Does Foraging Performance Change with Age in Female Little Penguins (Eudyptula minor)?

Age-related changes in breeding performance are likely to be mediated through changes in parental foraging performance. We investigated the relationship of foraging performance with age in female little penguins at Phillip Island, Australia, during the guard phase of the 2005 breeding season. Foraging parameters were recorded with accelerometers for birds grouped into three age-classes: (1) young, (2) middle age and (3) old females. We found the diving behaviour of middle-aged birds differed from young and old birds. The dive duration of middle age females was shorter than that of young and old birds while their dive effort (measure for dive and post-dive duration relation) was lower than that of young ones, suggesting middle-aged birds were in better physical condition than other ones. There was no difference in prey pursuit frequency or duration between age classes, but in the hunting tactic. Females pursued more prey around and after reaching the maximum depth of dives the more experienced they were (old > middle age > young), an energy saving hunting tactic by probably taking advantage of up-thrust momentum. We suggest middle age penguins forage better than young or old ones because good physical condition and foraging experience could act simultaneously.     

Does Seed‐Caching Experience Affect Spatial Memory Performance by Pinyon Jays?

Food‐storing birds use spatial memory to find previously cached food items. Throughout winter, pinyon jays (Gymnorhinus cyanocephalus) rely heavily on cached pinyon pine (Pinus edulis) seeds. Because of a recent severe drought, pinyon pine trees had not produced a significant seed crop for several years. Therefore, 1‐ and 2‐yr‐old birds never had the opportunity to cache and recover seeds and birds 4 or more years of age had not recovered seeds in 3 yr. This study examined whether natural but extreme variability in experience might result in differences in abstract spatial memory ability during a non‐cache recovery test of spatial memory. Three groups of jays were tested for spatial memory ability in an open room analog of the radial arm maze. Two of the groups were 8 mo old: young/minimally experienced birds which had 2 mo of experience in the wild, while young/experienced birds had 5 mo of experience in their natural habitat. The third group, adult, consisted of birds more than 3 yr old, with at least 3 yr of experience in their natural habitat. This was the only group with experience caching pine seeds. All three groups performed equally and well above chance. This suggests that spatial memory is fully developed by 8 mo of age and is not affected by extensive experience in the wild.     

Response to Predation Risk in Urban and Rural House Sparrows

Habitat urbanization may change the density of predators, and it is often assumed that such changes lead to altered predation risk for urban populations of their prey. Although it is difficult to study predation hazard directly, behavior responses of prey species may be informative in inferring such habitat differences. In this study, we compared the risk‐taking behavior of urban and rural house sparrows (Passer domesticus) after simulated attacks by two of their important predators (sparrowhawk Accipiter nisus and domestic cat Felis catus). The birds were startled by moving dummies of these predators and respective control objects, and their risk taking was estimated as their latency to feed after the startle. We found that sparrows responded more strongly (had longer post‐startle feeding latencies) to sparrowhawk attacks than to the control object, and their responses differed between the habitats. First, risk taking of urban birds strongly decreased with age (older birds had longer latencies than young birds), while there was no such age difference in rural birds. Second, young urban birds responded less strongly, while older urban birds responded more strongly to the sparrowhawk than the same age groups of rural birds, respectively. We did not succeed in evoking antipredatory response by simulated cat attacks, because birds responded similarly to the dummy and the control object. Our results support that predation risk, posed at least by avian predators, is different in urban and rural habitats of house sparrows. The increased wariness of older, hence presumably more experienced, urban birds implies that sparrows may be more exposed to predation in cities.     

Evolution of reversed sexual size dimorphism and role partitioning among predatory birds, with a size scaling of flight performance

