Pollution-related changes in diets of two insectivorous passerines

Insectivorous birds living in polluted areas are not only exposed to pollutants but they may also be affected by changes in their invertebrate food. The populations of many invertebrate species are affected by environmental pollution and such changes may lead to differences in the diet of insectivorous birds. We examined nestling food quality (invertebrate composition and heavy metal levels) and breeding performance of two cavity-nesting passerines, the Great tit, Parus major, and the pied flycatcher, Ficedula hypoleuca, in an area with long-term heavy metal pollution by a copper smelter. There were no differences in feeding frequencies or the amount of food that parents provided to their nestlings between polluted and unpolluted sites, but food quality in a polluted area differed from that of the control area in both bird species. P. major took more beetles and variable “flying insects” and less caterpillars (of smaller size) and moths in the polluted area as compared to the unpolluted one. F. hypoleuca ate more beetles and larvae and less moths and spiders in the polluted area. Breeding success of P. major was better when the nestling diet contained a large proportion of caterpillars and the relationship was especially strong in the polluted area. On the contrary, F. hypoleuca broods succeeded equally well with variable diets. Our data suggest that a more opportunistic forager, F. hypoleuca, is less vulnerable to a changing invertebrate composition caused by human environmental impacts than a caterpillar specialist, P. major. In a heavy metal polluted area, F. hypoleuca seems to be more sensitive to a decreased amount of Ca rich food items (e.g. snails) while P. major suffers especially from the lack of carotenoid rich caterpillars. Our results emphasize the importance of secondary environmental changes, like food quality, in addition to direct impacts of pollutants.     

The biosystematics and evolution of the Polyalthia hypoleuca species complex (Annonaceae) of Malesia. III. Floral ontogeny and breeding systems

Aspects of floral ontogeny, breeding systems, and hybridization potential for selected members of the monophyletic Polyalthia hypoleuca complex (Annonaceae) of Malesia were investigated. Complete intrafloral dichogamy (protogyny) was found in all five members examined. Further, these five tree species had flowers developing in several serial “cohorts,” the flowers of any one cohort maturing in synchrony resulting in complete intracohort dichogamy. Two modes of the timing of maturation of successive floral cohorts within an individual were observed. In the first (P. hypoleuca and P. sumatrana), the onset of stigma receptivity of successive cohorts was separated by 2 days, resulting in complete intercohort dichogamy within any given individual. This mode of ontogeny probably acts to reduce geitonogamy and stamen-carpel interference within an individual. Two distinct “sets” of trees existed in these populations. The trees of one set were functionally carpellate at times when the trees of the other set were functionally staminate. Functional status for the two sets was reversed the next day. This pattern of complete intraset dichogamy with temporally shifted sets probably leads to enhanced pollen transfer by beetles between, but not within, the sets. The second mode of successive cohort maturation involved serial cohorts that achieved stigma receptivity day after day such that staminate and carpellate phase flowers were simultaneously present in a given individual. The second mode permits geitonogamy and intraindividual, interfloral stamen-carpel interference. P. discolor, P. glauca, and P. multinervis exhibited both modes to varying degrees. In addition, autogamy was not detected for P. glauca, P. hypoleuca, and P. sumatrana. Results from manual pollination experiments are consistent with the hypothesis that P. glauca and P. hypoleuca are self-incompatible, and a bidirectional hybrid cross between these two species yielded no fruit set.     

Growth and mortality of nestling great tits (Parus major) and pied flycatchers (Ficedula hypoleuca) in a heavy metal pollution gradient

We studied nestling growth, growth abnormalities, mortality and breeding success of two hole-nesting passerines, the great tit (Parus major) and the pied fly-catcher (Ficedula hypoleuca), at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland in 1991–1993. The main pollutants in the area are heavy metals and sulphuric oxides. Exposure of birds to heavy metals was shown by measuring their faecal concentrations. Copper, nickel and lead contents of nestling faeces were high near the factory and decreased with distance away from the pollution source. F. hypoleuca nestlings suffered high mortality very close to the factory complex, but did relatively well at all other sites. Breeding success of P. major was below background levels up to 3–4 km from the pollution source and nestlings grew poorly close to the factory. Growth abnormalities of legs and wings in F. hypoleuca nestlings were significantly more common near the factory than farther away. In contrast, F. hypoleuca nestlings grew equally well at all distances. The poor breeding success of F. hypoleuca close to the factory complex is probably related to the high amount of heavy metals in its diet, and low availability of calcium-rich food items may enhance this effect. We suggest that the poor breeding success of P. major is related to habitat changes that have taken place around the factory. The different responses of these two bird species are probably due to their different diet. Our results show convincingly that species-specific differences in response should be carefully considered when planning schemes for air pollution monitoring.     

