Nestling Mass Research Articles

Relative influence of male and female care in determining nestling mass in a migratory songbird

Biparental care is common in birds, with the allocation of effort being highly variable between the sexes. In most songbird species, the female typically provides the most care early in the breeding cycle with both parents providing care when provisioning young. Food provisioning should be directly related to offspring quality; however, the relative influence each parent has on offspring quality has rarely been assessed at the nest level. Consequently, we were interested in assessing the relative influence male and female provisioning has on one measurement of offspring quality, nestling mass, in the black‐throated blue warbler Dendroica caerulescens. Over a six year period, 2003–2008, we collected information on average nestling mass per brood on day 6 of the nestling cycle and parental provisioning rates on day 7 of the nestling cycle from 182 first brood nests on three different study plots. We found that average nestling mass was directly related to male provisioning rate, while it was not related to female provisioning rate. On the other hand, estimated biomass provisioned had little influence on average nestling mass, calling into question its utility in assessing parental quality. Finally, there was some indication that parental influence on average nestling mass was dependent on the other parent's provisioning rate, suggesting that parents work in concert to influence nestling quality.

Egg size and asymmetric sibling rivalry in red-winged blackbirds

How big to make an egg is a life history decision that in birds is made coincident with a series of other similar decisions (how many eggs to have, whether to fortify them with maternally derived hormones or immune system boosters, whether to hatch the eggs synchronously or asynchronously). Though within-population variation in egg size in birds has been well studied, its adaptive significance, if any, is unclear. Here we examine within-population variation in egg size in relation to asymmetric sibling rivalry in a 17-year study of red-winged blackbirds (Agelaius phoeniceus), an altricial songbird. Egg mass showed a twofold range of variation, with roughly 80% of the variation occurring across clutches. By commencing incubation before the clutch is complete, mothers create advantaged core and disadvantaged marginal elements within their brood. Previous work on this system has shown that sibling competition is asymmetric, and that core offspring enjoy priority access to food, and as a consequence show higher growth and lower mortality than marginal offspring. Here we examine the effect of initial egg size on nestling growth and survival in relation to these competitive asymmetries. Egg mass was strongly linked to hatchling mass, and remained significantly related to the mass of both core and marginal nestlings; the effect of egg size was stronger for core offspring early in the nestling period, but the disparity between core and marginal nestlings narrowed as they approached fledging age, and slower growing marginals fell victim to brood reduction. The effect of egg mass on survival differed dramatically between core and marginal nestlings. Egg mass was significantly related to the survival of marginal but not core nestlings: below average egg mass was associated primarily with very early mortality. Asymmetric sibling competition is clearly a strong determinant of the consequences of egg size variation.

Fledging Success is a Poor Indicator of the Effects of Bird Blow Flies on Ovenbird Survival

Abstract. Infestations of bird blow flies (Protocalliphora spp. and Trypocalliphora braueri) have various negative effects on the condition of nestling birds. In the absence of other stressors such as inclement weather, however, infestation alone rarely reduces fledging success. Previous studies have documented effects of blow flies on nestling condition and fledging success. Without information regarding fledgling survival, the full effect of blow-fly infestation remains unclear. To fully investigate the effect of blow-fly infestation on reproductive success of the Ovenbird (Seiurus aurocapilla), we monitored infested and non-infested nests and monitored fledglings from each by using radio telemetry. Blow flies did not affect birds during the nestling period, as brood size, mean nestling mass, fledging success, and time to fledging in infested and non-infested nests were no different. Fledgling survival and minimum distance traveled the first day after fledging, however, were significantly lower for infe...

