Begging Signals Research Articles

Escalated begging does not compromise nestling health

Abstract A widely accepted explanation for the reliability of offspring begging signals assumes a differential benefits model balanced by direct viability costs independent of offspring nutritional condition. However, supporting evidence for this idea is inconclusive and often hampered by methodological limitations, including differential stimulation protocols and reliance on single, potentially biased markers of nestling health. This study tested the existence of direct, intrinsic, and condition-independent allocation trade-offs between begging and body mass, immunity and oxidative stress by manipulating the begging effort of spotless starling (Sturnus unicolor) nestlings while maintaining constant food intake. We addressed potential problems of previous experimental protocols, ensuring uniform stimulation levels and evaluating multiple immune and oxidative markers. We observed no significant effects of experimentally increased begging effort in any of the 14 physiological markers analysed, with 95% confidence intervals of effect sizes consistently including zero or one (for the lysis capacity of plasma), indicating no biologically relevant effects. Overall, our findings suggest no physiological trade-offs associated with intense begging.

Immune challenge reduces begging effort and modifies begging call structure in spotless starling nestlings

Symptoms of illness offer insights into an organism’s condition, altering social signals that affect others’ behavior. Nestling birds employ begging signals to solicit parental care, but the extent to which begging reflects nestling health beyond hunger remains controversial. We investigated how experimentally induced changes in health affect begging signals in spotless starling (Sturnus unicolor) nestlings. To alter health status, we challenged nestlings by injecting lipopolysaccharide (LPS) -an antigen that elicits an immune response- or a control substance (PBS) and observed begging behavior under controlled food deprivation conditions. LPS-treated nestlings exhibited delayed gaping, reduced stretching, and less begging time compared to control nestlings. Moreover, LPS-treated nestlings produced calls with higher spectral entropy, particularly when deprived of food for longer. Our findings indicate that begging signals are sensitive to induced sickness. However, addressing mechanistic issues is crucial for effectively testing whether begging reflects nestling condition as a signal of quality in future experimental setups.

Differential impact of anthropogenic noise during the acoustic development of begging calls in Blue Tits (Cyanistes caeruleus)

In many bird species, nestling begging signals play a key role in the interaction between parents and their offspring during development. The information conveyed by begging calls can be disrupted by anthropogenic noise, which is one of the major threats to biodiversity in increasingly urbanized landscapes. Here, we describe the developmental change in acoustic structure of begging calls in nestling Eurasian Blue Tits Cyanistes caeruleus; begging calls are pure‐tone, low‐frequency, soft calls during the first days of development and gradually turn into white‐noise, hiss‐like, powerful calls of broadband frequency. This strong developmental variation highlights the importance of an extended sampling scheme in developmental studies. Furthermore, we pinpoint two phases where begging calls could be most vulnerable to masking by anthropogenic noise. First, during early development, begging calls are very soft and low‐pitched, closer to high‐intensity noise bands of traffic noise. Secondly, around day 11, begging calls show reduced tonality, which implies higher degradation, and relatively low amplitude, which implies reduced signal range. We encourage future research to describe acoustic development of begging calls in other species, to provide a robust foundation that will make noise mitigation policies more effective.

Norway rats help social partners in need in response to ultrasonic begging signals

AbstractBegging signals are widespread in animals and have been extensively studied in the context of brood care. In contrast, the functionality of begging signals expressed among adults has not yet been scrutinised experimentally. Norway rats (Rattus norvegicus) have been shown to express 50‐kHz calls towards a social partner when in need of help to obtain food. Here, we tested with help of playbacks whether focal subjects exposed to a high rate of ultrasonic calls would increase their helping rate towards their social partner. The propensity to help a partner was significantly enhanced when the focal rats were exposed to playback with a doubled number of calls relative to baseline conditions. To the best of our knowledge, this provides the first evidence of increased help in response to an experimentally altered begging signal in adult animals.

Investigating how different classes of nest predators respond to the playback of the begging calls of nestling birds

Begging brings benefits and costs for nestling birds: it can indicate their needs to their parents, but it can also be a cue used by predators to find the nest. The costs, like many variables related to nest predation, can be specific to what kinds of predators are present and their auditory capabilities. These costs and benefits could also be affected by human noise, as noise could disrupt communication to parents and eavesdropping by predators, although human-produced noise might be easily ignored if predators can hear high-frequency components of the begging. We studied nest predation on a generalist bird, the Red-whiskered Bulbul (Pycnonotus jocosus), in a tropical forest in which there are many kinds of nest predators, including birds, mammals and reptiles. In 20 natural nests in which artificial eggs were placed, and subsequently in 140 artificial nests, we broadcast recordings of begging nestlings, with and without traffic noise, at two volume levels. We hypothesized that playback would increase predation relative to a silent control, and that mixing in traffic noise with the begging would decrease predation, as the begging signal was masked. However, we hypothesized that some predators, particularly small mammals with sensitive high-frequency hearing, might ignore the traffic noise. We found that predation was lowest for the control treatment, and lower for treatments mixed with traffic noise than for those without it. Small mammals, however, showed an unexpected pattern, displaying less nest predation in the treatments with traffic noise. Our results demonstrate the human-associated noise can disturb nest predators and influence which kinds of predators use begging to locate nests.

