentation of both original and rearing parents in collared flycatchers (Ficedula albicollis). Using this setup, we could examine whether the observed feeding patterns were the results of the decision of the parents based on their own and their partner’s traits or the constraints imposed by the behaviour or need of offspring. When correcting for clutch size and year, we found that feeding rate of both foster parents correlated with the wing patch size of the original female. This implies that original maternal quality had an offspring-mediated indirect effect on investment of foster parents, that is intrinsic nestling quality may constrain parental feeding decisions. This explanation should not be overlooked in future studies on preferential parental investment, and our results also point out that maternal ornaments deserve more attention in such studies.

Intensity of mouth coloration in Blackcap Sylvia atricapilla nestlings affects food distribution among siblings but not provisioning of the whole brood

Among various begging stimuli, mouth coloration has received increasing attention in recent years, and previous research has demonstrated that mouths of nestling Canaries Serinus canaria get redder with the extent of food deprivation and that parents preferentially feed nestlings of redder gapes. This study assesses whether the intensity of red mouth colour in nestling Blackcaps Sylvia atricapilla is a signal in parent–offspring communication. This is one of the few species with a naturally red gape in which the function of mouth redness has been tested. Three predictions were experimentally tested: (1) reddening the gape of a single nestling within a brood increases its provisioning in relation to other siblings; (2) reddening the gapes of all nestlings within a brood increases parental feeding rate; and (3) food deprivation increases nestling mouth redness. The effect of nestling quality on mouth redness was also assessed. The intensity of gape coloration affected food distribution, but in a way opposite to that expected: an increase in mouth redness of the nestling caused reduced feeding by parents. However, reddening the gapes of all nestlings had no effect on provisioning of the whole brood, suggesting that Blackcap parents use different cues for provisioning particular nestlings and the whole brood. Intensity of mouth redness in Blackcap nestlings was not affected either by food deprivation or by nestling quality in terms of mass and rank in the nest.