The diet of Grey Herons Ardea cinerea breeding at Loch Leven, Scotland, and the importance of their predation on ducklings

Regurgitations from nestling Grey Herons Ardea cinerea at Loch Leven, Scotland, April-July 1981–83, contained mainly three types of prey:perch, brown trout and ducklings. The diet varied markedly through the season but not between years. As the heron breeding season progressed, perch occurred in fewer regurgitations and ducklings in more. There was no seasonal variation in the occurrence of brown trout. Regular collections of duckling down from the heronry suggested that the consumption of ducklings peaked in early June. The ducklings taken by herons were less than 10 days old, Mallard ducklings predominating before mid June and Tufted ducklings later. Most ducklings were taken by only a few herons:those that bred earliest and which initially fed their young on perch. Ducklings became a major part of their diet in the late nestling period and broods fed on ducklings fledged no more or fewer young than others. Herons feeding their young on brown trout took ducklings rarely, if ever. It is argued that variation in the contents of regurgitations resulted from three interacting variables; the type of feeding habitat used by individual Grey Herons, the date at which they bred and the date that regurgitations were produced by their nestlings. The numbers of ducklings taken by herons were calculated to be about 230 in 1981 and 291 in 1982, about 5% of Mallard and 3:b of Tufted ducklings estimated to have hatched annually. Assuming herons continued to consume ducklings at the same rate after their young had dispersed, the figures for Tufted ducklings would be higher but still only about 4% in 1981 and 6% in 1982. Compared with total duckling losses of over 75%, predation by Grey Herons was minor and did not affect duckling production in the years concerned.     

Age-Related Changes in Nestling Diet of the Cooperatively Breeding Green Woodhoopoe

In many socially monogamous bird species, parents of altricial young respond to the increasing demands of growing nestlings by increasing their feeding rate and the size of prey items delivered and by altering the types of prey provided. In some cooperatively breeding species, similar changes in feeding rate and prey size have been documented. However, potential changes in the types of prey delivered, both as nestlings age and by different group members, remain largely unexplored. Moreover, studies rarely compare the diet fed to nestlings with that eaten by the provisioning adults themselves. Here, I show that green woodhoopoe ( Phoeniculus purpureus ) nestlings receive a smaller proportion of spiders and larger proportions of caterpillars and centipedes as they grow older. Both male and female adults delivered a higher proportion of spiders to young nestlings than they ate while self-feeding, probably in response to particular nutritional requirements of the chicks. However, only males altered the proportions of caterpillars and centipedes delivered, providing smaller proportions to young nestlings than eaten themselves. These prey items may be too large for young nestlings to handle, and males may make a greater adjustment in provisioning diet than females because they collect more caterpillars and centipedes than do females. Although there were sex differences in provisioning diet, there were no differences between same-sex breeders and helpers in terms of the overall proportions of prey delivered or the changes with nestling age. Hence, individuals of different reproductive status may be following the same provisioning rules, at least in terms of prey type.     

The diet of breeding Dippers Cinclus cinclus and their nestlings in the catchment of the River Wye, mid-Wales: a preliminary study by faecal analysis

A preliminary study by faecal analysis into the diet of seven pairs of breeding Dippers and their nestlings was undertaken in the catchment of the River Wye in spring 1983. Macro-invertebrate items in faeces could be identified to family and quantified on the basis of mouthparts whilst the macro-invertebrate prey available to each pair of Dippers was assessed quantitatively by riffle-sampling.
In terms of numerical abundance, ephemeropteran nymphs, particularly Baetidae, and trichopteran larvae, particularly Hydropsychidae, were more important to adults and nestlings, respectively. When prey weights were taken into account, trichopteran larvae were the most important macro-invertebrate group to both, but especially to nestlings.
Some macro-invertebrate groups were selected in proportion to their abundance in the environment although indices of electivity indicated that prey selection for adults and nestlings, respectively, was negatively and positively correlated with prey weight. Significant changes in diet were also apparent with nestling age: smaller items, such as ephemeropteran nymphs, were eaten by younger nestlings whilst larger items, such as trichopteran larvae, became more frequent up to Day 15 after hatching.     