To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, we combine several previous hypotheses with some new ideas. Owing to their structural and behavioural adaptations for prey capture, predatory birds have better prospects than other birds of defending their offspring against nest predators. This makes sex role partitioning advantageous; one parent guards the offspring while the other forages for the family. Further, among predators hunting alert prey such as vertebrates, two mates because of interference may not procur much more food than would one mate hunting alone. By contrast, two mates feeding on less alert prey may together obtain almost twice as much food as one mate hunting alone. For these reasons, partitioning of breeding labours might be adaptive only in predatory birds. An initial imbalance favours female nest guarding and male foraging: the developing eggs might be damaged if the female attacks prey; their mass might reduce her flight performance; she must visit the nest to lay; and the male feeds her before she lays (‘courtship feeding’). Increased female body size should enhance egg production, incubation, ability to tear apart prey for the young, and, in particular, offspring protection in predatory birds. Efficient foraging during the breeding period then becomes most important for the male. This imposes great demands on aerial agility in males, particularly among predators of agile prey. Flight performance decreases with increasing size in five of six aspects explored. The male must therefore not be too large in relation to the most important prey. For these reasons, he should be smaller than the female. Among predatory birds, size dimorphism increases with the proportion of birds in the diet, which may be explained as follows. Adult birds have mainly one type of predators: other predatory birds. Because almost only these specialists exploit adult birds, they carry out most of the cropping of this prey. A predator of easier prey competes with many other kinds of predators, which considerably reduce prey abundance in its territory. This is not so for predators of adult birds. Further, because birds are extremely agile, the specialized predator can hunt efficiently only within a limited size range of birds, whose flight skill it can match. Increased size dimorphism among these predators therefore should be particularly important for enlarging the combined food base of the pair. A bird specialist may consume much of the available prey in the suitable size range during the breeding period. When the predator's young are large enough to defend themselves, the female aids better by hunting than by guarding the chicks. It is advantageous among bird specialists if she hunts prey of other sizes than does the male, who has by then reduced prey abundance in his prey size class. But among predatory birds hunting easier prey the female gains little by hunting outside the male's prey spectrum, because other kinds of predators will have reduced the prey abundance outside as well as inside the male's preferred size range. Intra-pair food separation through large sexual size dimorphism therefore should be particularly advantageous among predators of birds. This may be the main reason why the degree of size dimorphism increases with the dietary proportion of birds.     

Social learning in birds and its role in shaping a foraging niche

We briefly review the literature on social learning in birds, concluding that strong evidence exists mainly for predator recognition, song, mate choice and foraging. The mechanism of local enhancement may be more important than imitation for birds learning to forage, but the former mechanism may be sufficient for faithful transmission depending on the ecological circumstances. To date, most insights have been gained from birds in captivity. We present a study of social learning of foraging in two passerine birds in the wild, where we cross-fostered eggs between nests of blue tits, Cyanistes caeruleus and great tits, Parus major. Early learning causes a shift in the foraging sites used by the tits in the direction of the foster species. The shift in foraging niches was consistent across seasons, as showed by an analysis of prey items, and the effect lasted for life. The fact that young birds learn from their foster parents, and use this experience later when subsequently feeding their own offspring, suggests that foraging behaviour can be culturally transmitted over generations in the wild. It may therefore have both ecological and evolutionary consequences, some of which are discussed.     

Does prey capture induce area-restricted search? A fine-scale study using GPS in a marine predator, the wandering albatross

In a patchy environment, predators are expected to increase turning rate and start an area-restricted search (ARS) when prey have been encountered, but few empirical data exist for large predators. By using GPS loggers with devices measuring prey capture, we studied how a marine predator adjusts foraging movements at various scales in relation to prey capture. Wandering albatrosses use two tactics, sit and wait and foraging in flight, the former tactic being three times less efficient than the latter. During flight foraging, birds caught large isolated prey and used ARS at scales varying from 5 to 90 km, with large-scale ARS being used only by young animals. Birds did not show strong responses to prey capture at a large scale, few ARS events occurred after prey capture, and birds did not have high rates of prey capture in ARS. Only at small scales did birds increase sinuosity after prey captures for a limited time period, and this occurred only after they had caught a large prey item within an ARS zone. When this species searches over a large scale, the most effective search rule was to follow a nearly straight path. ARS may be used to restrict search to a particular environment where prey capture is more predictable and profitable.     

Foraging Trade‐offs between Prey Size,Delivery Rate and Prey Type: How Does Niche Breadth and Early Learning of the Foraging Niche Affect Food Delivery?

