THE INFLUENCE OF BROOD SIZE ON THE ENERGY METABOLISM AND WATER LOSS OF NESTLING GREAT TITS PARUS MAJOR MAJOR

At normal outdoor temperatures there is a distinct influence of brood size on the heat production of ten-day-old Great Tits. One ten-day-old nestling proved unable to maintain its body temperature at 12^°C. Two ten-day-old tits together in one nestbox at 12^Á°C were able to elevate the air temperature sufficiently to maintain homoiothermia. The same of course holds for tits in larger broods.
At an air temperature of 18^°C, six or seven ten-day-old tits placed in a nestbox elevated the air temperature to a level at which they almost reached a state of hyperthermia: their metabolism was at the basal level. The basal metabolism of a ten-day-old tit was found to be slightly more than 0–1800 kcal/h. The metabolism intensity of 12 tits in a nestbox at 12^°C was of the same order of magnitude.
Tits in broods comprising more than 12 or 13 nestlings at normal outdoor temperatures probably develop hyperthermia, which is unfavourable both for their energy and for their water balance.     

FOOD, FEEDING RATES AND BODY TEMPERATURE IN THE NESTLING HOUSE SPARROW PASSER DOMESTICUS AT OXFORD

Diet, feeding frequency and body temperatures were studied in nestling House Sparrows at Oxford. In the diet, studied principally from crop contents, dipterous flies, caterpillars and aphids were most prominent in early May, early June and July respectively, while bread and dry grain, apparently less suitable foods, were more evenly distributed throughout the breeding season but apparently acquired an importance when insect foods were scarce.
Adult House Sparrows increased the frequency of their feeding visits to the nestlings proportionately with brood-size for broods of 1–3, but for larger broods the feeding frequency did not increase. This abruptly achieved upper limit presumably gave rise to inadequate feeding of the larger broods (including the principal brood-size). The male's share of the visits decreased markedly in the later stages of the nestling period, corresponding to his initiation of a display directed at the female. His displaying at this stage probably allows the female to begin a further clutch soon after the previous nesting has finished.
Nestlings were unable to maintain a steady body temperature above the ambient air temperature outside the nest before nestling day 10½. Maintenance of a steady body temperature depends on the nestling's feather covering, which is effectively complete at 9½ days. Before this, temperature control is possible within a limited range of ambient temperatures.     

Blood sampling does not affect fledging success and fledgling local recruitment in coal tits ( Parus ater)

In order to assess the potentially harmful consequences of blood sampling in nestling coal tits (Parus ater), we analysed fledging success, fledgling local recruitment and recruit natal dispersal for nestlings originating from 27 blood-sampled broods and nestlings from 39 control broods. No adverse effects of blood sampling were detectable.     

Effects of temperature and nest heat exposure on nestling growth,dehydration and survival in a Mediterranean hole‐nesting passerine

Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double‐brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra‐seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest‐site choice. Ambient temperature changed greatly during the chick‐rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus‐length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing‐length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun‐exposed to sun‐protected nest‐sites as the season progresses. However, nest‐site availability and competition for sites are likely to impose constraints on this choice.     

Immune function and survival of great tit nestlings in relation to growth conditions

Life history theory predicts a trade-off between number and quality of offspring. Reduced quality with increasing brood size may arise from a decrease in body condition or in immunocompetence that would be important in fighting off virulent parasites by immunologically naive offspring. We tested the effect of rearing conditions on immune function of nestling great tits (Parus major) by reducing or increasing broods by two hatchlings. In the middle of the nestling period (on day 8), nestlings from enlarged broods developed lower T cell responses [as measured from the cutaneous swelling reaction to injection with phytohaemagglutinin (PHA)] and tended to have lower total leukocyte and lymphocyte concentrations in their peripheral blood than nestlings from reduced broods. Brood size manipulation affected the PHA response of nestlings most strongly in small clutches, suggesting that nestling immune function was dependent on their parents’ condition, as estimated by original clutch size. Intra-brood differences in nestling mortality were unrelated to immune parameters, but nestlings in broods without mortality had a stronger PHA response, higher concentration of lymphocytes and higher body mass on day 15 than nestlings in broods with mortality. These results support the prediction that the immune function of altricial birds is affected by rearing conditions, and that growth and immune parameters are related to inter-brood differences in nestling survival. Received: 1 February 1999 / Accepted: 19. July 1999     

Habitat and diet variability of two coexisting tit species in central European forests

Capsule: Blue Tits and Great Tits occupied different habitats within forests in Central Europe but their nestlings shared a similar diet.