Bill harnesses on nestling Tufted Puffins influence adult provisioning behavior

ABSTRACT.   For burrow-nesting seabirds, investigators have examined nestling diet by attaching harnesses to the bills of nestlings to intercept food delivered by the parent. To determine whether this method provides an unbiased estimate of nestling diet, we evaluated its effect on the provisioning behavior of Tufted Puffins ( Fratercula cirrhata ) nesting on Triangle Island, British Columbia. Adults delivering food to nestlings with bill harnesses always hesitated before entering a burrow with food, increasing their susceptibility to kleptoparasitism by gulls, and did not always leave the food intended for the nestling. These responses by adult puffins could lead to underestimates of energy intake rates of nestlings and unreliable comparisons with other species if prey left by adults in nest burrows were the only source of data. We also compared estimates of the species, number, and size of prey delivered by adult puffins as determined by direct observation from blinds to samples of prey collected directly from nest burrows and found that the two sampling techniques produced similar results. However, identifying rare prey species and gathering precise information about prey length, mass, and condition require collection of prey, and we recommend using a combination of techniques to obtain the most reliable estimates of nestling diet.     

Parental Sex Differences in Food Allocation to Junior Brood Members as Mediated by Prey Size

Individual offspring within a brood may receive different amounts of provisioning from the male and female parents. Some hypotheses suggest that this bias is the result of an active and adaptive choice by parents. An alternative hypothesis is that feeding biases arise as a result of a constraint of fitting large prey items into small gapes. In an experiment with pied flycatchers, Ficedula hypoleuca , we tested for sex-biased allocation to junior nestlings in asynchronous broods and whether this could be explained by active parental choice or by passive allocation according to prey size and gape size. In both control broods and broods with experimentally increased degree of asynchrony, prey types did not differ between parents but females brought smaller prey than males at younger but not older nestling stages. At younger but not older nestling stages, the majority of feeds to junior nestlings were from females, and the smaller nestlings consumed smaller prey than older siblings. However, there was no evidence of active preference of small nestlings by females as parents did not differ in the tendency to bypass a begging senior nestling in order to feed a junior nestling. Provisioning rates by females were lower than those by males when nestlings were young and we suggest that foraging time constraints caused by the need to brood offspring result in females bringing smaller prey than males. In turn, the larger prey brought by males was more often transferred to larger offspring after the smaller ones failed to swallow it. In such cases, 'preferential' feeding of small nestlings by females may simply be a passive side effect of foraging constraints and gape-size limitations.     

Diversionary feeding and nestling diet of Hen Harriers Circus cyaneus

Capsule: Diversionary feeding reduced Hen Harrier Circus cyaneus nestlings’ natural food intake by half. Red Grouse Lagopus lagopus scotica chicks constituted 0–4% of all nestling food items. Annually, this reduced annual grouse chick production by 0–6%.

Aim: To quantify proportions of diversionary and natural food (including grouse) delivered to Hen Harrier nestlings in relation to brood size, male status and natural prey abundance.

Methods: We recorded diversionary food provisioned to 25 Hen Harrier broods (2008–15) and studied the diet of 15 broods using observations from hides, nest cameras and regurgitated pellet analysis. Variation in nestling diet was analysed using compositional analysis.

Results: Hen Harriers took 76% of diversionary food provided. Depending on assessment method, average nestling diet was 44–53% diversionary food, 39–55% natural prey (including 24–45% passerines, 4–15% small mammals, 0–4% grouse chicks) and 0–9% unknown items. The amount of diversionary food consumed was not influenced by male status, brood size or natural prey abundance. The number of Red Grouse chicks delivered annually was 34–100% lower than expected under unfed conditions, however, the confidence intervals associated with these estimates were large.

Conclusion: Diversionary food influenced Hen Harrier nestling diet and reduced the number of Red Grouse chicks taken relative to modelled predictions. It may help reduce conflict between Hen Harrier conservation and Red Grouse shooting, but only if overall grouse productivity is thereby maintained or increased.     

Trichomoniasis in a Bonelli's eagle population in Spain

During 1980-97, trichomoniasis was detected in nestlings of Bonelli's eagle Hieraaetus fasciatus in Catalonia (Spain). In 1993 Trichomonas gallinae was isolated in 36% of nestlings (n = 39) and affected 41% of broods (n = 22). Overall, trichomoniasis was one of the most important single nestling mortality factor, accounting for 22% of total chick mortality, and causing the death of 2% of chicks. Trichomoniasis deaths took place during the second half of the nestling period. The median age at death was 45.5 days. Although the presence of the parasite was not related to the composition of the diet or parental age, pairs that developed the disease ate more pigeons and included more often non-adult birds. At present trichomoniasis apparently has little demographic impact on the Bonelli's eagle population in Catalonia, but the eventual spread of this disease in chicks and its unknown effects on adults might be of concern.     

