Traffic noise exposure affects telomere length in nestling house sparrows

In a consistently urbanizing world, anthropogenic noise has become almost omnipresent, and there are increasing evidence that high noise levels can have major impacts on wildlife. While the effects of anthropogenic noise exposure on adult animals have been widely studied, surprisingly, there has been little consideration of the effects of noise pollution on developing organisms. Yet, environmental conditions experienced in early life can have dramatic lifelong consequences for fitness. Here, we experimentally manipulated the acoustic environment of free-living house sparrows (Passer domesticus) breeding in nest boxes. We focused on the impact of such disturbance on nestlings’ telomere length and fledging success, as telomeres (the protective ends of chromosomes) appear to be a promising predictor of longevity. We showed that despite the absence of any obvious immediate consequences (growth and fledging success), nestlings reared under traffic noise exposure exhibited reduced telomere lengths compared with their unexposed neighbours. Although the mechanisms responsible for this effect remain to be determined, our results provide the first experimental evidence that noise alone can affect a wild vertebrate''s early-life telomere length. This suggests that noise exposure may entail important costs for developing organisms.     

Fitness-related consequences of egg mass in nestling house wrens

The fitness-related consequences of egg mass, independent of confounding influences associated with parental quality, remain poorly understood for wild birds in general and for passerines in particular. We performed cross-fostering experiments to test the hypothesis that egg mass, independent of parental quality, is the primary determinant of fitness-related traits in nestling house wrens (Troglodytes aedon), an insectivorous passerine. Nestling mass was significantly correlated with the mass of the eggs from which nestlings hatched early but not late in the nestling period in early-season broods. In contrast, in late-season broods, nestling mass was correlated with egg mass until nestlings achieved asymptotic mass. Neither nestling growth nor survival to nest leaving was related to egg mass in either early- or late-season broods; however, nestlings in late-season broods grew more slowly than did nestlings in early-season broods. We propose that nestling mass and egg mass remained correlated throughout the nestling period in late-season broods because decreased arthropod food resources late in the breeding season constrain parents'' ability to provision nestlings. We conclude that female house wrens in this population trade-off clutch size for greater egg mass to maximise reproductive success in late-season broods.     

Behavioural responses to ectoparasites in pied flycatchers Ficedula hypoleuca: an experimental study

Nests of cavity‐nesting birds usually harbor some species of haematophagous ectoparasites that feed on the incubating adults and nestlings. Given the negative impact of ectoparasites on nestlings there will be selection on hosts to reduce parasite infestations through behavioural means. We have experimentally reduced the abundance of all ectoparasites in nests of pied flycatchers Ficedula hypoleuca to explore both whether there are changes in the frequency and duration of putative anti‐parasite behaviours by tending adults, as well as whether such anti‐parasite behaviours are able to compensate for the deleterious effects that parasites may have on nestlings. Heat treatment of nests substantially decreased the density of ectoparasites, and thereby positively affected nestling growth. The frequency and intensity of female grooming and nest sanitation behaviours during the incubation and nestling periods decreased as a consequence of the experimental reduction of ectoparasite infestation. Although nestlings begged more intensely in infested nests, the experiment had no significant effect on parental provisioning effort. Reduction of parasites resulted in larger nestlings shortly before fledging and increased fledging success. This study shows a clear effect of a complete natural nest ectoparasite fauna on parental behaviour at the nest and nestling growth in a cavity‐nesting bird. Although ectoparasites induce anti‐parasite behaviours in females, these behaviours are not able to fully remove parasite's deleterious effects on nestling growth and survival.     

Plastic and the Nest Entanglement of Urban and Agricultural Crows

Much attention has been paid to the impacts of plastics and other debris on marine organisms, but the effects of plastic on terrestrial organisms have been largely ignored. Detrimental effects of terrestrial plastic could be most pronounced in intensively human-modified landscapes (e.g., urban and agricultural areas), which are a source of much anthropogenic debris. Here, we examine the occurrence, types, landscape associations, and consequences of anthropogenic nest material in the American crow (Corvus brachyrhynchos), a North American species that breeds in both urban and agricultural landscapes. We monitored 195 nestlings in 106 nests across an urban and agricultural gradient in the Sacramento Valley, California, USA. We found that 85.2% of crow nests contained anthropogenic material, and 11 of 195 nestlings (5.6%) were entangled in their nests. The length of the material was greater in nests in agricultural territories than in urban territories, and the odds of entanglement increased 7.55 times for each meter of anthropogenic material in the nest. Fledging success was significantly lower for entangled than for unentangled nestlings. In all environments, particularly urban, agricultural, and marine, careful disposal of potential hazards (string, packing and hay bale twine, balloon ribbon, wire, fishing line) could reduce the occurrence of entanglement of nestling birds.     

