Acoustic parameters of begging calls indicate chick body condition in Wilson’s storm-petrels <Emphasis Type="Italic">Oceanites oceanicus</Emphasis>

Begging behaviour as a key element in the parent–offspring conflict has been studied in many avian species. These types of studies have nearly exclusively been based on call counts, and it is still not entirely clear whether begging calls themselves contain any information. We studied begging behaviour in Wilson’s storm-petrel Oceanites oceanicus, a small procellariiform seabird. This species provides the opportunity to study the signalling value of begging calls in the absence of potentially confounding factors such as nestling competition, previous feeding experiences and predation pressure. We applied a new method using a semi-automatic spectrogram analysis software that measures the acoustic parameters of begging calls. Our analysis revealed that the frequency parameters of begging calls reflect chicks’ current body condition, with chicks in poorer condition uttering calls at higher frequencies. Chicks uttering higher pitched calls also received larger meals. Our study shows that certain acoustic parameters of begging calls can indicate the state of a chick in Wilson’s storm-petrels.     

Hopeless solicitation? Host-absent vocalization in the common cuckoo has no effect on feeding rate of reed warblers

Begging behavior of nestlings can signal both hunger and competitive ability. Studies of begging in evicting avian brood parasites exclude the influence of nestling competition and may provide new insights into the host–parasite conflict and the evolution of signaling. Apart from the begging call, common cuckoo Cuculus canorus nestlings use special vocal displays in the absence of their hosts, termed here host-absent vocalization (HAV). Since these conspicuous calls can increase the risk of predation and require energy, their costs should be balanced by some benefits, such as increased food provisioning. However, there has been no evidence that chicks convey information about their hunger by HAV. We therefore tested experimentally whether cuckoo chicks use HAV as an additional signal to enhance food-delivery rate by their hosts. We used playback of HAV recorded from cuckoo nestlings to determine whether their hosts, reed warblers Acrocephalus scirpaceus, increase their provisioning in response to an apparent increase in HAV. Older chicks spent more time in HAV than younger chicks, suggesting that HAV is not caused by inaccurate discrimination of host arrival stimuli. Negative correlation of HAV with feeding rate and mass gain between the two experiments suggested that hunger was the motivation of HAV. The playback experiment, however, did not prove that HAV affects host provisioning rate. We discuss possible reasons for this result and provide alternative explanations for HAV, such as creating a bond between the hosts and the parasitic young used later in the postfledging care.     

Reliable Information Content and Ontogenetic Shift in Begging Calls of Grey Warbler Nestlings

The most critical assumption of communication models regarding parent–offspring conflict is that food solicitation displays of genetic offspring are honest signals to elicit beneficial parental care. A critical requirement of honesty is the reliable change of perceivable aspects of begging calls with physiological needs. We experimentally tested whether and how the acoustic structure and begging call rate of individual Grey Warbler Gerygone igata nestlings change with hunger level and age. We also examined a rarely documented component of chick begging calls, namely the temporal dynamics of acoustic modulation after nestlings heard parental feeding calls. Begging call structure narrowed in frequency range and, surprisingly, decreased in amplitude as chick hunger levels increased. We also found that begging calls changed with chick age, with the frequency increasing and the duration decreasing for older chicks. These results indicate that the acoustic properties of nestling Grey Warbler begging calls are complex and may be used to signal several aspects of nestling traits, including hunger level and age (or size, a correlate of age). Overall, begging calls of Grey Warbler chicks appear to be honest, implying that parents are likely to benefit from relying on the acoustic features of their progeny’s calls which predict chick need. Our results have important implications regarding the reliability and information content of nestling solicitation signals for the brood parasite shining cuckoo Chrysococcyx lucidus exploiting Grey Warbler parental care, in that these begging‐call mimetic specialist cuckoos might also need to match closely the dynamics of acoustic features of their host chicks’ calls.     

Parent-offspring conflict and the coordination of siblings in gulls

Offspring solicit food from their parents by begging behaviours. Studies on birds suggest that these displays are 'honest signals of need' and adults provide food according to the begging level. However, siblings may compete for parental resources and the begging intensity is expected to change with brood size. Here, we show that in the black-headed gull (Larus ridibundus) an increase of the numbers of siblings can result in a decrease of individual begging cost through nestlings' synchronized signalling. This is in accordance with some mathematical models. As parents respond to the total solicitation emerging from the nest, the probability to get food increases with the number of chicks begging together. The more siblings there are, the more they coordinate their begging while decreasing the number of individual begging bouts. Intra-brood synchronization of begging enables chicks to reduce their effort and hence exerting an important role in parental-offspring negotiation.     