Aims: To quantify the differences in offspring diet and territory habitat between Great Tits Parus major and Eurasian Blue Tits Cyanistes caeruleus in two European forests, and to test whether the ecological niches of the two species overlap.

Methods: Research was conducted on Great Tits and Eurasian Blue Tits, breeding in nest boxes in two forests near Kraków, Poland, during years: 2009, 2011 and 2012. Nine days after hatching, food items were collected from offspring using neck-collars. Habitat parameters surrounding each nest box were quantified.

Results: Great Tit territories were in old Oak-Hornbeam forest, whereas Blue Tits often nested in mixed forest. There were no significant differences between the two bird species in the variation in their caterpillar diets for which both species were highly variable. Great Tits collected more caterpillars of Noctuidae per nest than did Blue Tits in 2009 and 2011 in Niepo?omice Forest; Blue Tits collected more Tortricidae in 2011 and more spiders every year. In Krzyszkowice Forest in 2012, tits fed their nestlings in different periods and did not differ in the proportion of caterpillars. Habitat affected diet differently in each species.

Conclusion: Although Great Tits and Blue Tits occupied different territories in each forest and year of research, the diets of both species’ nestlings contained similar species of invertebrates. The overlaps of the birds’ environmental needs are specific at a local scale.     

Experimental study of alarm calls of the oriental tit (Parus minor) toward different predators and reactions they induce in nestlings

Anti-predatory strategies of birds are diverse and may include predator-specific alarm calls. For example, oriental tit (Parus minor) parents can distinguish snakes from other predators and produce snake-specific referential vocalizations ("jar" call) when a snake poses a threat to their nest. The “jar” call has a very specific function to induce fledging of nestlings close to fledging age. This reaction ensures nestlings' survival in natural encounters with snakes that are capable of entering nest cavities and kill entire broods. Sciurid rodents, like chipmunks, may pose a similar threat to cavity-nesting birds. We explored the hypothesis that parents use the fledging-inducing alarm vocalizations in this situation, because chipmunks, like snakes, can kill the brood upon entering the nest cavity. We compared alarm calls of parents toward two predators (chipmunk and snake) who pose a similar threat to the nestlings in a nest cavity, and toward an avian predator (Eurasian jay) who cannot enter nest cavities and poses no threat to the nestlings in a nest. Our results show that the vocal responses of oriental tits were different among the three predators. This suggests that the acoustic properties of vocal responses to predators are different between predators of a similar hunting strategy (nest-cavity entering). The playback of recorded vocal responses of parents to chipmunks did not trigger the fledging of old nestlings, whereas the vocalizations toward a snake did, as shown by earlier studies. Our study suggests that the vocal response of parents does not carry information about the ability of predators to enter the nest cavity and confirms the special status of alarm calls triggered by snakes.     

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.     

Removal of a nest-mate elicits an age-dependent increase in plasma corticosterone of nestling Black-legged Kittiwakes

ABSTRACT.   Plasma corticosterone concentrations in birds often increase about 3 min after exposure to a stressor such as capture and handling. When measuring adrenal responsiveness of nestlings in broods with more than one nestling, standardizing capture protocols to equalize the stressor among nestlings if they simultaneously perceive the presence and activity of a researcher as a stressor is logistically difficult. The objective of our study was to determine if nestling Black-legged Kittiwakes ( Rissa tridactyla ) in broods of two mount a corticosterone response when the first nestling is removed from the nest or, alternatively, if each initiates a corticosterone response only at the time it is handled. We obtained blood samples from one nestling within 3 min of initial disturbance of the nest, and then removed and sampled its sibling 10 min later. For younger nestlings, we found no difference in corticosterone levels between those sampled at 3 min and their sibling sampled at 10 min. In contrast, older nestlings sampled at 10 min after initial nest disturbance had elevated corticosterone levels compared to those sampled within 3 min. In addition, nestlings sampled within 3 min of capture had elevated corticosterone when exposed to protracted periods of investigator disturbance at nearby nests. Our results suggest that it is necessary to treat initial disturbance of the nest as the onset of the stress response for all nestlings in multi-nestling broods when handling older nestlings or nestlings of unknown age. In addition, for species that nest in dense colonies, the presence of an investigator at one nest may be a stressor for nestlings in adjacent nests.     

Do great tits (Parus major) starve to reproduce?

