Nest mate size, but not short-term need, influences begging behavior of a generalist brood parasite

Hosts of generalist brood parasites often vary with regardsto their life-history traits, and these differences have thepotential to influence the competitive environment experiencedby brood-parasitic nestlings. Although begging by brood parasitesis more exaggerated than their hosts, it is unclear if generalistbrood parasites modulate their begging behavior relative tohost size. I examined the begging behavior of brown-headed cowbird(Molothrus ater) nestlings when competing against nest matesthat differ in size and under different levels of short-termneed. Cowbird nestlings begged on nearly all feeding visits,responded to adults as fast as (or faster than) their nest mates,and typically begged more intensively than their nest mates.Latency to beg, time spent begging, and maximum begging postureof cowbirds were similar during supplementation and deprivationtreatments, indicating begging intensity was not influencedby short-term need. Time spent begging by cowbirds varied amonghosts of 3 different sizes when short-term need was standardized,suggesting that nest mate size strongly influenced begging behavior.Cowbirds obtained more food when competing against an intermediate-sizedhost due to lower provisioning rates of small hosts or becauseof increased competitive ability of large host nestlings. Overall,cowbirds obtained the greatest volume of food per unit timespent begging when competing against intermediate hosts, butthis value approached that of the small host when adjusted formodal brood size. These results demonstrate that cowbirds adjusttheir begging relative to the size of the hosts against whichthey compete but not to levels of short-term need.     

Egg puncture allows shiny cowbirds to assess host egg development and suitability for parasitism

Parasitic cowbirds and cuckoos generally reduce the clutch size of the hosts they parasitize by removing or destroying some of their eggs. Shiny cowbirds (Molothrus bonariensis) puncture their hosts'' eggs both when parasitizing the nests and also when they do not parasitize them. We propose that, by puncturing the host''s eggs, shiny cowbirds gain an informational benefit. They assess the degree of development of the host''s embryos and so avoid laying in nests that would not provide enough incubation time for the parasitic eggs to hatch. Two predictions follow: (i) punctures should occur in advance or immediately before parasitic events, and (ii) the occurrence of parasitism should depend on the degree of development of the host''s embryos when punctures occurred, i.e. on the stage of incubation. Both predictions are supported by our data of shiny cowbirds parasitizing yellow-winged blackbirds (Agelaius thilius). Egg punctures are not used to reset the host''s nesting attempt when shiny cowbirds do not parasitize the nests. We discuss the potential mechanisms implicated in egg development assessment and propose a critical experiment to test this hypothesis.     

Nestling cuckoos,Cuculus canorus,exploit hosts with begging calls that mimic a brood

Nestling cuckoos, Cuculus canorus, eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus, as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula, or song thrush, T. philomelos, chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick''s rapid begging call (''si, si, si, si ...''), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.     

How selfish is a cowbird nestling?

Brood-parasitic young are reared in the nests of different species and can derive no genetic benefit from the survival of host offspring. However, although the nestlings of many parasitic cuckoo and honeyguide species routinely kill host young soon after hatching, nestling brown-headed cowbirds, Molothrus ater, tolerate host offspring and are commonly reared alongside them for at least part of the nestling period. I used comparative analyses of data from the literature to investigate whether brown-headed cowbird nestlings gain direct benefits by allowing host young to live. The brown-headed cowbird (44 g) parasitizes many passerines (adult mass range about 5-90 g) and the likelihood that host young survive to fledge from parasitized nests varies between species. In common with previous work, I found that host offspring mortality was highest in species whose offspring were relatively small compared with the cowbird nestling. Furthermore, cowbird nestlings were most likely to fledge when reared alongside host young of intermediate size. In these nests, one or two host young typically fledged as well. I suggest that cowbirds, and other host-tolerant brood parasites, could benefit from the presence of host nestlings through the assistance that host chicks offer in soliciting a higher provisioning rate, and that such benefits might outweigh the costs of having competition for food at each nest visit. Variation in this cost-benefit ratio could explain differences between brood parasite species in their tolerance of host young.     

Honesty in host-parasite communication signals: the case for begging by fledgling brown-headed cowbirds Molothrus ater

Nestling parasites typically beg more intensively than do host nestlings yet these exaggerated displays are also honest in that they are modulated by hunger and age. We hypothesized that honesty was also maintained in the food solicitation behaviors of fledgling brood parasites because the benefits and costs of their begging displays are similar to those of nestling parasites. Begging displays of hand-reared 14–32 days old brown-headed cowbirds Molothrus ater that had experimentally manipulated nutritional needs were recorded to analyze variation in the peak frequency, duration, and rate of fledglings' begging bouts. Peak frequency of bouts decreased with greater age and was lower for females. Bout rate was greater with increasing hunger levels of fledgling parasites but did not vary with age. Consistent and predictable variation of acoustic begging displays with age, sex, and hunger-level indicates honesty in host-parasite communication systems through conveying truthful information about the many possible needs of parasitic fledglings.     