Modifications to a molt‐based ageing system proposed by Wolfe et al. (2010)

ABSTRACT Wolfe et al. (2010 . Journal of Field Ornithology 81: 186–194) proposed a coding system for ageing birds based on the sequence of molts and plumages, which is more practical than a calendar‐based system, especially in tropical and southern latitudes where species often breed across 1 January. The Wolfe–Ryder–Pyle (hereafter, W–R–P) three‐letter system is based on recognition of molt cycle (first, second, third, definitive, and so on) and plumage phase (juvenile, supplemental, formative, alternate, and basic). For example, a bird in First Cycle Formative plumage is coded as FCF. We propose the use of two additional code options that further refine age brackets. First, we suggest the use of an “after” or “A” code in place of the “C,” or cycle code, where an earlier molt cycle or plumage can be ruled out. For example, a bird that exhibits Staffelmauser might be aged as after‐third cycle basic, or TAB. Second, we suggest using “pre” or “P” in place of the “C,” or cycle code, when birds are actively molting, such as for birds undergoing the second prebasic molt or SPB. For both codes, we discuss their applicability using examples based on actual banding data. Our proposed codes will improve the utility of the W–R–P system by better refining age brackets and by expanding its applicability to a diverse array of taxa.     

Corallite wall and septal microstructure in scleractinian reef corals: Comparison of molecular clades within the family Faviidae

Recent molecular phylogenies conflict with traditional scleractinian classification at ranks ranging from suborder to genus, challenging morphologists to discover new characters that better agree with molecular data. Such characters are essential for including fossils in analyses and tracing evolutionary patterns through geologic time. We examine the skeletal morphology of 36 species belonging to the traditional families Faviidae, Merulinidae, Pectiniidae, and Trachyphylliidae (3 Atlantic, 14 Indo‐Pacific, 2 cosmopolitan genera) at the macromorphological, micromorphological, and microstructural levels. Molecular analyses indicate that the families are not monophyletic groups, but consist of six family‐level clades, four of which are examined [clade XV = Diploastrea heliopora; clade XVI = Montastraea cavernosa; clade XVII (“Pacific faviids”) = Pacific faviids (part) + merulinids (part) + pectiniids (part) + M. annularis complex; clade XXI (“Atlantic faviids”) = Atlantic faviids (part) + Atlantic mussids]. Comparisons among molecular clades indicate that micromorphological and microstructural characters (singly and in combination) are clade diagnostic, but with two exceptions, macromorphologic characters are not. The septal teeth of “Atlantic faviids” are paddle‐shaped (strong secondary calcification axes) or blocky, whereas the septal teeth of “Pacific faviids” are spine‐shaped or multidirectional. Corallite walls in “Atlantic faviids” are usually septothecal, with occasional trabeculothecal elements; whereas corallite walls in “Pacific faviids” are usually trabeculothecal or parathecal or they contain abortive septa. Exceptions include subclades of “Pacific faviids” consisting of a) Caulastraea and Oulophyllia (strong secondary axes) and b) Cyphastrea (septothecal walls). Diploastrea has a diagnostic synapticulothecal wall and thick triangular teeth; Montastraea cavernosa is also distinct, possessing both “Pacific faviid” (abortive septa) and “Atlantic faviid” (paddle‐shaped teeth) attributes. The development of secondary axes is similar in traditional Atlantic faviids and mussids, supporting molecular results placing them in the same clade. Subclades of “Pacific faviids” reveal differences in wall structure and the arrangement and distinctiveness of centers of rapid accretion. J. Morphol. 272:66–88, 2011. © 2010 Wiley‐Liss, Inc.     