Effects of a novel ectoparasite on condition and mouth coloration of nestling barn swallows

Abstract Parasites have profound and widespread implications for the ecology and evolution of hosts, and human activity has increased the frequency of interactions between hosts and parasites that have not co-evolved. For example, by building habitat attractive for nesting, humans might have facilitated range expansion by cliff swallows (Petrochelidon pyrrhonata) and barn swallows (Hirundo rustica) in North America, concurrently allowing a haematophagous ectoparasite of cliff swallows, the swallow bug (Oeciacus vicarious), to infest the nests of barn swallows. We found that in barn swallow nests infested with swallow bugs, nestlings weighed less and had lower haematocrit, and the within-brood variation in body mass and tarsus length was higher. Information about these negative effects might be available to parents via mouth coloration, a condition-dependent component of the begging signal. We found that nestlings from infested broods had lower-intensity carotenoid-based and ultraviolet mouth colours, although most elements of colour were unrelated to parasites. Host switching by the swallow bug offers excellent opportunities to understand the direct and indirect effects of a novel parasite and might also afford insights into how parasites cope with selective pressures exerted by closely related hosts with key ecological differences.

Size matters: shiny cowbirds secure more food than host nestmates thanks to their larger size, not signal exaggeration

Many hosts of obligate brood parasitic birds invest more in parasitic nestlings than they do in their own young. The shiny cowbird, Molothrus bonariensis, a generalist parasite, is fed at a higher proportion than its host nestmates when it is reared in nests of a smaller-bodied host, the house wren, Troglodytes aedon. We test two hypotheses that could account for this differential allocation of food by host parents. The signal exaggeration hypothesis states that cowbird chicks have visual and/or acoustic begging signals that elicit preferential feeding. The size-advantage hypothesis states that hosts preferentially feed large chicks and/or that larger chicks outcompete host chicks in a scramble competition for food. To gain insight into the relative importance of size versus species-specific signals on food allocation by house wrens, we performed audio and video recordings in nests with experimental broods of (1) a 2-day-old cowbird chick and a 2-day-old wren chick (different species, different size), (2) a 2-day-old cowbird chick and an 8-day-old wren chick (different species, same size) and (3) a 2-day-old house wren and an 8-day-old house wren (same species, different size). When cowbirds shared the nest with a same-size wren chick, both chicks received food in equal proportion. In contrast, larger chicks (both cowbirds and wrens) paired with small wren nestmates always received a higher food share. Cowbird begging behaviour and call traits differed from house wrens, but these differences did not always coincide with increased food. We conclude that, at least when cowbird nestlings are young (2 days old), their relatively large size accounts for the larger share of food they receive from house wren hosts, rather than some quality of their begging signal.

Size matters but hunger prevails-begging and provisioning rules in blue tit families.

It is commonly observed in many bird species that dependent offspring vigorously solicit for food transfers provided by their parents. However, the likelihood of receiving food does not only depend on the parental response, but also on the degree of sibling competition, at least in species where parents raise several offspring simultaneously. To date, little is known about whether and how individual offspring adjusts its begging strategy according to the entwined effects of need, state and competitive ability of itself and its siblings. We here manipulated the hunger levels of either the two heaviest or the two lightest blue tit (Cyanistes caeruleus) nestlings in a short-term food deprivation experiment. Our results showed that the lightest nestlings consistently begged more than the heaviest nestlings, an effect that was overruled by the tremendous increase in begging behaviour after food deprivation. Meanwhile, the amplified begging signals after food deprivation were the only cue for providing parents in their decision process. Furthermore, we observed flexible but state-independent begging behaviour in response to changes in sibling need. As opposed to our expectations, nestlings consistently increased their begging behaviour when confronted with food deprived siblings. Overall, our study highlights that individual begging primarily aims at increasing direct benefits, but nevertheless reflects the complexity of a young birds’ family life, in addition to aspects of intrinsic need and state.