To test whether nest abandonment is associated with parental health state, reproductive parameters and parental condition indices were examined in relation to brood desertion in great tits. Before desertion, pairs that abandoned their broods in the second half of the nestling period had significantly higher nestling mortality as well as lower average weight of nestlings and entire broods. Independently of brood size, female great tits that deserted their broods on average weighed 1 g (>5%) more than non-deserters. Comparison of metabolic profiles revealed that deserting females were in better nutritional condition (inclined to fat deposition) than non-deserters, which showed symptoms of postresorptive catabolic state, as indicated by a lower level of plasma triglycerides, very low density lipoproteins, and a higher level of free fatty acids and β-hydroxy-butyrate. These results suggest that desertion can be regarded as a reproductive restraint and that non-deserting females invested at least some of their maintenance resources on brood rearing. We found no evidence that desertion or non-desertion was associated with age- or disease-related differences in residual reproductive values. Male condition was not related to brood abandonment, suggesting that desertions were primarily initiated by females. Received: 16 November 1998 / Accepted: 1 February 1999     

Intraseasonal effects of clutch manipulation on parental provisioning and residual reproductive value of eastern phoebes (Sayornis phoebe)

Summary First clutches of double-brooded eastern phoebes Sayornis phoebe were manipulated (up two eggs, down 2 eggs or no change) to test for intraseasonal reproductive tradeoffs and to test whether size of first brood influenced food delivery rates to nestlings and nestling quality in second broods.Considering all nests from both broods, rate of feeding nestlings increased linearly with brood size but nestling mass per nest decreased with increasing brood size. High nestling weights in small broods may have resulted from parents delivering better quality food, but we did not test this.Among treatment groups in first broods, nestlings from decreased broods weighed more than those in control or increased broods. Treatment did not influence the likelihood that second nests would be attempted after successful first nests nor did it alter the interval between nests. Nestlings of parents that renested weighed more than those of parents that did not, regardless of treatment, suggesting that post-fledging care may preclude renesting. Mass of individual females did not change between broods, regardless of brood size. Clutch sizes of second attempts were not affected by manipulations of first broods but increasing first broods reduced the number of nestlings parents were able to raise to day 11 in their second broods. However, manipulation of first broods did not affect mean nestling mass per nest of nestlings that survived to day 11.In phoebes, parents of small first broods are able to raise nestlings in better condition. We predict that in harsh years, parents of small first broods would be more likely to renest. Parents of enlarged first broods sacrificed quality of offspring in second broods, which seems a reasonable strategy if nestlings from second broods have lower reproductive value.     

Variation in plumage colour of the Great tit Parus major in relation to habitat, season and food

The plumage colour of nestling and adult Great tits Parus major major L. was studied at Trondheim (63 °N, 10 °E), Norway. Nestlings reared in deciduous woodland were yellower than those reared in coniferous woodland, those reared in 1983 were yellower than those in 1982, and the later in the breeding season they were reared the more yellow they were. Furthermore, adults were yellower than nestlings, and for both groups the males were yellower than the females. Experimental interchange of eggs between nests showed that the variation in plumage colour observed between broods was related primarily to the food and not to genetic differences. Sampling, by the neck-collar method, of the food brought by the parent birds showed that the yellower nestlings received a greater proportion of lepidopteran larvae, in particular greenish-coloured ones, than did the nestlings with a paler plumage. A speculation is whether or not the variation in plumage colour has some adaptive value (viz. background matching).
In avian systematics, plumage coloration has been used to distinguish and describe subspecies. The present study shows that such a classification should only be made with certain reservations, until possible variation in the food quality of the subspecies is known to have no influence on plumage coloration.     

Predator-Specific Effects on Incubation Behaviour and Offspring Growth in Great Tits

In birds, different types of predators may target adults or offspring differentially and at different times of the reproductive cycle. Hence they may also differentially influence incubation behaviour and thus embryonic development and offspring phenotype. This is poorly understood, and we therefore performed a study to assess the effects of the presence of either a nest predator or a predator targeting adults and offspring after fledging on female incubation behaviour in great tits (Parus major), and the subsequent effects on offspring morphological traits. We manipulated perceived predation risk during incubation using taxidermic models of two predators: the short-tailed weasel posing a risk to incubating females and nestlings, and the sparrowhawk posing a risk to adults and offspring after fledging. To disentangle treatment effects induced during incubation from potential carry-over effects of parental behaviour after hatching, we cross-fostered whole broods from manipulated nests with broods from unmanipulated nests. Both predator treatments lead to a reduced on- and off-bout frequency, to a slower decline in on-bout temperature as incubation advanced and showed a negative effect on nestling body mass gain. At the current state of knowledge on predator-induced variation in incubation patterns alternative hypotheses are feasible, and the findings of this study will be useful for guiding future research.     