Genetic analysis of brown-headed cowbirds Molothrus ater raised by different hosts: data from mtDNA and microsatellite DNA markers

Ecological and behavioural data suggest that female brood parasitic brown-headed cowbirds Molothrus ater are host generalists; this predicts that there should be no genetically differentiated host races within cowbird populations. We tested this hypothesis by comparing differentiation in two rapidly evolving DNA markers (mtDNA control region sequence and nuclear DNA microsatellite loci) among unrelated cowbird chicks raised by two ecologically distinct hosts. No differentiation was observed in either marker supporting the absence of host race hypothesis.     

Comparative hatching characteristics of nonparasitic and parasitic icterids: is the hatching of cowbird young constrained by an unusually thick eggshell?

Studies of avian brood parasitism have provided some of the best evidence of coevolutionary arms races. One of the parasitic adaptations exhibited by cuckoos (family Cuculidae) and cowbirds (family Icteridae) is the development of a thick eggshell, presumably to avoid damage from puncture ejection by some hosts and/or accidental damage during egg-laying in the host nest. However, it is unknown whether this trait constrains the hatching of parasitic young. The differences in hatching characteristics between the host red-winged blackbird (“redwing;” Agelaius phoeniceus) and the parasitic brown-headed cowbird (Molothrus ater) were examined. Prehatched cowbird young were found to spend more time hatching than pre-hatched redwing young and to emit click sounds at a greater rate in relation to pulmonary respiration than pre-hatched redwing young. However, cowbird hatchlings appear to have evolved other hatching-related traits that may compensate for the greater hatching effort, such as body parts and an egg tooth that are relatively large compared with those of redwing hatchlings.     

Hatching asynchrony, nestling competition, and the cost of interspecific brood parasitism

All parental hosts of heterospecific brood parasites must paythe cost of rearing non-kin. Previous research on nest parasitismby brown-headed cowbirds (Molothrus ater) concluded that competitivesuperiority of the typically more intensively begging and largercowbird chick leads to preferential feeding by foster parentsand causes a reduction in the hosts' own brood. The larger sizeof cowbird nestlings can be the result of at least two causes:(1) cowbirds preferentially parasitize species with smallernestlings and lower growth rates; and/or (2) cowbirds hatchearlier than hosts. I estimated the cost of cowbird parasitismfor each of 29 species by calculating the difference betweenhosts' published brood sizes in nonparasitized and parasitizednests and using clutch size to standardize values. In this analysis,greater incubation length and lower adult mass, surrogate measuresof the hatching asynchrony and size difference between parasiteand hosts, were both related to greater costs of cowbird parasitismwithout bias owing to phylogeny. To establish causality, I manipulatedclutch contents of eastern phoebes (Sayornis phoebe) and examinedwhether earlier hatching by a single cowbird or phoebe egg reducesthe size of the rest of the original host brood. As predicted,greater hatching asynchrony increased the proportion of theoriginal phoebe brood that was lost. This measure of the costof parasitism was partially owing to increased hatching failureof the original eggs in asynchronous broods but was not at allrelated to the size differences of older and younger conspecificnestmates. However, proportional brood loss owing to an earlierhatching conspecific was consistently smaller than brood lossowing to asynchronous cowbirds in both naturally and experimentallyparasitized phoebe nests. These results imply that althoughhatching asynchrony is an important cause of the reduction ofhost broods in parasitized clutches, competitive features ofcowbird nestlings remain necessary to explain the full extentof hosts' reproductive costs caused by interspecific brood parasitism.     