Food restricted Tufted Puffin (Fratercula cirrhata) nestlings increase vocal activity during handling without modulating total or free corticosterone

In some species, corticosterone (CORT) appears to play a role in the control of begging behavior. Because of the potentially high costs associated with chronic elevation of CORT, it has also been proposed as a mechanism to ensure begging is an honest signal. We determined the effects of moderate food restriction (50% of high calorie treatment) on vocal behavior during handling, and on baseline levels of both total and ‘free’ unbound CORT in Tufted Puffin (Fratercula cirrhata) nestlings. Chick vocalizations during handling were similar to begging calls, and we assumed they were representative of begging behavior. We also measured total and free CORT in free-living Tufted Puffin chicks to determine if hormone levels in our experiment were comparable to natural levels. We found no effect of caloric restriction on either total or free baseline CORT, yet food-restricted nestlings vocalized more intensely during handling than chicks in the high calorie group. Mean plasma concentrations of total and free CORT in experimentally manipulated birds did not differ from levels in free-living nestlings. These results suggest that CORT does not play a role in modulating begging behavior in this species.     

Begging in the absence of sibling competition in Wilson’s storm-petrels, Oceanites oceanicus

Begging displays of nestlings in multichick broods can signal both hunger and competitive ability. Studies of begging in species with single-chick broods exclude the influence of nestling competition and may provide especially useful models for the study of signalling during parent-offspring conflict. However, there is no evidence that chicks signal hunger by begging in the absence of sibling competition. I tested predictions of signalling models in a species with single-chick broods, the Wilson's storm-petrel. Chicks used two types of begging calls, ‘rhythmic’ calls and ‘long’ calls. I found that chicks conveyed information about their current body condition by begging. When their body condition was low, chicks increased the number and frequency of long begging calls, as well as the frequency of rhythmic calling. Parents responded to increased begging by regurgitating larger meals. The study thus demonstrates that the begging system can work in the absence of nestling competition. Chicks also called in the absence of their parents, but in this context they used only rhythmic calls and there was no correlation with current body condition. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Shared parental care is costly for nestlings of common cuckoos and their great reed warbler hosts

Obligate avian brood parasitism typically involves one of 2strategies: parasite chicks are either 1) virulent and evictall other eggs and nest mates to be raised alone or 2) moretolerant and share foster parental care with host chicks forsome or the entirety of the nestling period. We studied theconsequences of experimentally forced mixed broods of age-matchedone common cuckoo (Cuculus canorus) and 2 great reed warbler(Acrocephalus arundinaceus) chicks. In these broods, both cuckooand host chicks grew slower than did either individual cuckoosor great reed warblers in broods of 1 parasite or 3 host chicks,respectively. Video records showed that in mixed broods, cuckoochicks received feedings less frequently than the 33% predictedby chance at 4 days of age but parental food allocations increasedto chance levels at 8 days of age. The consistent patterns oflower growth rates arose even though chicks in broods of 1 parasiteand 2 hosts received the largest prey items per feeding. Inaddition, several other measures of parental provisioning alsodid not predict species and brood-specific differences in nestlinggrowth rates across the different treatments. However, variationin begging displays and its specific costs on host and parasitechicks in the different nest treatments were not quantifiedin this study. We conclude that young of nest mate–evictorcommon cuckoos benefit from the sole occupancy of host nestsin part owing to an initial competitive disadvantage for parentalcare in broods with age-matched great reed warbler chicks.     

Complementarity effects through dietary mixing enhance the performance of a generalist insect herbivore

The ontogenetic niche concept predicts that resource use depends on an organism’s developmental stage. This concept has been investigated primarily in animals that show differing resource use strategies as juveniles and as adults, such as amphibians. We studied resource use and performance in the grasshopper Chorthippus parallelus (Orthoptera, Acrididae) provided with food plant mixtures of either one, three or eight plant species throughout their development. C. parallelus survival and fecundity was highest in the food plant mixture with eight plant species and lowest in the treatments where only one single plant species was offered as food. C. parallelus’ consumption throughout its ontogeny depended on sex, and feeding on different plant species was dependent on a grasshopper’s developmental stage. To depict grasshopper foraging in food plant mixtures compared to foraging on single plant species, we introduce the term “relative forage total” (RFT) based on an approach used in biodiversity research by Loreau and Hector (Nature 413:548–274, 2001). RFT of grasshoppers in food plant mixtures was always higher than what would have been expected from foraging in monocultures. The increase in food consumption was due to an overall increase in feeding on plant species in mixtures compared to consumption of the same species offered as a single diet. Thus we argue that grasshopper foraging exhibits complementarity effects. Our results reinforce the necessity to consider development-related changes in insect herbivore feeding. Thorough information on the feeding ontogeny of insect herbivores could not only elucidate their nutritional ecology but also help to shed light on their functional role in plant communities. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Begging behaviour of nestlings and food delivery by parents: the importance of breeding strategy