Begging in Common Redstart Nestlings: Scramble Competition or Signalling of Need?

Begging behaviour by the young affects parental food distribution among nestlings of altricial birds. We present an analysis of two types of begging behaviour (assuming the front nest positions and gaping) based on videotaped natural nestling feeding in European common redstart (Phoenicurus phoenicurus). We test whether these types of begging support the predictions of two mathematical models: scramble competition with competitive asymmetries between nestlings [Anim. Behav. 27 (1979) 1210] or honest signalling model [Nature 352 (1991) 328]. None of the measured variables of nestling or parental behaviour were affected by body weight differences between siblings. In contrast, both gaping and nest positioning were affected by individual differences in nestling hunger. In agreement with the honest signalling model, hungrier nestlings gaped with higher probability and started to gape sooner after the arrival of the parent than did their less hungry nestmates. Those nestlings with the shortest latency to gape also received food more often. Nest positioning was related to nestling hunger in a way unforeseen by the existing models. The intervals between nestling position changes were several times longer than the intervals between parental feeding visits, and parents preferred to feed nestlings in front positions, so nestlings in front positions were always less hungry than nestlings in back. Hence the pattern of movements influenced the feeding decision in favour of the more satiated nestlings and acted against the effect of gaping. Nestling movement seemed to be caused by the less hungry nestlings moving actively from front to rear positions. Low mortality of individual nestlings within broods that survived to fledging and small within‐brood variation in fledging weights indicated low competition among nestmates. We suggest that there are two behavioural mechanisms that contribute to the equalization of fledging weights in common redstart nestlings: the signalling of need through gaping and the regular turnover of nestlings at front positions.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows,Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows, Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.     

Experimental evidence for an impact of anthropogenic noise on dawn chorus timing in urban birds

Many animal species are living in urban areas, where they encounter human‐altered environmental conditions. Artificial light and traffic noise are two of the most prominent anthropogenic factors, both of which potentially affect animal life. Here we studied the changes in traffic noise conditions over the morning in the urban bird habitat of the city of Seville, Spain. We tested experimentally whether noise from human activities can cause a shift in the timing of birdsong activity. Our data revealed that noise conditions vary markedly among our replicate set of twelve streets. Relatively quiet streets show low base‐line amplitude levels early in the morning, with frequent events of brief noise bursts, followed by a strong rise in noise levels. Relatively noisy streets have high base‐line amplitude levels from a much earlier start in the morning. Experimental exposure data revealed a noise‐related earlier start of dawn singing for two out of six species: the spotless starling Sturnus unicolor and the house sparrow Passer domesticus. Our experiment did not cover earlier singing species and revealed no impact for species with more‐variable starting times of the dawn singing. Our study provides more insight into the intertwinings of bird and human behavior and confirms the potential for experimental approaches to successfully tackle questions related to the impact of anthropogenic factors on animal life in cities.     

Ectoparasites and host energetics: house martin bugs and house martin nestlings

We measured the energy cost of ectoparasitism in an experimental study of the house martin bug Oeciacus hirundinis and its main host, nestlings of the house martin Delichon urbica. Nests were randomly assigned to inoculation with 0 (control) 10, or 100 bugs during egg laying, and this resulted in statistically significant differences in parasite loads following fledging of nestlings. Parasite loads negatively affected house martin nestlings as estimated from their body mass at age 16 days and from mass loss estimated over 1 day late in the nestling period. Daily energy expenditure (KJ/d), average daily metabolic rate (ml CO₂/g h), and mass independent daily energy expenditure (kJ/mass^0.67d) did not differ significantly between experimental treatments. However, average daily metabolic rate increased with increasing intensities of ectoparasitism. Mass independent daily energy expenditure also increased with higher levels of parasite infestation. These results demonstrate that the bug imposes an energy cost on its host by elevating the level of metabolism.     