Parental provisioning and offspring fitness: size matters

Parental food deliveries are generally assumed to promote offspring fitness in altricial birds, mainly because mass at fledging often predicts recruitment as breeding adults. We studied how such provisioning influences recruitment in house sparrows, Passer domesticus, through both a traditional two-step indirect analysis (via fledging mass) and a single direct analysis. In our study, total parental deliveries predicted neither fledging mass nor recruitment. Instead, delivery of the largest food items (‘e-prey’) predicted both. Offspring recruitment was determined only by personal mass, but from a parental perspective, the number of recruits per brood hinged principally on two factors, brood size and mean nestling mass at fledging. As in other species, recruitment probability declined across the breeding season, even though deliveries of the largest food items increased. Within the natural range of provisioning that parents achieved, the function relating e-prey and recruitment appeared to be accelerating, indicating that parents could rapidly enhance offspring success if bringing more of those items were possible. The failure of adults to do so suggests that the associated foraging costs are likely to be prohibitive, illustrating what has been called a ‘food ESS’ for parental care.

Glucocorticoid response to food availability in breeding barn swallows ( Hirundo rustica)

Parents feeding altricial nestlings have to trade-off the competing demands of self-maintenance and reproductive investment over their lifetime. Corticosterone, a glucocorticoid hormone released by birds in response to stressors, might play a key role in regulating parental investment when conditions unexpectedly deteriorate. However, birds breeding in unpredictable environmental conditions have been shown not to increase circulating levels of corticosterone as a response to bad weather to avoid nest abandonment when investment in offspring is high or when the probability of re-nesting is low. We investigated whether parent barn swallows Hirundo rustica, a passerine bird whose aerial insect food varies greatly in abundance depending on weather, also belongs to those species or whether it responds with an activation of the hypothalamo-pituitary-adrenal axis to natural variation in insect availability. We correlated plasma corticosterone levels of parents with weather conditions, the availability of aerial insects and parental body condition. Plasma corticosterone concentrations increased when mean daytime temperature declined, and consequently insect availability decreased and body condition of the parents deteriorated. Low temperatures also had a negative effect on body mass of the nestlings and there was a negative relationship between circulating corticosterone of parents and body mass of nestlings. We conclude that corticosterone is probably involved in the regulation of parental investment.

Predation risk is unlikely to account for the failure of subordinate speckled warblersChthonicola sagittatato help at the nest

The predator avoidance hypothesis suggests that the failure of subordinate birds to provision nestlings in communally breeding species is a consequence of increased predation risk. Parents exclude subordinates from the nest area and thus reduce the frequency of predator‐attracting visits when the nest is most vulnerable, leading to increased reproductive success. I evaluated this hypothesis for the speckled warblerChthonicola sagittata, a group‐living member of the Pardalotidae in which subordinate males never feed nestlings or fledglings even though they are unrelated to the primary pair, compete for copulations and sometimes sire young in the brood. Parents did not modify provisioning behaviour relative to the risk of nest predation; provisioning rates to 10 d‐old nestlings were similar on high and low risk territories. Furthermore, there was no evidence that parents modified the timing of deliveries or adjusted the relative size of deliveries in relation to predation risk. The condition (residual mass) of nestlings differed between high and low risk territories because nestlings on high risk territories had smaller tarsi but similar body mass to those at low risk. Tarsus length was the result of parental phenotype, not modified provisioning behaviour. Given that parents were unresponsive to predation risk, it seems unlikely that predation can account for the failure of subordinates to provision at the nest.

Carotenoid availability does not limit the capability of nestling kestrels (Falco tinnunculus) to cope with oxidative stress

It is recognized that carotenoids are useful anti-oxidants in embryo and hatchling avian models. However, recent evidence suggests that the anti-oxidant role of carotenoids in nestling or adult birds may not be as important as previously thought. The aim of the present work was to investigate if supplemental carotenoids decreased the level of oxidative damage (by reactive oxygen metabolites, ROMs) and increased the serum anti-oxidant capacity (OXY) in nestling Eurasian kestrels Falco tinnunculus. Circulating carotenoids in supplemented nestlings increased about 1.5-fold compared to the control and pre-treatment levels at the end of the supplementation period. There was no effect on ROMs, OXY or the level of oxidative stress (ratio between ROMs and OXY), however, or on body mass or body condition of nestlings. ROMs and OXY decreased with age, but this pattern varied across the nests. Our results show that (i) in general, younger nestlings actually have to cope with a high free radical production, and (ii) the ability of wild nestling kestrels to cope with oxidative stress is not affected by carotenoid availability.