Optimal foraging theory suggests that avian parents should prefer the most energetically efficient (largest) prey items when delivering food to offspring at a central place. However, during periods of high demand, selectivity of prey may decline, leading to the delivery of smaller and/or less nutritious items. We compared foraging trade‐offs between great tits (Parus major) which had a wider feeding niche than blue tits (Cyanistes caeruleus). We also compared the foraging efficiency of cross‐fostered young, which had learned the spatial foraging niche and prey size of the foreign species, to that of control conspecifics. Mean delivery rates did not differ between control and cross‐fostered parents of either species but as delivery rates increased, prey size declined for both species and both treatment groups. However, across the range of increasing delivery rates, parents were able to increase the total biomass of prey delivered. Cross‐fostering did not alter the proportion of different prey taxa in the diet, but cross‐fostered birds shifted the size of the prey taken to that of their foster species. Consistent with their broader feeding niche, great tits, but not blue tits, incorporated more unpalatable items (flies) as delivery rates increased. Although great tits foraged less efficiently in the blue tit niche, paradoxically, blue tits seem to deliver more prey biomass when foraging in the great tit niche.     

Chromaticity in the UV/blue range facilitates the search for achromatically background-matching prey in birds

A large variety of predatory species rely on their visual abilities to locate their prey. However, the search for prey may be hampered by prey camouflage. The most prominent example of concealing coloration is background-matching prey coloration characterized by a strong visual resemblance of prey to the background. Even though this principle of camouflage was recognized to efficiently work in predator avoidance a long time ago, the underlying mechanisms are not very well known. In this study, we assessed whether blue tits (Cyanistes caeruleus) use chromatic cues in the search for prey. We used two prey types that were achromatically identical but differed in chromatic properties in the UV/blue range and presented them on two achromatically identical backgrounds. The backgrounds had either the same chromatic properties as the prey items (matching combination) or differed in their chromatic properties (mismatching combination). Our results show that birds use chromatic cues in the search for mismatching prey, whereupon chromatic contrast leads to a ‘pop-out’ of the prey item from the background. When prey was presented on a matching background, search times were significantly higher. Interestingly, search for more chromatic prey on the matching background was easier than search for less chromatic prey on the matching background. Our results indicate that birds use both achromatic and chromatic cues when searching for prey, and that the combination of both cues might be helpful in the search task.     

Understanding avian nest predation: why ornithologists should study snakes

Despite the overriding importance of nest predation for most birds, our understanding of the relationship between birds and their nest predators has been developed largely without reliable information on the identity of the predators. Miniature video cameras placed at nests are changing that situation and in six of eight recent studies of New World passerine birds, snakes were the most important nest predators. Several areas of research stand to gain important insights from understanding more about the snakes that prey on birds' nests. Birds nesting in fragmented habitats often experience increased nest predation. Snakes could be attracted to habitat edges because they are thermally superior habitats, coincidentally increasing predation, or snakes could be attracted directly by greater prey abundance in edges. Birds might reduce predation risk from snakes by nesting in locations inaccessible to snakes or in locations that are thermally inhospitable to snakes, although potentially at some cost to themselves or their young. Nesting birds should also modify their behavior to reduce exposure to visually orienting snakes. Ornithologists incorporating snakes into their ecological or conservation research need to be aware of practical considerations, including sampling difficulties and logistical challenges associated with quantifying snake habitat use.     

Prey size and ingestion rate in raptors: importance for sex roles and reversed sexual size dimorphism

Compared to other birds, most raptors take large prey for their size, and feeding bouts are extended. However, ingestion rate has largely been overlooked as a constraint in raptors' foraging and breeding ecology. We measured ingestion rate by offering avian and mammalian prey to eighteen wild raptors temporarily kept in captivity, representing seven species and three orders. Ingestion rate was higher for small than for large prey, higher for mammalian than for avian prey, higher for large than for small raptors, and higher for wide-gaped than for narrow-gaped raptors. Mammalian prey were ingested faster by raptors belonging to species with mainly mammals in their diet than by raptors with mainly birds in their diet, but the drop in ingestion rate with increasing prey size was more rapid for the former than for the latter. We argue that the separate sex roles found in raptors, i.e. the male hunting and the female feeding the young, is a solution of the conflict between the prolonged feeding bouts at the nest, and the benefit of rapid resumption of hunting in general, and rapid return to the previous capture site in particular (the prey size hypothesis). Thus, the sex roles differ more when prey takes longer to feed, i.e. from insects to mammals to birds. We then argue that the reversed sexual size dimorphism in raptors, i.e. smaller males than females, results from a conflict between the benefit of being small during breeding to capture the smallest items with the highest ingestion rate among these agile prey types (mammals and bird), and the benefit of being large outside the breeding season to ensure survival by being able to include large items in the diet when small items are scarce (the ingestion rate hypothesis). This hypothesis explains the observed variation in reversed sexual size dimorphism among raptors in relation to size and type of prey, i.e. increasing RSD from insects to mammals to birds as prey.     