Provisioning control during maternal care by the earwigAnisolabis maritima(Dermaptera: Anisolabididae): Do mothers adjust provisioning according to offspring need?

AbstractProvisioning offspring is an important form of parental care for the improvement of offspring survival and growth. Because provisioning can be costly for parents, parents may change their investment levels in response to offspring need and begging signals.Anisolabis maritimais a cosmopolitan species of earwig that shows subsocial behavior. Females progressively provision their young in soil burrows. The present study investigated whetherA. maritimamothers carry food to the nest for their offspring (nymphs) and whether the mothers adjust the amount of food carried to the burrow according to the degree of the nymphs’ hunger. Through laboratory experiments, I found that mothers carried food to sites where more nymphs were present, and more food to broods of more hungry nymphs. These results have revealed that mothers recognize the presence of offspring and the degree of their hunger. This study, therefore, indicates the presence of offspring begging signals inA. maritima.

Does host-absent vocalisation of common cuckoo chicks increase hosts’ food provisioning behaviour?

Parent-absent vocalisation is produced by nestlings of several bird families when the parents are away from the nest. An analogous behaviour, host-absent vocalisation, has been found in some species of avian brood parasites and there are several explanations why this behaviour could have evolved. Using playback experiments, we examined whether polygynous great reed warblers (Acrocephalus arundinaceus) adjust their food provisioning behaviour in response to host-absent begging vocalisation uttered by the common cuckoo (Cuculus canorus) chicks. We found that both on monogamous and polygynous nests, host pair members responded to the broadcasted parasite begging signals by increasing their feeding rates; yet, they did not deliver larger volumes of food as a consequence of somewhat smaller prey brought per visit. Nevertheless, we propose that host-absent vocalisation of the common cuckoo chick may still represent a signal of hunger that may compensate for other, deficient components of parasite begging display. However, the efficiency of this signal may be limited by the foster parents’ provisioning abilities and local prey availability. Bird chicks beg loudly for food when their parents are at the nest, as well as when the parents search for food elsewhere. The same applies to young parasites raised by their hosts. Experimental playback of host-absent begging calls of cuckoo chicks increased great reed warbler feeding frequency but had no effect on the volume of food delivered. Host-absent vocalisation may represent signal of hunger; however, its effectiveness may be limited by provisioning abilities of the hosts.

Complex feeding behaviour by magpies in nests with great spotted cuckoo nestlings

Parent decisions about food allocation are usually based on simple time‐saving rules that optimize their own fitness; however, they can sometimes vary depending on the prevailing ecological conditions both outside and inside the nest. Parent–offspring interactions also become more complex when parents suffer from brood parasitism, which implies that they care for the parasite's eggs and unrelated young. The great spotted cuckoo Clamator glandarius is a specialist brood parasite that uses the magpie Pica pica as its primary host. Here, by filming food allocation by magpie parents in natural non‐parasitized and experimentally parasitized and non‐parasitized magpie nests, we have found that magpie provisioning behaviour is highly complex including two types of feedings apart from normal ones. First, false feedings, when the parent touched the chick's beak but did not leave any food, occurred more frequently when feeding a cuckoo than when feeding magpie nestlings. Second, two types of what we have called coax feedings: 2a) when magpie parents induce a nestling to beg by waking it up by touching it softly with the beak, and 2b) when parents disregard begging signals (always from brood parasitic great spotted cuckoos) while coaxing one non‐begging nestling (always one of their own) to feed it. We suggest that brood parasitism, involving selfish excessively begging nestlings, could have acted as a selective pressure for both false and coax feedings to evolve, as both imply ignoring nestlings that beg too much. We also discuss that these parental responses could have evolved either by a discrimination without recognition mechanism, or, more probably, by a recognition‐based discrimination mechanism.

Nestlings reduce their predation risk by attending to predator-information encoded within conspecific alarm calls

Predation is one of the main threats to altricial nestlings, with predators often locating nests via eavesdropping on begging signals. Nestlings may be able to adjust their begging based on the current level of risk by monitoring both intra- and interspecific alarm calls near the nest. We show that noisy miner (Manorina melanocephala) nestlings can differentiate between terrestrial and aerial alarm calls of their own species, as they suppressed begging behaviour for longer in response to terrestrial rather than aerial alarm calls. This differential response is potentially due to greater danger that terrestrial calls encode. In contrast, nestlings ignored alarm calls of the sympatric grey butcherbird (Cracticus torquatus) and continued to beg but reduced begging intensity in response to the non-alarm calls of a sympatric eastern rosella (Platycercus eximius), suggesting nestlings were likely responding based upon similarity to a known signal as opposed to expressing a learnt behaviour. Results show that nestlings respond adaptively to two different intraspecific alarm signals but have not learnt to respond to the alarm calls of sympatric species. These suggest that nestlings are able to take advantage of the complex vocal repertoire that adults produce, although discernment is an issue when filtering out irrelevant stimuli.