Developmental stress increases reproductive success in male zebra finches

There is increasing evidence that exposure to stress during development can have sustained effects on animal phenotype and performance across life-history stages. For example, developmental stress has been shown to decrease the quality of sexually selected traits (e.g. bird song), and therefore is thought to decrease reproductive success. However, animals exposed to developmental stress may compensate for poor quality sexually selected traits by pursuing alternative reproductive tactics. Here, we examine the effects of developmental stress on adult male reproductive investment and success in the zebra finch (Taeniopygia guttata). We tested the hypothesis that males exposed to developmental stress sire fewer offspring through extra-pair copulations (EPCs), but invest more in parental care. To test this hypothesis, we fed nestlings corticosterone (CORT; the dominant avian stress hormone) during the nestling period and measured their adult reproductive success using common garden breeding experiments. We found that nestlings reared by CORT-fed fathers received more parental care compared with nestlings reared by control fathers. Consequently, males fed CORT during development reared nestlings in better condition compared with control males. Contrary to the prediction that developmental stress decreases male reproductive success, we found that CORT-fed males also sired more offspring and were less likely to rear non-genetic offspring compared with control males, and thus had greater overall reproductive success. These data are the first to demonstrate that developmental stress can have a positive effect on fitness via changes in reproductive success and provide support for an adaptive role of developmental stress in shaping animal phenotype.     

Increasing the perceived predation risk changes parental care in female but not in male Great Tits Parus major

In birds, little is known about how the presence of predators alters parental food distribution decisions among nestlings. We found that experimentally increasing perceived predation risk changed parental care in female but not in male Great Tits Parus major. Females fed the lightest and average nestlings at similar rates under control conditions when predation risk was not manipulated but ignored the lightest nestling under increased perceived predation risk. Moreover, females reduced the duration of nest visits greatly after encountering a model predator, suggesting that the perception of predators may facilitate brood reduction mechanisms.     

Effect of altitude on male parental expenditure in Mountain Bluebirds ( Sialia currucoides ): are higher-altitude males more attentive fathers?

Male investment of time and energy in caring for offspring varies substantially both between and within bird species. Explaining this variation is of long-standing interest to ornithologists. One factor that may affect male care is breeding site altitude, through its effects on climate. The harsher, less predictable abiotic conditions at higher altitudes are hypothesized to favour increased male investment of time and energy in offspring care. We tested this hypothesis by comparing male parental behaviour in Mountain Bluebirds (Sialia currucoides) nesting at 1500 and 2500 m a.s.l. in the Bighorn Mountains of Wyoming, USA. We compared rates of prey delivery to nestlings at these two altitudes at two times: 1–2 days after hatching, when females spend much of their time brooding young, and 12–13 days later, when brooding has ended and nestling energy demands are peaking. High-altitude males fed nestlings 18 and 28% more often than low-altitude males early and later in the nestling stage, respectively, but only the difference in late-stage feeding rates were significant. Like males, females at the high site also fed nestlings significantly more often than females at the low site later in the nestling stage (45% difference in feeding rates). Consequently, the proportion of all feeding trips made by males at the high site (40%) did not differ significantly from that at the low site (44%). Parents at the high altitude may feed nestlings more often to compensate for their greater thermoregulatory costs. Parents may also be attempting to assist nestlings in storing fat and/or attaining a large size and effective homeothermy as quickly as possible to enhance nestling ability to survive bouts of severe weather which are common at high altitudes.     

Facultative adjustment of pre‐fledging mass recession by nestling chimney swifts Chaetura pelagica