Assessment of territory quality and its effects on breeding success in a migrant passerine, the Wheatear Oenanthe oenanthe

This paper examines how a returning migrant assesses the quality of an area as a breeding territory before the period of peak food demand and how effective the assessment is in terms of breeding success. Male Wheatears Oenanthe oenanthe return from Africa to choose territories in the Breckland of eastern England about March, females arriving shortly after males. The food supply was predictable: prey densities during the breeding period (egg-laying to chick independence) were strongly correlated with prey densities at the same sites during the period of arrival and territory establishment. Prey densities were also related to vegetation structure, averaging highest on short turf. Male arrival date and territory size were not significantly related to prey density but were strongly related to vegetation structure, implying that birds used vegetation as an indirect clue to prey availability. Neither territory size nor nest spacing appeared to affect nest losses caused by predators. The major variations in number of young fledged (other than predation) were caused by the number of nestlings hatched and presence of a second brood. Both early arrival and an early first brood improved first-brood success and were necessary for a second brood. Not all birds which arrived early bred early enough for a second brood. First-brood hatching date was strongly negatively correlated with pre-breeding prey availability but not significantly related to vegetation structure. Thus by using vegetation as a clue to habitat quality, some pairs suffered reduced breeding success. This result implies that birds may not be able adequately to assess prey density directly at the time of territory establishment. The critical period for food availability may not be the period of peak demand (nestling period), when food is relatively abundant, but is probably the pre-breeding period when females must accumulate reserves for eggs and when the food supply is poor. Food supply during this period may determine the timing of breeding and the ability to rear a second brood, and may thus have a greater effect on breeding success.     

Habitat use and densities of co‐existing migrant Willow Warblers Phylloscopus trochilus and resident eremomelas Eremomela spp. in Zimbabwe

Capsule Migrant Willow Warblers occupy more woodland types and occur at higher densities than ecologically‐similar resident Afrotropical warblers.

Aims To compare population densities of Willow Warblers and eremomelas in adjacent acacia, mopane and miombo woodlands, and assess the abundance of potential invertebrate prey in each habitat type, in order to investigate whether Palearctic migrants use more open habitats and are more flexible in habitat use than their Afrotropical counterparts in the same feeding guild.

Methods Using distance sampling we carried out four replicated sets of point counts in acacia woodland and three sets of counts in miombo and mopane between December 1999 and February 2000. We noted the tree species in which we saw warblers foraging and took beating‐tray samples of potential arthropod prey present on tree foliage in each of the three habitats.

Results Willow Warbler density in acacia woodland increased from 1.80 ± 0.54 (se) birds/ha in early December to 7.15 ± 1.41 birds/ha in late January after influxes of later arrivals. Densities of Willow Warblers in miombo and mopane were much lower (1.14 ± 0.28 and 0.38 ± 0.23 birds/ha, respectively) and did not show significant changes. Burnt‐necked Eremomelas averaged 0.74 ± 0.34 birds/ha in acacia woodland, and in miombo densities of Green‐capped and Yellow‐bellied Eremomelas were 0.23 ± 0.17 and 0.34 ± 0.26 birds/ha, respectively. Densities in mopane were too low to estimate reliably. Willow Warblers and Green‐capped Eremomelas showed some apparent preferences in tree species used for foraging but differences in tree use were not obviously related to the abundance of arthropod taxa present as potential prey.

Conclusion Willow Warblers occupied more habitats at greater density than similar Afrotropical warblers. They appear to favour acacia, but their settlement patterns and the reasons for disparities between densities of immigrants and residents are unclear.     