杂色山雀亲代喂食与子代乞食间的行为

在育雏期,晚成鸟的子代一般都是由双亲共同来抚育,子代为了更好地存活,会用自己的方式竞争获得更多的食物和更好的生存空间,同时亲代也会根据子代的乞食信号来分配食物。2011年3～7月采用针孔摄像技术录制了杂色山雀(Parus varius)育雏期巢内亲代与子代间的行为,统计了亲鸟站位、雏鸟站位、雏鸟乞食强度及亲鸟的喂食情况等数据。分析结果表明:(1)雌雄亲鸟在巢中的站位各有特点,雄鸟在整个育雏期都喜欢站在距离巢口较近的位置;雌鸟站位不太固定,前期离巢口相对较远,中期和后期离巢口相对较近;(2)雏鸟离亲鸟越近,乞食强度越大,获得食物的机会就越多;离亲鸟越远的雏鸟越不爱乞食,所以站位对雏鸟的食物获得影响最大;(3)雌鸟承担主要的育雏任务,喂食频率远大于雄鸟;(4)育雏期的不同阶段雏鸟乞食强度、亲鸟喂食频率变化很大:中期雏鸟乞食强度最大,亲鸟喂食频率最高,后期雏鸟乞食强度最弱;(5)整个育雏期雌性亲本没有表现出明显的偏爱行为,但雄性亲本在中、后期更偏爱体型大的雏鸟。可见杂色山雀子代的行为和体型大小影响着亲代的食物分配,亲代也会根据雏鸟日龄调整站位和喂食行为。     

Low frequency of extra-pair fertilisations in House Sparrows breeding at high density

The importance that the density of breeders has on the opportunity for extra-pair fertilisations (EPFs) is controversial. Some evidence supports the idea that population density and frequency of extra-pair paternity are positively associated, whereas other work does not. In the present paper we estimate EPF frequency in a dense House Sparrow Passer domesticus colony. We detected extra-pair nestlings in 9.3% of 54 broods studied, and 7% of 171 nestlings were sired by extra-pair fathers. The number of clutches laid per female, the change of male or female between two consecutive breeding attempts and the age of the partners showed no association with the presence or absence of extra-pair fertilisations. Morphometric variables of paired males and females did not discriminate broods with EPFs from those without. We detected a single case of a female laying a "parasitic" egg in the nest of a male that in a previous breeding attempt was the extra-pair genetic father of her entire brood. The frequency of extra-pair fertilisation recorded in this study was low compared with that in other House Sparrow populations breeding at lower densities, or other species that breed in colonies. This result does not support the claim that EPF frequency is associated with population density. We propose, as an explanation for this result, that under high intra-sexual competition for nest sites (1) males may have limited opportunities to search for females for extra-pair copulations and (2) the high quality of male nest-owners may reduce female propensity to search for additional sexual partners.     

The pattern of Dunlin Calidris alpina distribution and abundance in relation to habitat variation in the Flow Country of northern Scotland

Capsule Folivorous caterpillars constituted the majority of nestlings’ food in a primeval forest. Blue Tit broods only partially matched the caterpillar peak, and the mismatch did not affect food composition or nesting success.

Aims To describe factors influencing the timing of reproduction in Blue Tits under primeval conditions (Bia?owie?a National Park, Poland) and to check whether they schedule breeding so as to synchronize broods with a seasonal caterpillar peak.

Methods We gathered information on phenology of leaf development, seasonal availability of folivorous caterpillars (frass collection), timing of Blue Tit breeding, composition of its nestling food, and nest fate over a three-year period.

Results Caterpillars constituted c. 74% of nestling diet, but only 17–65% of broods matched the caterpillar peak in any season. Neither total nest loss, nor frequency of brood reduction depended on the level of mismatch. Caterpillar availability was probably adequate every year, regardless of the amount of mismatch, and no selective advantage of precise matching was detectable. Phenological events at all trophic levels occurred earlier in warmer springs. Egg-laying coincided with tree bud burst and appearance of caterpillars, but was not critically dependent on their timing.

Conclusion The observations are consistent with the view that Blue Tits under primeval conditions in Bia?owie?a National Park, Poland, breed as early as possible, rather than synchronizing their breeding with the caterpillar peak later in the season.     