Experimental addition of greenery reduces flea loads in nests of a non‐greenery using species, the tree swallowTachycineta bicolor

Several bird species, including cavity‐nesters such as European starlingsSturnus vulgaris, add to their nests green sprigs of plants such as yarrowAchillea millefoliumthat are rich in volatile compounds. In this field study on another cavity‐nester, tree swallowsTachycineta bicolor, we tested whether yarrow reduced ectoparasite loads (the nest protection hypothesis), stimulated nestling immune systems (the drug hypothesis), or had other consequences for nestling growth or parental reproductive success (predicted by both preceding hypotheses). Tree swallows do not naturally add greenery to their nests, and thus offer several advantages in testing for effects of greenery independent of other potentially confounding explanations for the behaviour. We placed fresh yarrow in 23 swallow nests on the day the first egg was laid, replenishing every two days until clutch completion (=three times), and at 44 control nests, nesting material was simply touched. At 12 days of age, we measured nestling body size and mass, and took blood smears to do differential white blood cell counts. We subsequently determined the number and proportion of young fledging from nests and the number of fleas remaining after fledging. Higher humidity was associated with higher flea numbers whereas number of feathers in the nest was not. Our most significant finding was that an average of 773 fleasCeratophyllus idiuswas found in control nests, versus 419 in yarrow nests. Possibly, parents compensate for blood that nestlings lose to ectoparasites by increasing food delivery, because we detected no differences between treatments in nestling mass, nestling leukocyte profiles, or proportion of young fledging, or relative to flea numbers. Our results provide no support for the drug hypothesis and strong support for the nest protection hypothesis.

Impacts of roads associated with the Ekati Diamond MineTM, Northwest Territories, Canada, on reproductive success and breeding habitat of Lapland Longspurs

We examined the effects of roads associated with the Ekati Diamond MineTM, Nortwest Territories, Canada, on reproductive success and breeding habitat of Lapland Longspurs (Calcarius lapponicus (L., 1758)) by comparing these attributes on study sites located directly beside and at least 5 km away from roads. No significant differences between roads and reference sites were detected for first-egg dates, clutch size, mean nestling mass on the 7th day following hatch, or daily nest survival. We found no evidence that Lapland Longspurs were avoiding nest sites located near roads. Recorded frequencies of male song overlapped with the harmonics of heavy-truck noise. Snow-water equivalent and percent cover of mosses were significantly higher on reference sites, while soil moisture and dust deposition were higher on road sites. Dust suppressant applied midway through the breeding season significantly reduced dust deposition. Lapland Longspur nest sites had significantly higher percent cover of graminoids and of shrubs and forbs, and significantly lower percent cover of lichens than random sites, an effect that occurred both near and distant from roads. Currently, there appears to be no measurable effect of roads associated with the Ekati Diamond MineTM on current territorial choice and reproductive performance of Lapland Longspurs. Observed differences in habitat characteristics between reference plots and road plots suggest that long-term changes in the vegetation community may occur that could affect nest-site selection of Lapland Longspurs.

Individual quality mediates trade‐offs between reproductive effort and immune function in tree swallows

Summary Individual variation in the trade‐off between self‐maintenance and offspring quality was assessed in tree swallows, Tachycineta bicolor, by manipulating reproductive effort while simultaneously immunochallenging breeding females. An experimental manipulation of parental effort was conducted by creating broods of, on average, three, five and eight nestlings. Breeding females were immunochallenged to mount a humoral immune response to sheep red blood cells (SRBC) and a cell‐mediated response to phytohaemagglutinin (PHA). The consequences of adult decisions on offspring quality were assessed through immune responses to PHA, growth rates and residual body mass of nestlings. Clutch initiation date, a strong measure of individual quality in tree swallows, was linked with immune responses, with earlier‐nesting, presumably higher quality, females mounting stronger immune responses than did later‐nesting birds. Increased reproductive effort led to decreased parental immune responses. There was a significant interaction between individual quality and reproductive effort treatment, with lower‐quality individuals showing greater depression of humoral immune response to SRBC while raising enlarged broods, suggesting individual‐level variation in trade‐offs. Breeding females raising enlarged broods tended to raise offspring of similar quality to control females, with only growth rate decreasing with increasing brood size, but not residual nestling body mass or nestling immunocompetence. This suggests that females are maintaining offspring quality at the cost of their own immune system maintenance.