In species susceptible to mass‐dependent flight costs, mass recession prior to fledging may ensure that fledglings have appropriate wing loading. Our objectives were to determine if mass recession by chimney swift Chaetura pelagica nestlings is intrinsically controlled or facultatively adjusted by nestlings, and if mass recession is driven by changes in parental (i.e. reduced provisioning rates) or nestling (i.e. reduced begging) behavior. Nestling swifts (n = 50 in 17 broods) were divided into three treatment groups: controls, half‐weighted, or weighted. Half‐weighted and weighted nestlings had 0.6–0.7 or 1.2–1.3‐g lead weights, respectively, glued to body feathers on their backs during the period from 16 to 26 d post‐hatching. Weighted nestlings lost more mass than control and half‐weighted nestlings. After accounting for the added weights, control nestlings also had a higher wing loading than weighted nestlings. Video recordings revealed that provisioning rates of adult swifts did not vary throughout the nestling period, but the percent time nestlings spent begging increased slightly with age. Differences in mass recession among nestlings in different treatment groups resulted in convergence toward similar wing loading values likely optimal for flight efficiency. Mechanism(s) involved in this process remain unclear because provisioning rates were similar (from day 12 to 26 post‐hatching) whereas percent begging time by nestlings tended to increase with nestling age. However, weighted nestlings may have lost more mass than control nestlings by soliciting less food from adults than siblings, being more active, losing more water due to tissue maturation, or through some combination of two or more of these factors.     

Philornis infection in blue‐black grassquits: impact on nestlings and risk factors involved

Parasitic botfly larvae (Philornis ssp., Diptera: Muscidae) are found in nests of several bird taxa, although prevalence and impact on nestling survival vary considerably among species. Here we describe patterns of botfly infestation in blue‐black grassquit Volatinia jacarina nestlings. We identified the most typically affected nestling body parts and assessed parasite prevalence, impact on nestling survival, and changes in nestling body shape. Additionally, we tested whether climatic conditions, nest morphology and habitat characteristics are associated with larvae abundance. Blue‐black grassquits had low breeding success (16% of eggs/nestlings survived to fledged; 19% of the nests fledged at least one), but most failures resulted from predation by vertebrate predators. We estimated that 1% of nestlings died due to botfly infestation, and the number of subcutaneous larvae (range 1–18) in a nestling's body did not predict fledging success. Infected chicks exhibited higher tarsus asymmetry. Thus, we argue that although botflies had a small impact on offspring survival, they may reduce fitness in adulthood. There was no evidence that environmental conditions and nest morphology are linked to the number of larvae on nestlings. Nesting areas with higher food supply had lower infestation rates. Possibly, food‐rich habitats allow parents to invest more time in offspring care (brooding nestlings), thus protecting them from fly attacks. Alternatively, vegetation composition could influence local invertebrate diversity, which could provide a natural trophic buffer against adult Philornis. The present study brings to light new perspectives concerning bird–botfly interaction.     

Activity patterns during food provisioning are affected by artificial light in free living great tits (Parus major)

Artificial light may have severe ecological consequences but there is limited experimental work to assess these consequences. We carried out an experimental study on a wild population of great tits (Parus major) to assess the impact of light pollution on daily activity patterns during the chick provisioning period. Pairs that were provided with a small light outside their nest box did not alter the onset, cessation or duration of their working day. There was however a clear effect of artificial light on the feeding rate in the second half of the nestling period: when provided with artificial light females increased their feeding rate when the nestlings were between 9 and 16 days old. Artificial light is hypothesised to have affected the perceived photoperiod of either the parents or the offspring which in turn led to increased parental care. This may have negative fitness consequences for the parents, and light pollution may thus create an ecological trap for breeding birds.     

The effect of direct supplementary feeding of nestlings on weight loss in female Great Tits Parus major

Experimentally hand-feeding nestlings of enlarged (+3 nestlings) broods reduced female weight loss during the nestling period in a single-brooded Great Tit Parus major population in Scotland but did not affect nestling size. The result is consistent with the existence of a trade-off in parental care between reproductive costs and benefits.     