Studies of begging behaviour and food provisioning have produced contradictory results. Here, I present a new idea that may explain these apparent contradictions based on the fact that in species with brood reduction (brood reducers) some chicks starve, but in species that adjust clutch size (clutch adjusters) all chicks typically survive to fledge. This suggests that parents adopting these different strategies may follow different provisioning rules. In clutch adjusters, parents tend to distribute food equitably among their chicks, preferentially feeding young that are in poorer condition, but in brood reducers parents selectively feed larger chicks independently of begging intensity. Received in revised form: 27 March 2001 Electronic Publication     

Responses of breeding Cory's shearwater Calonectris diomedea to experimental manipulation of chick condition

We studied the regulation of provisioning in Cory's shearwaterat Selvagem Grande during the chick rearing period. Provisioningwas examined in terms of feeding frequency and amount of fooddelivered to chicks. Two groups of chicks were subjected toshort-term contrasting manipulations of their nutritional status:one group of chicks was given a food supplement of about 30g, and another group was deprived of up to 30 g of food. Adultstending deprived chicks increased the frequency of feedingvisits (but not the size of feeds), which resulted in an increasein the net rate of food delivery. At the end of this study,deprived chicks were growing at the same rate as fed chicks. Parents attending fed chick did not change their provisioningrates in response to the treatment. Our results indicate thatCory's shearwaters are able to adjust their provisioning ratein response to short-term variation in the nutritional statusof their chicks. We also examined the change in the beggingrate of fed and deprived chicks in response to the treatment.There was no relationship between the begging rate and thecondition of chicks, which is taken to be a measure of thechick's physiological condition, related to its ability towithstand imposed periods of fasting. However, fed chicks decreasedtheir begging rate after the increase in their condition dueto supplementary food. Conversely, deprived chicks, which wereonly able to sustain their condition before the onset of thetreatment, maintained high levels of begging. To some extent,these results suggest that parental provisioning can be influencedby the begging behavior of chicks.     

Context-dependent honest begging in Cory’s shearwaters (<Emphasis Type="Italic">Calonectris diomedea</Emphasis>): influence of food availability

A key question in parent-offspring conflict is if provisioning is controlled primarily by parents or by their offspring, and how this interaction is mediated behaviourally. We recorded the vocalisations of chicks of Corys shearwater (Calonectris diomedea) during feeding sessions in a season with abundant food. Corys shearwater chicks conveyed information about their body condition through begging, and parents were responsive to the level of solicitation. In order to test experimentally for the effects of saturation on begging, we supplemented chicks food. Observational and experimental data both indicated that satiated chicks did not beg, and consequently no feeding occurred. Adults decreased their attendance following the decreased demand of supplemented chicks. We compare the results with data from a poor breeding season. The data suggest that only during the good season was variation in begging large enough to be detected and to serve as a reliable signal to the parents. Our results are in line with the predictions of a recent model indicating that begging signals were most informative to the parents in a context when there was a class of satiated individuals which stand to gain no benefit from the resource (and hence will refrain from signalling).     

Imperfect mimicry of host begging calls by a brood parasitic cuckoo: a cue for nestling rejection by hosts?

Coevolutionary interactions between avian brood parasites and their hosts often lead to the evolution of discrimination and rejection of parasite eggs or chicks by hosts based on visual cues, and the evolution of visual mimicry of host eggs or chicks by brood parasites. Hosts may also base rejection of brood parasite nestlings on vocal cues, which would in turn select for mimicry of host begging calls in brood parasite chicks. In cuckoos that exploit multiple hosts with different begging calls, call structure may be plastic, allowing nestlings to modify their calls to match those of their various hosts, or fixed, in which case we would predict either imperfect mimicry or divergence of the species into host-specific lineages. In our study of the little bronze-cuckoo (LBC) Chalcites minutillus and its primary host, the large-billed gerygone Gerygone magnirostris, we tested whether: (1) hosts use nestling vocalizations as a cue to discriminate cuckoo chicks; (2) cuckoo nestlings mimic the host begging calls throughout the nestling period; and (3) the cuckoo begging calls are plastic, thereby facilitating mimicry of the calls of different hosts. We found that the begging calls of LBCs are most similar to their gerygone hosts shortly after hatching (when rejection by hosts typically occurs) but become less similar as cuckoo chicks get older. Begging call structure may be used as a cue for rejection by hosts, and these results are consistent with gerygone defenses selecting for age-specific vocal mimicry in cuckoo chicks. We found no evidence that LBC begging calls were plastic.     