Colony size, reproductive success, and colony choice in Cave Swallows Petrochelidon fulva

We investigated how annual reproductive success, as measured by the number of nestlings surviving to day 10 and the percentage of nests that were successful, varied with colony size of the Cave Swallow Petrochelidon fulva in south central Texas. We also studied whether Cave Swallows chose colonies, in part, on the basis of reproductive success at a site the previous year. Neither measure of reproductive success varied significantly with colony size for either first‐wave or second‐wave nestings. Mean clutch size per colony did not vary significantly with colony size. Mean nestling body mass, an index of parental foraging efficiency, was unrelated to colony size, except for broods of five, in which nestling mass declined significantly with colony size. Colony size was not significantly affected by reproductive success at the site the previous year, although sites with more successful nests during the first wave declined less in size during the second wave within the same season than did sites that had fewer successful first‐wave nests. Unlike the closely related Cliff Swallow Petrochelidon pyrrhonota, Cave Swallows did not use breeding performance of conspecifics in choosing nest‐sites, because they did not preferentially aggregate at sites that were the most successful the previous year. Coloniality in Cave Swallows did not appear to have a net negative effect on annual fitness, suggesting that colonial nesting was not solely a response to nest‐site limitation, but the benefits of breeding colonially (if any) were unclear.

The Effect of Egg Size on Growth and Survival of the Tree SparrowPasser montanusNestlings

The paper analyses the effect of egg dimensions (volume, breadth, and length) on the growth and development of Tree Sparrow nestlings on successive days of life. Egg size did not influence nestling mortality. It was found that for most days of nestling life, the mean volume and breadth of eggs were positively correlated with the mean mass of nestlings in the nest. Similarly, the deviation of the volume and breadth of a particular egg from the mean egg volume and breadth in the clutch was positively correlated with the deviation of nestling mass from the mean nestling mass in the nest. Nestling growth and development in terms of asymptotic mass (g), maximum growth rate (g/day), tarsus length, and longest remex length were also positively correlated with egg size. The effect of egg size was particularly pronounced in the period of termination of intensive growth rate, development of thermoregulation, and feather development. It is possible that larger eggs contain more microelements, hormones, antioxidants, and vitamins.

Detrimental effects of larval blow flies (Protocalliphora azurea) on nestlings and breeding success of Tree Sparrows (Passer montanus)

The effect of bloodsucking parasitic larvae of the blow fly Protocalliphora azurea (Fallén, 1817) (Diptera) on Tree Sparrow, Passer montanus (L., 1758), breeding success was studied in populations breeding in nest boxes in southwestern Slovakia. Out of 52 examined nests only seven broods (13%) were unparasitized. The mean number of larvae per parasitized nest was 22.6 and the total number of parasites per nest ranged from 1 to 80. Large numbers of blow fly larvae and pupae significantly influenced nestling survival and fledging success. In broods with parasite load per chick higher than nine, at least one nestling died. To record the effects of parasites on the body size of nestlings of different ages, nestlings were measured on days 5, 10, and 13 post hatch. First and second broods were analysed separately. A significant negative effect of parasite load per nestling on the body mass, wing length, tarsal length, and tail length of nestlings was found in the second broods only in the 10- and 13-day-old chicks. Tree Sparrow parents did not prolong nestling provisioning time per nestling, as there was no negative relationship between parasite load per nestling and feeding period. Contradictory to most previous studies of the genus Protocalliphora, the present study suggests that these parasites have an important negative impact on the breeding success of the studied Tree Sparrow populations.