Shiny Cowbird parasitism of a low quality host: effect of host traits on a parasite's reproductive success

ABSTRACT.   The reproductive success of parasitic cowbirds ( Molothrus spp.) varies among host species and is influenced by the degree of synchronization in timing of egg laying, the duration of parasite and host incubation periods, and the ability of hosts to incubate and rear parasite young. We studied the reproductive success of Shiny Cowbirds ( Molothrus bonariensis ) that parasitized the nests of Creamy-bellied Thrushes ( Turdus amaurochalinus ) in the Monte desert region of Argentina. Shiny Cowbirds frequently parasitized Creamy-bellied Thrush nests (60%), and most cowbirds synchronized egg laying with that of thrushes (79%). Most parasitic eggs (80%) hatched within 1 d of the hatching of the first host egg, and more than 91% of the eggs survived until the end of the incubation. However, only 60% of the cowbird eggs hatched and 52% of young survived. The proportion of Shiny Cowbirds eggs laid in Creamy-bellied Thrush nests that resulted in fledged young was 0.03, including eggs and young lost due to predation or desertion. Despite this low reproductive success, Creamy-bellied Thrushes were heavily parasitized by Shiny Cowbirds in our study area. Shiny Cowbirds may continue to parasitize these thrushes because of diffuse selection or because Shiny Cowbird chicks are more likely to fledge from Creamy-bellied Thrush nests in years or areas with greater food availability when brood reduction does not occur.     

Do Hosts Discriminate between Sexually Dichromatic Male and Female Brown‐headed Cowbirds?

Female brood parasites are recognized as threats to reproductive success by many host species. Male brood parasites may accompany females while they search for nests to parasitize and males depredate nests throughout the nesting cycle. Hence, selection may also favour recognition of males. We examined whether two common host species perceive male brown-headed cowbirds ( Molothrus ater ) as brood parasites, as nest predators, or neither. We quantified visits of male cowbirds to nests of yellow warblers ( Dendroica petechia ) and red-winged blackbirds ( Ageliaus phoeniceus ) to assess the frequency with which these host species interact with male cowbirds. Males were observed near nests during hosts' laying and incubating stages, although less frequently than female cowbirds. No visits by cowbirds occurred while parents cared for nestlings. We then presented models of male and female cowbirds plus a non-threatening control to yellow warblers and red-winged blackbirds during laying and nestling periods. If hosts perceive males and females similarly, they should respond more intensely to the cowbird models during the laying period, when nests are most likely to be parasitized. Both species responded similarly to male and female cowbird models during laying, which suggests that hosts view cowbirds of both sexes as threats. The responses of yellow warblers with nestlings to male cowbirds were strongly influenced by the order of model presentation. Warblers first presented with the male cowbird gave much reduced anti-parasite responses than those that first interacted with the female then the male cowbird. These results suggest that yellow warblers recognized male vs. female cowbirds, but that discrimination was not expressed during laying. By contrast, red-winged blackbirds did not discriminate between male and female cowbirds at either nesting stage.     

Differences in the nestling begging calls of hosts and host-races of the common cuckoo, Cuculus canorus

We compared nestling begging calls of four hosts (reed warbler, Acrocephalus scirpaceus; great reed warbler, A. arundinaceus; dunnock, Prunella modularis; and meadow pipit, Anthus pratensis) and the respective host-races of the common cuckoo. Note structure varied between host species, but not between cuckoo host-races, so cuckoos did not vary their call note structure to match that of their hosts' chicks. Call rate increased with age, but there were marked differences between both host species and cuckoo host-races. Dunnock-cuckoos called more rapidly than reed warbler-cuckoos despite growing at the same rate. We suggest this difference reflects how cuckoos tune into the way these host species respond to begging signals from their own young, because dunnock chicks called much more rapidly than reed warbler chicks. Great reed warbler-cuckoos called at a lower rate than reed warbler-cuckoos when young, but at a greater rate when older than 8 days. This could also result from the cuckoo chicks tuning into differences in the way these hosts respond to begging signals. However, great reed warbler-cuckoos grew at a faster rate than the other cuckoo host-races, so they may also call faster to demand higher provisioning rates from this larger host. To test these hypotheses critically, data are needed on how the different host species integrate visual and vocal begging signals from their own broods. We discuss how differences in cuckoo begging might develop, given that cuckoo host-races are restricted to female cuckoo lineages. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Community-level patterns of population recruitment in a generalist avian brood parasite, the brown-headed cowbird

The brown-headed cowbird (Molothrus ater) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare cowbird egg investment and recruitment among host species; (3) identify host species of most importance to cowbird recruitment. Cowbirds parasitized 11 host species, with five “major” hosts experiencing high parasitism levels (≥1 cowbird egg/nest) and six minor hosts experiencing low parasitism levels (<0.3 cowbird eggs/nest). Parasitism level was not correlated with host species abundance, host mass, host nestling period length, or host success at fledging cowbirds. However, tree-nesting hosts were parasitized more than ground-nesters, and foliage-gleaners more than sally-foragers and ground-foragers. Average estimated survival to fledging of cowbird eggs laid in active host nests was 0.19. Cowbird recruitment was diverse with respect to hosts but was less evenly distributed across the host community than was cowbird egg investment because western tanagers (Piranga ludovicianus) fledged cowbirds more successfully than other hosts. This success in western tanagers was due to high cowbird survivorship in tanager nests and may be associated with the larger body size of tanagers relative to other hosts.     