Space‐use strategies of wintering Ovenbirds in Belize: causes and consequences

For long‐distance migrants, territoriality and prey biomass during the non‐breeding season have been linked to body condition that can carry over to affect spring migration and breeding events. For Ovenbirds (Seiurus aurocapilla), studies in Jamaica showed that body condition in mid‐season depended on leaf litter prey biomass and declined seasonally as conditions became drier, and that individuals with sedentary (territorial) and wandering space‐use strategies did not differ in age or body condition. During October and November 2010–2011, we radio‐tracked Ovenbirds in Belize to determine if space‐use patterns differed with age and sex, if space‐use strategy influenced foraging behavior or body condition, and if areas used by wanderers and territory owners differed in food abundance or habitat characteristics. Most Ovenbirds (41 of 51, 80.4%) possessed small (1‐ha) territories with largely non‐overlapping cores, but 22.5% (10 of 51) of birds were wanderers (～7‐ha home range). Early season space use was predicted by age class, with most wanderers (90%, 9 of 10) being first‐year birds and most territory owners (63%) being older birds. Sex ratios of wanderers and territory owners did not differ. We found that wanderers may have been at a disadvantage because they had significantly lower foraging rates and lower relative body masses than territorial birds, although baseline corticosterone levels did not differ. Habitat characteristics of areas used by wanderers and territory owners did not differ nor did biomass of ground‐surface arthropods, likely because ranges of most wanderers overlapped those of territory owners. Using stable hydrogen isotopes in feathers, we found that first‐year Ovenbirds that were wanderers tended to have a more northern natal origins than sedentary birds, though the difference was not significant. Longer migration distances could delay arrival and reduce competitive ability. Our results suggest that wandering may not be an alternative and equally successful strategy, at least early in the season, and instead young birds may be competitively excluded from territory ownership.     

Experienced chicks show biased avoidance of stronger signals: an experiment with natural colour variation in live aposematic prey

An important factor for understanding the evolution of warning coloration in unprofitable prey is the synergistic effect produced by predator generalisation behaviour. Warning coloration can arise and become stabilised in a population of solitary prey if more conspicuous prey benefit from a predator's previous interaction with less conspicuous prey. This study investigates whether domestic chicks (Gallus gallus domesticus) show a biased generalisation among live aposematic prey by using larvae of three species of seed bugs (Heteroptera: Lygaeidae) that are of similar shape but vary in the amount of red in the coloration. After positive experience of edible brownish prey, chicks in two reciprocal experiments received negative experience of either a slightly red or a more red distasteful larva. Attacking birds were then divided into two treatment groups, – one presented with the same prey again, and one presented with either a less red or a more red larva. Birds with only experience of edible prey showed no difference in attack probability of the two aposematic prey types. Birds with experience of the less red prey biased their avoidance so that prey with a more red coloration was avoided to a higher degree, whereas birds with experience of the more red prey avoided prey with the same, but not less red coloration. Thus, we conclude that bird predators may indeed show a biased generalisation behaviour that could select for and stabilise an aposematic strategy in solitary prey. This revised version was published online in July 2006 with corrections to the Cover Date.     

Age and hunting success in the brown pelican: influences of skill and patch choice on foraging efficiency

Summary Age-related differences in the foraging efficiency of piscivorous birds may be the results of differences in foraging skill, patch usage, or both. Brown pelicans were observed while foraging around a small Caribbean island. Areas where the birds fed were subdivided into small, homogeneous subunits (patches), and the bird's foraging success and patch use were noted and analyzed using multivariate techniques. Adult birds were found to be better at capturing prey under all conditions than were juveniles, but the differences were small in some patches. The density of prey and the birds' foraging success influenced the foraging efforts of adult and juvenile pelicans to similar degrees. Both age groups utilized local enhancement in their foraging, but such behavior augmented the foraging success only of juvenile birds. Both age groups often fed in patches where their foraging success was quite low. Such behaviour was much more costly for juvenile than for adult pelicans.     

Larval feeding experience influences adult predator acceptance of chemically defended prey

Generalist predatory paper wasps, Polistes dominulus, experience plant secondary defensive compounds as developing larvae through their herbivorous lepidopteran caterpillar prey and as adults through attacking caterpillars while foraging. We evaluated the role that larval and early adult experience with unpalatable prey plays in subsequent foraging choices by adult wasps. For periods of two or four weeks, caged wasps were raised exclusively on caterpillars of either unpalatable Buckeye, Junonia coenia, that sequester substantial levels of iridoid glycosides (IG) or on Painted Lady, Vanessa cardui, that contain very low levels of IG. Wasps were then allowed to forage on both caterpillar species simultaneously. Patterns of prey capture differed significantly based on previous prey experience. Regardless of previous feeding experience, adult wasps overwhelmingly preferred to take Vanessa. Yet Junonia-experienced wasps continued to attack and take back to the nest over 50% more Junonia than did Vanessa-experienced wasps. The longer the wasps' larval experience with Junonia, the more likely they were to capture Junonia caterpillars. However, the life stage at which the wasps experienced Junonia was also influential as young adult experience with the unpalatable prey was more of a deterrent than was experience strictly as larvae for Junonia-experienced wasps. The results demonstrate that, in these predators, previous experience with deterrent chemicals during their larval development alters patterns of prey acceptability to the adult insects.     