Helpers increase long-term but not short-term productivity in cooperatively breeding long-tailed tits

Helpers at the nest in the cooperative breeding system of long-tailed tits Aegithalos caudatus exhibit kin preference in their helping behavior. The aim of this study was to use multivariate analyses to investigate whether helpers accrue indirect fitness benefits through their cooperation by increasing the productivity of relatives. All birds started each season breeding independently in pairs, but birds that failed in their own breeding attempt often redirected their care to help another pair provision their offspring. About half of all broods had one or more helpers, 86% of which were male. Provisioning rates increased and there was a corresponding increase in the mass of nestlings within broods as the number of helpers increased. Helpers had no significant short-term effect on productivity because nest predation, nestling survival, and brood size were unaffected by the presence of helpers. However, in the long term helpers had a highly significant effect on the recruitment of fledglings, the positive effect of helpers being linear within the range of helper numbers that we observed. We found no evidence to suggest that these results were confounded by the effects of individual or habitat quality. We conclude that long-tailed tits accrue indirect fitness benefits by helping kin. Nevertheless, the inclusive fitness benefit from helping is substantially lower than that of independent breeding, showing that helpers are making the best of a bad job.

Multiple effects of brood parasitism reduce the reproductive success of prothonotary warblers, Protonotaria citrea

Avian brood parasitism often has multiple negative effects on the reproductive success of the host. Most studies have focused on one or two of these effects, but rarely have they all been studied simultaneously for one species. I studied prothonotary warblers to quantify the effects of different intensities of (i.e. multiple) brood parasitism by brown-headed cowbirds, Molothrus ater, on the production of host and cowbird young and on the between-year returns of adult warblers. Host clutch size decreased with an increase in the number of cowbird eggs laid in nests. The hatching success of warbler and cowbird eggs decreased with increased cowbird eggs in nests, but was always higher for cowbird eggs than warbler eggs. The survival of warbler nestlings, but not cowbird nestlings, decreased with increased cowbird nestlings in the brood. An increase in the number of cowbird nestlings in broods resulted in a reduction in the average mass of warbler nestlings but not cowbird nestlings. The number of cowbird eggs or nestlings present did not affect nest predation, and the fledging of cowbirds did not influence the renesting interval of female warblers. In addition, the between-year returns of adult warblers were not negatively affected by brood parasitism. Decreased hatching success and nestling survival reduced the reproductive output of the warblers the most. These effects were substantial and appear to favour the evolution of behavioural responses that reduce the effects of brood parasitism on prothonotary warblers. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour

Different effects of age on reproductive performance in relation to breeding stage in Bull-headed Shrikes

The difference in the reproductive performance of males and females of the Bull-headed Shrike (Lanius bucephalus) according to age class, i.e. yearling and adult, was studied, and the age-related difference was examined according to parental feeding behavior. The clutch initiation date was not affected by the age class. Females that paired with an adult male laid more eggs per clutch than those paired with a yearling male. The age class of males affected the mass of nestlings at 6 days old, and the age class of females affected the mass of nestlings at 12 days old. The effects of the age of either parent independently were observed at different breeding stages. A change in the degree of nestling feeding peformed by the male and female parents occurred at some point between when the broods were 6 days and 12 days old. It is likely that this caused an effect of age at different stages of the breeding cycle. The effects of the age of the male parent are consistent with accounts of age-related reproduction in raptors where males provide resources to offspring. Individual improvements in foraging skills and/or courtship feeding rate are suggested to be possible explanations.

Prudent investment in rearing nestlings in bull‐headed shrikes

I investigated seasonal changes in the relationships between brood size, body mass of nestlings and body mass of parents of the bull‐headed shrike, Lanius bucephalus, in Ishikari, northern Japan. When the broods were 12 days old, the body mass of the heaviest nestling in a brood did not differ among brood sizes, or throughout the season. However, the body mass of the lightest nestlings in a brood was different among brood sizes. The body mass of the lightest nestling in five‐ and six‐nestling broods decreased throughout the season. The lightest nestling in four‐nestling broods, and the lightest and the second lightest nestlings in five‐nestling broods, were significantly lighter than the heaviest nestling in broods of this size. It is likely that pairs with six nestlings at 12 days old can feed at least five of these nestlings enough to ensure their survival . The standardized body mass of parents (SBM), which was defined as the body mass divided by the length of the tarsus, did not differ among brood sizes, or throughout the season. It is possible that the relationship between the constancy of the SBM and the seasonal decline in the body mass of nestlings indicates that bull‐headed shrikes have a limit to their parental efforts.