Differential reproductive success favours strong host preference in a highly specialized brood parasite

Obligate avian brood parasites show dramatic variation in the degree to which they are host specialists or host generalists. The screaming cowbird Molothrus rufoaxillaris is one of the most specialized brood parasites, using a single host, the bay-winged cowbird (Agelaioides badius) over most of its range. Coevolutionary theory predicts increasing host specificity the longer the parasite interacts with a particular avian community, as hosts evolve defences that the parasite cannot counteract. According to this view, host specificity can be maintained if screaming cowbirds avoid parasitizing potentially suitable hosts that have developed effective defences against parasitic females or eggs. Specialization may also be favoured, even in the absence of host defences, if the parasite's reproductive success in alternative hosts is lower than that in the main host. We experimentally tested these hypotheses using as alternative hosts two suitable but unparasitized species: house wrens (Troglodytes aedon) and chalk-browed mockingbirds (Mimus saturninus). We assessed host defences against parasitic females and eggs, and reproductive success of the parasite in current and alternative hosts. Alternative hosts did not discriminate against screaming cowbird females or eggs. Egg survival and hatching success were similarly high in current and alternative hosts, but the survival of parasitic chicks was significantly lower in alternative hosts. Our results indicate that screaming cowbirds have the potential to colonize novel hosts, but higher reproductive success in the current host may favour host fidelity.     

Experimental Shifts in Intraclutch Egg Color Variation Do Not Affect Egg Rejection in a Host of a Non-Egg-Mimetic Avian Brood Parasite

Avian brood parasites lay their eggs in the nests of other birds, and impose the costs associated with rearing parasitic young onto these hosts. Many hosts of brood parasites defend against parasitism by removing foreign eggs from the nest. In systems where parasitic eggs mimic host eggs in coloration and patterning, extensive intraclutch variation in egg appearances may impair the host’s ability to recognize and reject parasitic eggs, but experimental investigation of this effect has produced conflicting results. The cognitive mechanism by which hosts recognize parasitic eggs may vary across brood parasite hosts, and this may explain variation in experimental outcome across studies investigating egg rejection in hosts of egg-mimicking brood parasites. In contrast, for hosts of non-egg-mimetic parasites, intraclutch egg color variation is not predicted to co-vary with foreign egg rejection, irrespective of cognitive mechanism. Here we tested for effects of intraclutch egg color variation in a host of nonmimetic brood parasite by manipulating egg color in American robins (Turdus migratorius), hosts of brown-headed cowbirds (Molothrus ater). We recorded robins’ behavioral responses to simulated cowbird parasitism in nests where color variation was artificially enhanced or reduced. We also quantified egg color variation within and between unmanipulated robin clutches as perceived by robins themselves using spectrophotometric measures and avian visual modeling. In unmanipulated nests, egg color varied more between than within robin clutches. As predicted, however, manipulation of color variation did not affect rejection rates. Overall, our results best support the scenario wherein egg rejection is the outcome of selective pressure by a nonmimetic brood parasite, because robins are efficient rejecters of foreign eggs, irrespective of the color variation within their own clutch.     

Does nesting habitat predict hatch synchrony between brood parasitic brown‐headed cowbirds Molothrus ater and two host species?

Nestling brown-headed cowbirds Molothrus ater typically hatch earlier and grow faster than young of the many host species of this generalist obligate brood parasite. However, a cowbird chick also benefits from the presence of some host nest mates as the parasite is provisioned disproportionately more with increasing brood size. Since asynchronous hatching affects both cowbird and host nestlings' growth and survival, mechanisms that optimize the timing of egg-laying by female parasites should be prevalent. Several habitat features might facilitate optimal timing of parasitic egg-laying and we examined whether aspects of host nesting habitat predicted cowbird hatching synchrony. We tested whether synchronous nests were less concealed, closer to perches, and located in areas of higher host density than asynchronous nests using a broad-scale information theoretic approach. There was no support for these predictions regarding song sparrow ( Melospiza melodia ; n=55) or yellow warbler ( Dendroica petechia ; n=67) nests parasitized by brown-headed cowbirds at Mono Lake, USA. For example, the best statistical models for predicting hatching synchrony in yellow warbler nests included nesting-patch width and nest-substrate shrub species. However, these relationships were relatively weak: both synchronous and asynchronous nests were in patches with statistically indistinguishable widths and the two dominant shrub species at our site contained similar proportions of synchronous and asynchronous nests. We conclude that the variability of host nesting habitats does not contribute to a biologically consistent effect on hatching synchrony by this generalist brood parasite.     