No evidence that kin selection increases the honesty of begging signals in birds.

Providing plausible mechanisms to explain variation in the honesty of information communicated through offspring begging signals is fundamental to our understanding of parent–offspring conflict and the evolution of family life. A recently published research article used comparative analyses to investigate two long‐standing hypotheses that may explain the evolution of begging behavior. The results suggested that direct competition between offspring for parental resources decreases begging honesty, whereas indirect, kin‐selected benefits gained through saving parental resources for the production of future siblings increase begging honesty. However, we feel that evidence for a role of kin selection in this context is still missing. We present a combination of arguments and empirical tests to outline alternative sources of interspecific variation in offspring begging levels and discuss avenues for further research that can bring us closer to a complete understanding of the evolution of offspring signaling.

Begging and ectoparasite attraction

Honesty of offspring begging behaviours is the keystone to understanding the evolution of parent–offspring communication. Three main begging costs have been traditionally advocated that ensure the reliability of offspring signalling: energy expenditure, loss of inclusive fitness and attraction of predators. Here, we propose that ectoparasites may eavesdrop on begging signals, especially acoustic signals, for host detection, a never considered but potentially generalized cost of begging that will constrain the evolution of exaggerated begging displays. Ectoparasitic insects possess a diversity of auditory systems for intraspecific communication that may be used to detect begging calls of host offspring. The use of auditory cues for host detection offers some advantages to ectoparasites, particularly in environments in which long-distance detection of hosts is necessary. There are well-known examples of interspecific eavesdropping on host auditory signals by parasites that include parasitoid flies attracted to calling crickets and cicadas, and frog-biting midges and mosquitoes attracted to frog calls. Eavesdropping on begging signals may have evolved in those parasites searching for hosts that display begging behaviours, which include not only birds but also mammals and some reptiles and insects with parental care of juveniles. Considering begging costs due to detection by ectoparasites may help us understand the reliability, and therefore the evolution, of signals of need and parent–offspring communication.

Pied flycatcher nestlings incur immunological but not growth begging costs

Many theoretical models on the evolution of nestling begging assume this behavior is costly, so that only nestlings in real need of food would profit from giving intensive signals to parents. However, evidence accumulated for the last 2 decades is either contradictory (growth costs) or scant (immunological cost). Here, we experimentally test the existence of both costs in pied flycatcher (Ficedula hypoleuca) nestlings, a species in which parents appropriately respond to honest begging signals. Nestlings were paired by nest of origin and similar body mass. In each pair, a nestling was forced to beg for 51s/meal, whereas the other begged for only 3.4s/meal, both receiving the same amount of food. Simultaneously, the nestling immune response to an antigen (phytohemagglutinin) was measured. Experimental nestlings showed reduced immunocompetence compared with control chicks, which in this species could be regarded as a genuine direct cost. High-begging nestlings also gained less mass during the daylight activity hours. However, they lost less mass while resting at night, resulting in similar mass gains for both groups across the whole daily cycle. This suggests that negative effects of excess begging on mass gain can be compensated for by nestlings, thus avoiding the negative fitness consequences (i.e., cost) of a retarded growth. Mixed results found in previous studies may reflect interspecific differences in compensatory changes in mass gain. But if such differences do not map into fitness consequences, they may be of little help to answer the question of whether begging entails direct growth costs.

Effect of ambient noise on parent–offspring interactions in tree swallows

Many recent studies suggest that increased ambient noise can disrupt acoustic communication in animals and might ultimately decrease their reproductive success. Most of these studies have focused on long-distance signals used in mate attraction and territory defence, but close-range acoustic interactions between parents and offspring may also be disrupted by noise and are closely linked to reproductive success. To test the effect of noise on parent–offspring interactions, we experimentally applied white noise (65 dB SPL) to the nests of tree swallows, Tachycineta bicolor, when nestlings were 3–6 days old. At experimental nests, parents gave fewer provisioning calls, which are used to stimulate begging, but otherwise we detected no difference in provisioning behaviour between experimental and control nests. More nestlings begged for food at experimental nests, using calls that were higher in amplitude and minimum frequency, than at control nests. When we played back nestling begging calls during parental visits to stimulate higher feeding rates, parents increased their feeding rates at control nests, but not at experimental nests. Our results show that noise can alter parent–offspring interactions and interfere with parental responses to begging calls. Nestlings may be able to compensate for moderate increases in noise by enhancing the conspicuousness of their begging signal, although at higher noise levels these adjustments may prove ineffective or the extra begging effort may be physiologically costly.