Age-dependent diet change,parental care and reproductive costin tawny owls Strix aluco

Tawny owls Strix aluco breeding in nest-boxes were studied in a mixed oak/hornbeam/beech forest located in the Duna-Ipoly National Park 30 km north-west of Budapest, Hungary, during the period 1992–1999. Diet composition, prey mass, breeding performance and body mass of the parents of known age were recorded. Older males had a greater ability to choose alternate prey, delivered a greater mass of prey with a higher feeding frequency and achieved higher productivity than younger males when the availability of the preferred prey declined. The reproductive cost was paid only by young parents. We suggest that the lowest breeding performance, which was observed with young parents in adverse weather conditions, may be due to both the lower ability of these younger birds to exploit alternative prey and to their poor body condition which resulted in them providing fewer resources to their offspring because of their need to provide for their own survival.     

Do Blue Tits time their breeding based on cues obtained by consuming buds?

ABSTRACT.   Many temperate-zone birds must track seasonal variation in food availability to time breeding and enhance reproductive success. However, the external cues birds use to fine-tune sexual development and timing of reproduction remain unclear. One possibility is that birds may use chemical substances in plants and bud tissues as a reliable predictor of leaf flush and the appearance of caterpillars, the preferred prey of many insectivorous birds during the breeding season. However, few data on seasonal shifts in key plant material consumption are available. To test this hypothesis, we examined the gizzard contents of Corsican Blue Tits ( Cyanistes caeruleus ), a small passerine bird with a breeding schedule tightly linked to the phenology of oak trees. We quantified and compared the consumption of tree buds by birds captured during winter (nonbreeding) and early spring (prebreeding) and found that bud use by Blue Tits was limited and constant through time. Fewer than 30% of birds had buds in their gizzards during the critical prebreeding period, and these items represented less than 1% of gizzard contents. It is unlikely that this limited use of buds allowed birds to track a potential chemical signal at the time of reproductive decision making. Unless more data on the consumption of plant material become available, we suggest that other environmental factors be examined to help identify the cues used by temperate-zone birds to time their reproduction.     

How Do Predators Learn to Recognize a Mimetic Complex: Experiments with Naive Great Tits and Aposematic Heteroptera

We tested the importance of innate wariness, avoidance learning, memory and generalization for the formation of predatory behaviour in naive great tits (Parus major) towards mimetic complex of four aposematic species of true bugs (Insecta: Hemiptera: Heteroptera): Lygaeus equestris, Spilostethus saxatilis, Pyrrhocoris apterus and Graphosoma lineatum. The birds showed almost no innate wariness against the aposematically coloured bugs, although a hidden wariness elicited by defensive chemicals of some of the bug species is not excluded. Naive birds learned to avoid different species at different rates, which resulted in different prey mortalities. The avoidance learning was faster when the defensive chemicals produced an immediate irritating effect (particularly when squirted into distance – G. lineatum) than when they caused sickness several minutes after the consumption (P. apterus). The experience of birds from learning to avoid a particular species of bug affected their subsequent behaviour to other species – experience with better‐defended species resulted in longer attack latencies, more cautious attacks, broader generalization and lower prey mortality. The least defended species, P. apterus, benefited from the experience of birds with better‐defended species, whereas the birds' experience with P. apterus did not reduce mortality risk of the other species comparably. Judging from the inexperienced young birds, the mimetic relationships are likely to be quasi‐Batesian. However, as wild‐caught great tits avoid all the four species to the same extent, the relationships may become more mutualistic (quasi‐Müllerian) in later phases of learning under natural conditions. The relationships among species in the mimetic complex thus seem to depend on the amount of experience of the bird predators.