Positive diversifying selection in avian Mx genes

Mx proteins are interferon-induced GTPases that confer antiviral activities against RNA viruses. We analysed the molecular evolution of the Mx gene in birds using data on interspecific divergence in anseriform and galliform birds, and on intraspecific diversity in commercial chicken lines, local Chinese chicken breeds as well as in the mallard. The overall ratio of non-synonymous to synonymous substitution was unusually high, 0.80, indicating relaxed constraint or positive selection. Evidence for the latter was provided by that a total of 11–18 codons were found to have evolved under positive selection. The great majority of these codons are located in a region unique to birds at the N-terminal end of the Mx protein. We found an excess of non-synonymous polymorphisms relative to synonymous variants in all comparisons. This, together with positive Tajima’s D values in the local Chinese chicken breeds and in the mallard suggests that balancing selection is acting in avian Mx genes. As such, Mx mimics the major histocompatibility complex system, indicating that heterozygous individuals are better off withstanding pathogen attack. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. S.B. and L.Q. contributed equally to this work.     

Darwin's Finch Begging Intensity Does Not Honestly Signal Need in Parasitised Nests

Parental care should be selected to respond to honest cues that increase offspring survival. When offspring are parasitised, the parental food compensation hypothesis predicts that parents can provision extra food to compensate for energy loss due to parasitism. Chick begging behaviour is a possible mechanism to solicit increased feeding from attending parents. We experimentally manipulated parasite intensity from Philornis downsi in nests of Darwin's small ground finch (Geospiza fuliginosa) to test its effects on chick begging intensity and parental food provisioning. We used in‐nest video recordings of individually marked chicks to quantify nocturnal parasite feeding on chicks, subsequent diurnal chick begging intensity and parental feeding care. Our video analysis showed that one chick per brood had the highest parasite intensity during the night (supporting the tasty chick hypothesis) and weakest begging intensity during the day, which correlated with low parental care and rapid death. We observed sequential chick death on different days rather than total brood loss on a given day. Our within‐nest video images showed that (1) high nocturnal larval feeding correlated with low diurnal begging intensity and (2) parent birds ignored weakly begging chicks and provisioned strongly begging chicks. Excluding predation, all parasite‐free chicks survived (100% survival) and all parasitised chicks died in the nest (100% mortality). Weak begging intensity in parasitised chicks, which honestly signalled recent parasite attack, was not used as a cue for parental provisioning. Parents consistently responded to the strongest chick in both parasitised and parasite‐free nests.     

Chick begging as a signal: are nestlings honest?

Begging by dependent avian offspring is known to correlate withhunger level, and parents use this as a signal of brood demandto adjust their chick feeding behavior. While there is informationon how each chick adjusts its begging to its own condition,little is known of how chicks adjust to the state of their nestmates. In two experiments we manipulated the competitive environmentof individual European starling (Sturnus vulgaris) chicks byaltering the state of nest mates while holding the state oftarget chicks constant In the first experiment we placed thetarget chick's nest mates in neighboring nests with brood sizesof two, five, or eight chicks. Following the manipulation wereturned them to their own nests and recorded begging behavioron videotape. In the second experiment we separated a targetchick from its siblings and manipulated feeding level in thelaboratory. The siblings were fed at one of three levels; meanwhile,all the target chicks were fed at the intermediate level. Afterthe manipulation we placed the target chicks with their siblingsand recorded their begging in response to an artificial stimulus.In neither experiment was the begging effort of the unmanipulatedtarget chicks affected by the changes in begging behavior oftheir siblings. This result supports the view that begging isa reliable signal of individual chick state and does not involveresponses to the effort of nest mates.     