Automated detection of honeybee begging signals from long term vibration monitoring of honeybee hives

We are using high performance accelerometers embedded in the honeycomb to create long term vibrational data sets comprising a range of individual bee pulsed vibrational messages. The statistics of the “vibrational language” of the honeybee can thus be explored. The aim of this study is to create and optimize software that detects and analyses the occurrences of honeybee “begging signals.” Recording from a beehive were monitored for 117 days (July to November 2014) from within its central frame using two ultra-high performance accelerometers (Bruel and Kjaer, 1000 mV/g), one in the center and the other one 7 cm lower down. Home-build Linux ‘bash code’ was written to continuously record the accelerometer output into separate one-hour long files, without any data loss. Matlab® code has been developed, that compares a template and instantaneous spectrograms to detect a begging signal. Six independent parameters of the template signal waveform were further optimized, in order to yield the maximum correct detections. Finally, the detection threshold was tuned ensuring that only begging signals were detected. The results show long term trends in the begging signal statistics, a breakthrough in exploring seasonal variations in the honeybee vibrational language.

Nest environment modulates begging behavior of a generalist brood parasite

In young birds, the intensity of the begging signal varies according to the chick’s internal condition (i.e., hunger or nutritional state) but may be additionally modulated by the external conditions experienced in the nest (e.g., nestmate competition or feeding success). Flexibility of begging in response to nest environment should be especially beneficial for the chicks of generalist brood parasites, which encounter diverse brood conditions depending on the host nest in which they are reared. We investigated variability in the begging behavior of an extreme generalist brood parasite, the shiny cowbird ( Molothrus bonariensis ). We compared visual and vocal begging variables of cowbird young of 5 days of age reared in nests of 2 common hosts, one smaller (house wren, Troglodytes aedon ) and one larger (chalk-browed mockingbird, Mimus saturninus ) than the parasite. Cowbird chicks were standardized for short-term hunger prior to recording and were similar in mass/condition in each host, but nevertheless begged more intensely in mockingbird than house wren nests, as indicated by increased stretching of the neck, lower latency to beg, increased time spent begging per bout and greater call rate. These results are consistent with young cowbirds adjusting their begging intensity based on the intrabrood competition of a given host, independent of need, an adaptability that likely contributes to their success as parasites utilizing diverse host species.

High begging intensity of great spotted cuckoo nestlings favours larger-size crow nest mates

In nests of birds parasitized by a larger non-evicting brood parasite, host chicks typically are at disadvantage in competing for food and often starve. However, when host chicks are larger, they may benefit from the presence of the parasite, which contributes to the net brood begging signal but cannot monopolize the food brought to the nest. Here, we show that, despite a higher begging intensity, great spotted cuckoos (Clamator glandarius) did not outcompete larger size carrion crow (Corvus corone corone) nestlings. Furthermore, cuckoos’ exaggerated begging allowed crow nest mates to decrease their begging intensity without negative consequences on food intake. Assuming an energetic cost to chicks of begging intensely, our results suggest that crow chicks sharing the nest with a cuckoo may obtain an advantage that should be weighed against the loss of indirect fitness due to parasitism.

Males respond to female begging signals of need: a handicapping experiment in the pied flycatcher, Ficedula hypoleuca

The ‘female nutrition’ hypothesis proposes that food provided by males during incubation is an important energy source for females in bird species in which females alone incubate. Females should be able to communicate their needs through begging signals to mates and males may compensate for the energetic limitations of females through their feeding visits, owing to their overlapping reproductive interests. To test whether female begging during incubation is an honest signal of energetic need and whether mates respond to it we experimentally handicapped female pied flycatchers at the beginning of incubation by clipping two primary flight feathers on each wing. Experimental manipulation led females to intensify begging displays arising from condition impairment and males accordingly increased their incubation feeding rates. Female begging intensity explained more than half of the variation in male incubation feeding rate, thereby showing that female nutrition is the main factor explaining male incubation feeding. Moreover, handicapped females consumed a higher proportion of male food deliveries during the first few days after hatching and weighed less at the end of the nestling period than control females. Handicapping had no influence on female incubation behaviour, hatching and breeding success, nestling and male condition or female nestling provisioning. The provisioning rates of males in the late nestling stage were higher in experimental nests. This is the first experimental study showing that males adjust incubation feeding rates to behavioural displays of need by their mates. The ability of females to modify their begging displays according to need may be an important adaptation that allows females to maintain a good energetic condition during incubation.