A generalist brood parasite modifies use of a host in response to reproductive success

Avian obligate brood parasites, which rely solely on hosts to raise their young, should choose the highest quality hosts to maximize reproductive output. Brown-headed cowbirds (Molothrus ater) are extreme host generalists, yet female cowbirds could use information based on past reproductive outcomes to make egg-laying decisions thus minimizing fitness costs associated with parasitizing low-quality hosts. We use a long-term (21 years) nest-box study of a single host, the prothonotary warbler (Protonotaria citrea), to show that local cowbird reproductive success, but not host reproductive success, was positively correlated with the probability of parasitism the following year. Experimental manipulations of cowbird success corroborated that female cowbirds make future decisions about which hosts to use based on information pertaining to past cowbird success, both within and between years. The within-year pattern, in particular, points to local cowbird females selecting hosts based on past reproductive outcomes. This, coupled with high site fidelity of female cowbirds between years, points to information use, rather than cowbird natal returns alone, increasing parasitism rates on highly productive sites between years.     

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

Egg mimicry by obligate avian brood parasites and host rejection of non-mimetic eggs are well-known textbook examples of host-parasite coevolution. By contrast, reciprocal adaptations and counteradaptations beyond the egg stage in brood parasites and their hosts have received less attention. The screaming cowbird (Molothrus rufoaxillaris) is a specialist obligate brood parasite whose fledglings look identical to those of its primary host, the baywing (Agelaioides badius). Such a resemblance has been proposed as an adaptation in response to host discrimination against odd-looking young, but evidence supporting this idea is scarce. Here, we examined this hypothesis by comparing the survival rates of young screaming cowbirds and non-mimetic shiny cowbirds (Molothrus bonariensis) cross-fostered to baywing nests and quantifying the similarity in plumage colour and begging calls between host and cowbird fledglings. Shiny cowbirds suffered higher post-fledging mortality rates (83%) than screaming cowbirds (0%) owing to host rejection. Visual modelling revealed that screaming cowbirds, but not shiny cowbirds, were indistinguishable from host young in plumage colour. Similarly, screaming cowbirds matched baywings' begging calls more closely than shiny cowbirds. Our results strongly support the occurrence of host fledgling mimicry in screaming cowbirds and suggest a role of visual and vocal cues in fledgling discrimination by baywings.     

Phylogenetic analysis of life-history adaptations in parasitic cowbirds

Parasitic cowbirds lay eggs in the nests of other species anddupe them into caring for their young. Unlike other brood parasites,cowbirds have not developed egg mimicry or bizarre chick morphology.However, most of them parasitize a large number of hosts. Severalfeatures of cowbirds have been proposed as more general adaptationsto brood parasitism. In this study, we used a recent molecularphylogeny as a historical framework to test the possible adaptationsof the parasitic cowbird, including egg size, eggshell thicknessand energy content of the eggs, length of the incubation period,and growth pattern of cowbird nestlings. We used a recentlydeveloped extension of independent contrasts to test whetherthe five cowbird species deviate from general allometric equations.We generated prediction intervals for a nonparasite that evolvedin the place of the cowbirds. By using these prediction intervals,we found that parasitic cowbirds had not reduced weight or energycontent of their eggs, nor their incubation period over evolutionarytime. Cowbird chicks and those of nonparasitic relatives hadsimilar growth pattern. The only characteristic that separatedparasitic cowbirds from their nonparasitic relatives was anincrease in eggshell thickness. All these findings were robustand resisted the use of three models of character evolution.The fact that most traits exhibited by cowbirds were inheritedfrom a nonparasitic ancestor does not rule out that they areadvantageous for parasitism. Future research should focus onsuch traits of cowbird relatives and on how these traits preadapteda particular lineage to become parasites.     

Parent-Offspring Conflict over Independence in the Herring Gull (Larus argentatus)

Observations on 24 focal nests revealed that, at the time when parental investment in feeding fledging chicks declined, chicks showed a marked increase in begging, particularly in larger broods, whilst parents became less responsive to begging. That chicks suffer a cost from early termination of investment is indicated by the fact that third-hatched chicks, who had attempted (unsuccessfully) to initiate more feeds, were absent from the territory first, rather than the more mature first- and second-hatched chicks. Taken together, these results and related inter- and intra-brood contrasts in behaviour are interpreted as offering support for Trivers ' theory of parent-offspring conflict over the termination of investment.     

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.