Contact Density Affects Protein Evolutionary Rate from Bacteria to Animals

The density of contacts or the fraction of buried sites in a protein structure is thought to be related to a protein’s designability, and genes encoding more designable proteins should evolve faster than other genes. Several recent studies have tested this hypothesis but have found conflicting results. Here, we investigate how a gene’s evolutionary rate is affected by its protein’s contact density, considering the four species Escherichia coli, Saccharomyces cerevisiae, Drosophila melanogaster, and Homo sapiens. We find for all four species that contact density correlates positively with evolutionary rate, and that these correlations do not seem to be confounded by gene expression level. The strength of this signal, however, varies widely among species. We also study the effect of contact density on domain evolution in multidomain proteins and find that a domain’s contact density influences the domain’s evolutionary rate. Within the same protein, a domain with higher contact density tends to evolve faster than a domain with lower contact density. Our study provides evidence that contact density can increase evolutionary rates, and that it acts similarly on the level of entire proteins and of individual protein domains. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nestling competition,rather than supernormal stimulus,explains the success of parasitic brown-headed cowbird chicks in yellow warbler nests

Interspecific parasitic chicks are usually fed more than the smaller host young with whom they share the nest. This could be due to parasitic chicks having evolved exaggerated features that are preferred by the adults to the features present in their own young (the supernormal stimulus hypothesis). Alternatively, the success of parasitic chicks could be due to them being better competitors. We tested these hypotheses by studying the interaction between brown-headed cowbird chicks, Molothrus ater, and a common small host, the yellow warbler, Dendroica petechia. Parasitic chicks begged more intensively than the host''s young and received most of the feeds. The relative height reached by the begging chicks of both species was the most important variable in determining their feeding success. Being larger and begging intensively, brown-headed cowbirds were better able to reach higher than the host''s young, but at equal heights parasitic chicks were no better than the host''s young at gaining feeds. It is suggested that the success of the brown-headed cowbirds when parasitizing yellow warblers is due to them physically out-competing the smaller young of their hosts, and not to them evoking a stronger response from the hosts by being a supernormal stimulus.     

Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators

Nest predation is a major source of reproductive failure in birds and thus it can exert selection on both parental and offspring strategies. Begging calls are known to be a powerful component of parent–offspring communication but these calls can also increase predation risk. Here we demonstrate a sophisticated strategy for the development of begging vocalization in a species under high nest predation. Blackcap Sylvia atricapilla nestlings spend most of their nesting period silent, and develop begging calls just before they are able to fledge. The onset of begging vocalization matches the onset of endothermy, which enables Blackcap chicks to leave the nest. We demonstrate experimentally that begging calls function as a signal of the increased needs of homeothermic nestlings. Playback of begging calls conducted in nests with silent nestlings resulted in a significant increase in feeding rates and a decrease in brooding. Development of begging calls only at the age of endothermy allows species under high nest predation to keep the risky period of begging vocalizations and frequent feeding to a minimum. This strategy may constitute an evolutionary solution to high predation pressure in some open nesting passerines. This is the first study to demonstrate the existence of silent begging in a passerine.     

Nest‐dwelling ectoparasites reduce begging effort in Pied Flycatcher Ficedula hypoleuca nestlings

Parasitized nestlings might be expected to increase begging effort to obtain additional resources to compensate for those sequestered by their parasites. However, begging is costly and chicks harbouring parasites may find it more difficult to attain high begging levels. Consequently, we predicted that, for the same level of nutritional need, nestlings that are parasitized will invest less in begging than those that are not parasitized. We tested this prediction by measuring begging in Pied Flycatcher Ficedula hypoleuca nestlings parasitized with haematophagous mites Dermanyssus gallinoides and Dermanyssus gallinae and blowfly larvae Protocalliphora azurea, and subjected to different levels of food deprivation in order to control for short‐term nutritional need. Nestlings from nests with ectoparasites spent less time begging than those from nests without parasites, especially when very hungry, although there was no association with latency to beg or begging intensity. Our results suggest that time invested in begging may indicate not only the level of need, but also nestling parasitism status.     

Coevolutionary dynamics of adaptive radiation for food-web development

To investigate how complex food-webs can develop through repeated evolutionary diversification, a predator–prey model was analyzed. In the model, each individual has two traits: trait x as a predator and trait y as a prey. These traits constitute a two-dimensional phenotype space, in which the whole group of individuals are represented as a phenotype distribution. Predator–prey interactions among the phenotypes are determined by their relative positions in the phenotype space. Each phenotypic cluster was treated as a species. Each species evolves in y to escape from predation, while it evolves in x to chase their prey. Analytical investigation provided two predictions. First, coupled evolutionary diversifications of y and x may occur when the x of predators have caught up with their prey’s y, which may be repeated. Second, complex food-webs may develop when species’ competitive strengths are kept similar within the communities. If the functional response is close to the ratio-dependent response, the competitive strengths of all species are similar when the relationship between predators and prey corresponds to the ideal free distribution (IFD). These predictions were confirmed by numerical simulations. Electronic supplementary material  The online version of this article doi:() contains supplementary material, which is available to authorized users.