Factors Affecting the Duration of Nestling Period and Fledging Order in Tengmalm’s Owl (Aegolius funereus): Effect of Wing Length and Hatching Sequence

In altricial birds, the nestling period is an important part of the breeding phase because the juveniles may spend quite a long time in the nest, with associated high energy costs for the parents. The length of the nestling period can be variable and its duration may be influenced by both biotic and abiotic factors; however, studies of this have mostly been undertaken on passerine birds. We studied individual duration of nestling period of 98 Tengmalm’s owl chicks (Aegolius funereus) at 27 nests during five breeding seasons using a camera and chip system and radio-telemetry. We found the nestlings stayed in the nest box for 27 – 38 days from hatching (mean ± SD, 32.4 ± 2.2 days). The individual duration of nestling period was negatively related to wing length, but no formally significant effect was found for body weight, sex, prey availability and/or weather conditions. The fledging sequence of individual nestlings was primarily related to hatching order; no relationship with wing length and/or other factors was found in this case. We suggest the length of wing is the most important measure of body condition and individual quality in Tengmalm’s owl young determining the duration of the nestling period. Other differences from passerines (e.g., the lack of effect of weather or prey availability on nestling period) are considered likely to be due to different life-history traits, in particular different food habits and nesting sites and greater risk of nest predation among passerines.     

Temporal changes in prey composition and biomass delivery to African Crowned Eagle nestlings in urban areas of KwaZulu-Natal,South Africa

Globally urban areas are expanding rapidly and this usually has negative effects on biodiversity. Despite this, some species manage to persist in urban areas, as is the case with African Crowned Eagles Stephanoaetus coronatus in KwaZulu-Natal, South Africa. As relatively little is known about African Crowned Eagle nestling diet, especially about how it changes with nestling age, we investigated this with nest camera-traps. We analysed temporal changes in prey composition and biomass delivery during the nestling stage. We also recorded which adults provisioned and attended the nest. The main prey fed to nestlings were Rock Hyrax Procavia capensis and Hadeda Ibis Bostrychia hagedash. Adult males did most of the food provisioning, especially at the start of the nestling period. We found a decrease in total prey number and biomass with nestling age. This may be caused by changing requirements of nestlings. Furthermore, delivering fewer prey at later nestling stages may be a facilitating mechanism to enhance fledging of the nestling. Although the total number of prey brought to the nest decreased, we found an increase in numbers of Vervet Monkey Chlorocebus pygerythrus in the diet with nestling age. This indicated an increase in larger prey being delivered to the nests as the nestling aged. We suggest that this could be caused by increased participation in hunting by the larger female as her nest attendance time decreased as the nestling aged. We conclude with emphasising the importance of protecting the Durban Metropolitan Open Space System (D’MOSS) zones for the persistence of this Near Threatened raptor species, and populations of its prey in urban areas for its breeding success.     

Importance of niche quality for Yellowhammer Emberiza citrinella nestling survival, development and body condition in its native and exotic ranges: the role of diet

The niche hypothesis predicts that some introduced species establish and spread successfully because their new environment provides expanded niche opportunities compared with their native environments. By investigating nestling survival, growth and body condition in relation to diet composition and prey abundance, we tested the prediction that the success of Yellowhammers Emberiza citrinella in New Zealand could be explained by the availability of better quality food resources in its introduced range compared with its native range. We found that Yellowhammer nestlings in New Zealand were larger and heavier than those in Britain, but that nestling survival and body condition did not differ between countries. The preferred prey items, which had some influence on nestling development and survival, were more prevalent in the diet of nestlings in New Zealand, suggesting that nestlings in the introduced range had a superior quality diet. However, there was little evidence to support the prediction that the preferred prey were more abundant in the introduced range, implying that some other factor such as prey accessibility or adult fitness may account for the differences in diet between countries.     

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.     

Effect of Brood Age on Nestling Diet and Prey Composition in a Hedgerow Specialist Bird,the Barred Warbler Sylvia nisoria

The composition and quality of food provided to nestling birds influence their growth and development and offers key insight into the ecological requirements of birds. One bird species whose feeding ecology is poorly understood is the Barred Warbler (Sylvia nisoria), which utilizes semi-natural shrubby vegetation in agroecosystems. Because Barred Warbler nestlings vary greatly in body mass we hypothesised that diet and prey properties (size, diversity, taxonomic composition, and chitin content and resulting body hardness and digestibility) would differ as the nestlings aged. We quantified the diet based on faecal analysis, sampling faecal sacs from the nestlings pooled into three age classes: 2-3 days old, 4-6 d old, and 7-9 d old. Nestlings were provided a wide diversity of food and a strong relationship existed between food characteristics and nestling age. The youngest nestlings (2-3 d old) had the lowest values of each dietary characteristic (diversity, number and total biomass of prey, and individual prey weight), that were significantly lower than the oldest nestlings (7-9 d old). Nestlings aged 4-6 d exhibited intermediate dietary characteristics. Differences in dietary composition of the six major food types showed marked differences between the individual broods and age categories. Percentages of the number and biomass of soft-bodied prey were highest in the diet of 2-3 d and 4-6 d old nestlings, and decreased with increasing age, whereas the opposite trend was observed in the percentage of intermediately and heavily chitinised prey. Parent Barred Warblers probably preferentially select soft-bodied prey for the youngest nestlings, and satisfy the greater energy demands of the older ones by providing them with a greater variety of prey containing more chitin, as well as plant food. The provisioning of less-readily digestible prey to older nestlings suggests that as the quality of food decreases the quantity increases, implying that the youngest nestlings may be physiologically limited as regards their ability to digest more heavily chitinised prey.     