IBERIAN AZURE-WINGED MAGPIE CYANOPICA (CYANA) COOKI NESTLINGS BEGGING CALLS: CALL CHARACTERIZATION AND HUNGER SIGNALLING

ABSTRACT

Nestling begging behaviour has long been seen as a signal by which nestlings solicit care from parents and most of the existing evidence provides some support for it being an honest signal. Begging is a multicomponent signal in which both sound and vision components are usually important. Although it is known that begging encodes information about nestling hunger the present knowledge about the specific behavioural features that convey the information is still scarce. The aim of this study was to describe begging calls of Iberian Azure-winged Magpie Cyanopica (cyana) cooki nestlings and examine how information on nestling hunger might be encoded in the begging calls. Nestlings were experimentally submitted to different periods of food deprivation and the call variation within individuals was studied. The young were individually tested and stimulated to beg by simulating parental visits. When subject to increasing food deprivation periods, nestlings increased the response level to simulated parental visits. The study also found that for the studied size differences, nestlings did not differ in their response level. Results confirmed that information on nestlings' hunger might be encoded in parameters of the calling behaviour. When the food deprivation periods increased, nestlings tended to start begging earlier, begged more often, extended their calling bout and increased the call duration, changing both at the level of the call and vocal begging bout. Overall the results support the view of begging as an honest signal, namely that begging should reflect nestling hunger and that only some call features might encode information about hunger.     

Are offspring begging levels exaggerated beyond the parental optimum? Evidence from a bidirectional selection experiment

Parental care involves elaborate behavioural interactions between parents and their offspring, with offspring stimulating their parents via begging to provision resources. Thus, begging has direct fitness benefits as it enhances offspring growth and survival. It is nevertheless subject to a complex evolutionary trajectory, because begging may serve as a means for the offspring to manipulate parents in the context of evolutionary conflicts of interest. Furthermore, it has been hypothesized that begging is coadapted and potentially genetically correlated with parental care traits as a result of social selection. Further experiments on the causal processes that shape the evolution of begging are therefore essential. We applied bidirectional artificial selection on begging behaviour, using canaries (Serinus canaria) as a model species. We measured the response to selection, the consequences for offspring development, changes in parental care traits, here the rate of parental provisioning, as well as the effects on reproductive success. After three generations of selection, offspring differed in begging behaviour according to our artificial selection regime: nestlings of the high begging line begged significantly more than nestlings of the low begging line. Intriguingly, begging less benefitted the nestlings, as reflected by on average significantly higher growth rates, and increased reproductive success in terms of a higher number of fledglings in the low selected line. Begging could thus represent an exaggerated trait, possibly because parent–offspring conflict enhanced the selection on begging. We did not find evidence that we co‐selected on parental provisioning, which may be due to the lack of power, but may also suggest that the evolution of begging is probably not constrained by a genetic correlation between parental provisioning and offspring begging.     

Individual Consistency in Parental Effort Across Multiple Stages of Care in the House Sparrow, Passer domesticus

In many avian species in which biparental care is provided to offspring, substantial variation exists within members of each sex in the level of effort contributed to various forms of parental care. Questions remain as to whether individuals that contribute more toward one parental activity also contribute more toward other activities in which they participate. We examined the contributions of male and female house sparrows (Passer domesticus) to three forms of parental care: incubation, nestling provisioning, and nest defense, and compared the investments made by individuals at each stage of care relative to other same‐sexed parents. In both males and females, nestling feeding rates were positively associated with time spent incubating, but no relationships were found between measures of nestling feeding and nest defense. The predictability of an individual's feeding behavior based on earlier incubation efforts may make incubation a good stage for individuals to evaluate the parental abilities of their partners.     

Parental provisioning, nestling departure decisions and prefledging mass recession in Cassin's auklets

We investigated how parental provisioning and nestling departure behaviour interact to produce prefledging mass recession in Cassin's auklets, Ptychoramphus aleuticus. Under our hypothesis, auklet parents are reluctant provisioners and should be increasingly likely to terminate or reduce provisioning of their single nestling as it matures. For the nestling, remaining in the nest presents a risk of losing mass (if the parent does not provision) but also a possibility of additional provisioning. As the nestling matures and becomes increasingly capable of independence, the benefits of remaining in the nest decrease and nestlings should be increasingly likely to fledge. Nestlings also should be more likely to fledge when the expectation of additional provisioning is low. Data on parental provisioning (based on growth increments) and nestling departure were consistent with our hypothesis. Older and heavier nestlings had smaller growth increments than younger and lighter nestlings, suggesting that parents were reluctant to provision old and heavy nestlings. Older and heavier nestlings also were increasingly likely to fledge. We hypothesized that nestlings might use the intensity of mass loss to gauge parental reluctance to provision, and accordingly, nestlings were increasingly likely to fledge after experiencing a greater amount of mass loss. Copyright 1999 The Association for the Study of Animal Behaviour.