Brood size and begging intensity in nestling birds

Theoretical models suggest that sibling competition should selectfor conspicuous begging signals. If so, begging intensity mightbe expected to increase with the number of competitiors. Thepurpose of our study was to examine the relationship betweenbegging intensity and brood size using nestling tree swallows(Tachycineta bicolor) as our model. Over 2 years, we videotapedbegging behavior in unmanipulated broods of different sizes.We found that begging intensity increased with brood size. Theaverage weight of nestlings in each brood did not vary withbrood size, but feeding rate per nestling decreased with broodsize, suggesting that nestlings in larger broods begged moreintensively, possibly because they were hungrier. We also conductedan experiment to examine the effect of nest mates on beggingin different-sized broods. We found that nestlings with similarweights, previous competitive environments, and food deprivationbegged more intensively in large broods than in small broods.Overall, our study indicates that begging intensity increaseswith brood size in tree swallows. This relationship may resultfrom interactions among brood mates rather than from lower feeding rates to individual nestlings in larger broods.     

Adaptive host-abandonment of ectoparasites before fledging? Within-brood distribution of nest mites in house sparrow broods

We studied the within-brood distribution of a haematophagous mite Pellonyssus reedi living on nestling house sparrows (Passer domesticus) near the time of fledging. We measured the natural level of infestation of individual nestlings, and determined the feeding efficiency of mites, by scoring their feeding status. Within-brood distribution of mite loads was unrelated to nestling body mass, tarsus length, or immunocompetence. These results did not support parasite preference for large or susceptible hosts. Mite feeding-efficiency was also unrelated to these nestling characteristics, confirming that large nestlings or nestlings with less-developed immunocompetence did not provide superior feeding conditions for mites. Therefore, our results do not support the hypothesis that within-brood distribution of avian ectoparasites is explained by the parasites' preferences for characteristics, such as large body size or low immunocompetence, that make nestlings suitable hosts. On the other hand, we found that mite loads were negatively correlated with nestling age and feather length, suggesting that nestlings closer to fledging harbored fewer mites then their less-developed nestmates. Furthermore, feather length had a stronger relationship with parasite distribution than did nestling age. We presume, therefore, that feather characteristics, i.e., length, may serve as a signal for mites to perceive the ready-to-fledge state of nestlings, inducing abandonment behavior. These results support another, largely neglected hypothesis, i.e., that the avoidance or abandonment of those nestlings that are close to fledging may also explain the parasites' distribution in a brood. This hypothesis is based on the argument that many nest-dwelling ectoparasites breed in the nest material and emerge only periodically to feed on nestlings. In such parasites, the ability to recognize and avoid mature fledglings can be adaptive because this may help the parasites to avoid their removal from the nest so they can continue to reproduce by feeding on unfledged chicks of the current or later broods. Our results suggest that adaptive host-abandonment by nest-dwelling ectoparasites can influence within-brood parasite distributions around the time of fledging.     

Chick loss from mixed broods reflects severe nestmate competition between an evictor brood parasite and its hosts

Hatchlings of the obligate brood parasite common cuckoo Cuculus canorus typically evict eggs and nestmates but, rarely, host and parasite nestlings may grow up together. As part of previous experiments, we manipulated host clutches by inducing two great reed warbler Acrocephalus arundinaceus and one parasite young to share a nest from 4 days posthatch, when the cuckoo's eviction behaviour is thought to cease. We documented that in mixed broods typically at least one nestling eventually fell out of nest during the period of 5-10 days posthatch. In 83% of nests one or two host chicks disappeared, and in 17% of nests parasite chicks were lost. All nestlings remained in control broods of three hosts or one parasite. These results imply strong physical competition for space in mixed broods. We suggest that continued foster care for parasitized broods may occasionally be beneficial because host nestlings have some chance to escape the costs of parasitism, even when their parents fail to reject the parasite's egg and the parasite hatchling fails to evict nestmates. Conversely, evictor parasite chicks benefit not only through improved growth, as reported before, but also through the elimination of nestmate competition for space and the risk of displacement from mixed broods.     

Production and costs of nesting attempts in Snow Buntings Plectrophenax nivalis: why do they attempt second broods?

During 1988–1993, pairs of Snow Buntings Plectrophenax nivalis on our study sites in northeast Scotland reared an average of 1.2 broods. Clutch sizes of first and second broods were similar, but partial losses were greater in second broods, leading to a difference of at least 40% in overall nest productivity between successful first and second broods. Over and above this, total nest failure was four times higher in the second broods, and autumn sightings of ringed nestlings from second broods were only a third of those of first-brood nestlings. As a result, second broods produced a mere 10% of future recruits to the breeding population. However, there was also little evidence of costs associated with producing, or attempting to produce, second broods. Young from first broods were not less likely to reach independence if a second brood was attempted, between-year return rates of double-brooded adults were similar to those of single-brooded birds and double-brooded adults did not appear to be less fecund in the following summer. Therefore low costs to the adults of attempting second broods may allow the continuation of a strategy which appears to have only a marginal influence on overall reproductive success in the area studied.