The importance of a main dish: nestling diet and foraging behaviour in Mediterranean blue tits in relation to prey phenology

Insectivorous birds rely on a short period of food abundance to feed their young; they must time their reproduction to match the timing of Lepidoptera larvae, their main prey. Apart from the net result (i.e. birds are timed or mistimed with respect to the food's peak), an important aspect is the possible influence of other factors, such as the seasonality of the environment or the abundance and diversity of species contributing to the caterpillar peak, on birds' phenology and their ability to cope well with unpredictable food supplies. In a 2-year study, we explored the seasonal variation of nestling diet in Mediterranean blue tits Cyanistes caeruleus and how reproductive parameters (nestling condition, provisioning rates) are affected by the phenology and composition of food. We also examined the influence of the synchrony between offspring needs and caterpillar peak in shaping the composition of the nestlings' diet. We found that the effect of synchrony on nestling condition varied between years which may be partially due to differences in food peak attributes. The adequacy of birds' timing in relation to prey phenology affected foraging decisions; those birds that were not able to correctly adjust their timing were forced to rely on less preferred prey (tortricids). In this sense, we found that relative contribution of tortricids (smaller caterpillars but easier to get) and noctuids (preferred prey but more difficult to find) to the diet influenced nestling condition and parental provisioning effort; parents performed fewer feeding events and reared heavier nestlings as the contribution of noctuids to the diet increased. The relationship between the proportion of caterpillars and nestling mass was curvilinear, whereas that parameter was negatively affected by the percentage of pupae. Our results show how changes in diet composition may contribute to explain the effect of mismatching on birds' breeding performance.     

Consequences of the size structure of fish populations for their effects on a generalist avian predator

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.     

Do Tengmalm’s Owls alter parental feeding effort under varying conditions of main prey availability?

We studied the diet composition and behavioural responses to variable food conditions in Tengmalm’s Owls (Aegolius funereus). The abundance of main prey (voles and mice) of owls was higher in the Ore Mountains, Czech Republic, than in the Kauhava region, Finland. We monitored nests continuously by a camera system to estimate the feeding frequency and to identify prey items provided to nestlings. We recorded 990 prey deliveries at six nests in the Ore Mountains and 1,679 prey deliveries at nine nests in the Kauhava region. Mice (Apodemus) and voles (Microtus and Clethrionomys) were the main foods of owls in the Ore Mountains, whereas voles (Clethrionomys and Microtus) and shrews (Sorex) were the main foods in the Kauhava region. In consequence, on average smaller prey items were brought to nestlings at the Finnish site. However, both absolute and relative (per one nestling) feeding frequency was higher in the Kauhava region, and the biomass available to individual nestlings did not differ between the two areas. Moreover, the Finnish and Czech pairs produced about the same number of fledglings. Our results suggest that male owls are able to maintain the amount of food required for chicks by switching to alternative prey, and to increase their prey delivery rates under conditions of reduced abundance of main food.     

The diet of breeding dippers Cinclus cinclus cinclus and their nestlings in southwestern Norway

The diet of dippers in south west Norway was investigated by faecal analysis during the 1985 breeding season. Overall, the diets of adults and nestlings were similar and consisted mostly of nymphs and larvae of Baetidae (mayflies). Leuctridae/Nemouridae (stoneflies). Hydropsychidae, Limnephilidae and Rhyaeophilidae (caddisflies). However, strong trends were apparent with nestling age: large items such as caddisflies declined in adult diet but increased in nestling diet as the chicks grew. The pattern probably reflected the growing energy demands of the brood in a central-place. Because some of the items of dietary importance are scarce in acidic streams, we stress the need for research on the influences of acidification on the ecology of Scandinavian dippers.     