EGG HATCHABILITY INCREASES WITH COLONY SIZE IN CLIFF SWALLOWS

Abstract The percentage of otherwise successful nests containing ≥ 1 unhatched egg in Cliff Swallows (Petrochelidon pyrrhonota) varied inversely with colony size in southwestern Nebraska. Colony-site characteristics other than colony size had no significant effect on egg hatchability. The incidence of unhatched eggs at a colony site did not vary significantly with year, mean date of first egg laying, mean incubation period, extent of ectoparasitism, or mean body mass of nestlings or adults. This suggests that increased hatching failure in smaller colonies was unrelated to ectoparasitism by fleas and cimicid bugs, foraging success, or egg inattendance. Furthermore, because reproductive interference and incidence of brood parasitism do not increase in smaller colonies, these variables seem unlikely to account for the relationship between egg hatchability and colony size. More frequent matings between genetically similar individuals and reduced opportunities for females to seek extrapair fertilizations with ...

The individual optimization of fitness: variation in reproductive output, including clutch size, mean nestling mass and offspring recruitment, in manipulated broods of great tits Parus major

The individual optimization of fitness: variation in reproductive output, including clutch size, mean nestling mass and offspring recruitment, in manipulated broods of great tits Parus major

The individual optimization of fitness: variation in reproductive output, including clutch size, mean nestling mass and offspring recruitment, in manipulated broods of great tits Parus major

Abstract The functional prediction of the Individual Optimization Hypothesis (Pettifor et al. 1988) is explicitly tested, namely that ‘the optimal clutch size is n for birds that choose to lay n eggs, regardless of the actual value of n’ (Högstedt 1980). Over a 10‐year period, we examine the recruitment from 1392 nests of great tits, 575 of which had their brood size experimentally manipulated. We defined final manipulation as the difference between the number of young ringed and the original clutch size. Mean nestling mass declined with final manipulation: those broods from which young were removed had a significantly higher mean fledging mass than control broods, which in turn fledged at a higher mass than those from nests to which young had been added. There was a significant difference in the strength of this effect between years. Addition nests (final manipulation ≥ 2 young) fledged significantly more offspring (x̄ = 10·96, SE = ± 0·16, n = 167) than control nests (final manipulation =−1, 0 or +1 young; x̄ = 8·68, SE = ± 0·07, n = 646), which fledged significantly more young than removal nests (final manipulation ≤ 2 young; x̄ = 5·68, SE = ± 0·09, n = 579). Recruitment per nest (the key measure upon which selection would act since parental survival was independent of manipulation in this study) was greatest for parents rearing a brood size equal to their own clutch size. Averaged over the 10 years, a Poisson model of the number of young recruited per nest showed maximal recruitment to occur at a final manipulation of 0·42 extra young added to the original clutch size. This final manipulation value was not significantly different from zero manipulation (i.e. when parents rear the same size of brood as their original clutch size). Using a restricted data set, where there was no loss of young through egg‐hatch failure and/or loss of very small young, and examining recruitment per nest with respect to experimental manipulation, indicated maximal recruitment to occur at a manipulation of an additional 0·44 young. The recruitment from this experimental manipulation was not significantly different from zero manipulation (i.e. control broods). The original size of clutch laid by a female was indicative of the ‘condition’ of the parents. Manipulation of brood size showed that birds naturally laying larger clutches were ‘fitter’ than birds laying smaller clutches in that, when comparing birds that were all made to rear the same brood size, those with young removed recruited more young than control parents, which in turn recruited more young than those parents to which young had been added to the nests. There were significant differences between years in the shape of recruitment per nest relative to the extent of both final and, separately, experimental manipulation, but in no year did addition broods recruit significantly more offspring than control broods. All these results are consistent with the Individual Optimization Hypothesis – individual optimization via phenotypic plasticity is the most parsimonious functional explanation for the observed variation in the range in size of clutch laid by individuals.