Low survival of parasite chicks may result from their imperfect adaptation to hosts rather than expression of defenses against parasitism

Host parents exhibit a variety of behaviors toward avian brood parasites, but not all of their actions have necessarily evolved in response to costs imposed by parasites. To investigate whether common waxbills (Estrilda astrild) have evolved defenses specifically against parasitic pin-tailed whydahs (Vidua macroura), I studied the specificity and flexibility of host behaviors toward nestlings at two sites that differed significantly in parasitism rates and intensities. I focused on documenting nestling survival because V. macroura young match the elaborate gape morphology of E. astrild nestlings, a pattern that suggests hosts may possess unique defenses against parasite chicks. Parasite young survived significantly worse than host young in mixed broods. However, this apparent discrimination was not associated with parasitism risk as would be expected if defenses had evolved specifically to counter parasitism. Parasite young may have survived poorly compared to host young because individual chicks were less able to stimulate sufficient care from foster parents or because they were more susceptible to nestling competition, disease, or reduced provisioning by hosts. Mortality may have also been exacerbated by poor timing of parasite egg laying. In nonparasitized and parasitized nests, rates of nestling survival were similar, further suggesting that parenting behaviors that result in chick mortality did not evolve solely in response to parasite young. In addition, orange-breasted waxbills (Amandava subflava) and zebra finches (Taeniopygia guttata), rarely parasitized and nonparasitized relatives of E. astrild, experience similar levels of nestling mortality presumably as a result of phylogenetically widespread parenting strategies. Despite the similarity of parasitic V. macroura nestlings and E. astrild nestlings, I found no evidence that E. astrild parents possess defenses that allow for specific discrimination against parasite chicks during the nestling period. Rather than being subject to host defenses evolved in an arms race, Vidua chicks may simply be imperfectly adapted to life in the nests of their hosts.     

ECOLOGY OF THE RED-NECKED FALCON FALCO CHICQUERA IN ZAMBIA

The Red-necked Falcon in southern Zambia is a year-long resident in its breeding territory. The study was conducted on a floodplain and the adjacent acacia savannah in an undisturbed natural environment. The falcon principally nests in natural depressions on frond bases on the leeward side of Borassus Palms but also utilizes old crow and raptor nests. Incubation averaged 33 days and was undertaken by the female. The young fledged after a 36-day nestling period and remained under parental care for up to three weeks after that. Nesting success averaged 1.3 young per nest or 44% of the eggs laid. The post-juvenal moult commenced when the young were five to six months old and continued for six months. Birds comprised 98% of the diet of the falcons. The adults selected larger prey as the nestlings increased in size. The 69-day incubation and nesting period is up to 14 days longer than in similar-sized falcons.     

Foraging ecology of the California gnatcatcher deduced from fecal samples

The California gnatcatcher is a threatened species essentially restricted to coastal sage scrub habitat in southern California. Its distribution and population dynamics have been studied intensely, but little is known about its diet. We identified arthropod fragments in 33 fecal samples of the California gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and nestlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predominated numerically in samples. Spider prey was most diverse, with eight families represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenoptera) were only minor components of the gnatcatcher diet. Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets (Orthoptera) and spiders than adults consumed themselves. Both adults and young consumed more sessile than active prey. Further studies are needed to determine whether arthropods sampled in coastal sage scrub that are common in fecal samples are good indicators of California gnatcatcher habitat. Received: 30 December 1998 / Accepted: 28 April 1999     

Great Spotted Cuckoo Nestlings but not Magpie Nestlings Starve in Experimental Age‐Matched Broods

Nestlings of non‐evicting avian brood‐parasites have to compete for food with foster parents' own nestlings. The outcome of these competitive contests is determined mainly by body size differences between parasitic and host nestlings. As part of the coevolutionary arms race between brood parasites and their hosts at the nestling stage, it has been reported that some host foster parents discriminate against parasitic chicks and are reluctant to feed them. Here, by experimentally creating size‐matched broods of different composition (only magpie Pica pica chicks, only great spotted cuckoo Clamator glandarius chicks or mixed broods), we show that great spotted cuckoo chicks starved in 20.2 per cent (17 of 84) of the parasitized magpie nests even in absence of size asymmetries, while in none (0 of 72) of the nests a magpie chick starved. As far as we know, this is the first record of non‐evictor brood parasitic nestlings starving without being smaller than their host nestmates in a frequently used host species. Nest composition had no effect on chick starvation. The cuckoo nestling starved even in two of the nests occupied by only one cuckoo chick. Our results could be explained by (1) magpies being reluctant to feed cuckoo chicks; (2) parasitic chicks receiving lower‐quality food items or cuckoo nestlings being sensitive to some particular component of the diet (e.g. cereal grains); and (3) the existence of cuckoo chick discrimination ability by magpie foster parents.