DISPERSION, POPULATION ECOLOGY AND MIGRATION OF EASTERN GREAT REED WARBLERS ACROCEPHALUS ORIENTALIS WINTERING IN MALAYSIA

A population of 400–600 Acrocephalus orientalis wintering in a Phragmites habitat at 3°N in West Malaysia was studied during four northern hemisphere winters, by means of systematic mist-netting. Data from other study-areas, other habitats and other winters are also used. Intensive mist-netting appears to have made birds move over longer distances than they did in the absence of disturbance, and to have led to the emigration of marked birds from the study-area. Trapping also affected feeding behaviour, resulting in weight-loss; repeated trapping may have increased mortality. Males and females could be separated by means of wing-length in fresh plumage. Females were largely confined to Phragmites; males were more numerous on the edge of reed-beds and in scrub vegetation. Males suffered greater feather-wear than females. As measured by the trapping rate, birds were uniformly distributed throughout the Phragmites habitat, at the same density in different winters. Undisturbed birds used a “home-range” of 1–4 ha, overlapping with 15–50 other individuals. Disturbed birds overlapped with 100–200 others. Individual birds returned to exactly the same “home-range” in successive winters. After correcting for the effects of disturbance and incomplete sampling, the proportion of adults ringed in one winter which returned in the next is estimated as 65% in each of two study-areas. This is a minimum estimate of the annual survival rate for adults. Mean total body-weights were at a minimum in midwinter (November-February). Fat-free weights were also lower in midwinter than in autumn and spring. Body-moult was observed in March and April. Moult of the flight-feathers takes place between July and September, on the breeding grounds or slightly to the south. Females departed on spring migration between 10 and 25 May; males some 11–14 days earlier. Adults arrived in autumn between 8 September and 7 October; males and females often came in in separate “waves”. Females were absent for only about 127 days, about the minimum required for migration, breeding and moult. Dates of migration match those of the more northern breeding populations. Spring departure is later than dates of passage recorded in south China; hence birds of this population appear to make long nights. On average, birds departing in spring carried about 9 g of fat, roughly 40% of total fat-free body-weight. This is about half the energy reserve required for the entire journey. Dates of passage in central China are consistent with a hypothesis that they make the journey (4,500-5,000 km) in two “hops”. A few birds which remained light until very late in the spring showed a significantly lower return rate in the next year. Most birds arriving in autumn appear to have carried 1–2 g of fat, but some were at or below the normal fat-free weight. Many birds appear to have lost weight soon after arrival. Returning ringed adults were amongst the very first birds trapped in September. Individual birds appear to have migrated on very similar dates in different years: many of the dates of trapping differed by 2 days or less in successive years. Trapping rates reached a peak in early October and then declined rapidly, reaching the midwinter level by 21 October. The decline coincided with the differential disappearance of juvenile birds. However, birds collected at this time had adequate fat reserves, and the disappearance appears to have preceded the period of food-shortage. It is suggested that the loss of juvenile birds resulted from behavioural interactions favouring the more dominant individuals, as has been described for several temperate zone residents. The first few weeks in the wintering area may thus be the critical period of mortality during the year. Because birds from different breeding areas are expected to be mixed in the winter-quarters, and vice versa, local mortality factors in winter may affect a number of breeding populations. High adult survival rates have been recorded in several other birds which breed in the temperate zones and winter in the tropics. In general their breeding success appears to be high, so the first-year mortality must be high. The closely related A. arundinaceus, which winters in Africa, differs from A. orientalis in size, wing-shape, timing of spring migration and timing of moult. These differences can be interpreted as adaptations to different environmental (primarily climatic) factors experienced during migration and on the breeding grounds. The segregation of males and females into different habitats probably reduces inter-sexual competition in winter, but this is not necessarily its primary function. Males collected in the evening in Phragmites had smaller fat reserves than females, suggesting that the females are better adapted to this habitat. The large size of the males is probably maintained in part by sexual selection in the breeding season. On the other hand, the size of females and their habitat is probably limited by the specialisation of their nest. These factors would suffice to explain the sexual dimorphism in size and habitat.     

7. THE ANGOLA KINGFISHER

Cantrell, M. A. &; Evans, S. M. 1981. Auditory communication in the blue waxbills Uraeginthus. Ostrich 52:104-107.

Field observations on the function of calls in the Redcheeked Cordon Bleu Uraeginthus bengalus, the Bluecapped Cordon Bleu U. cyanocephalus, and the Purple Grenadier U. (=Granatina) ianthinogaster were made in Kenya, East Africa. Individuals of all three species were usually seen in male-female pairs, and distinct calls were used to synchronize movement. Flight calls were made in rapid succession on take-off, but less frequently during flight. When birds on or near the ground became separated, repeated contact calls were used to locate and rejoin the partner. Alarm calls were rarely heard in the field, but usually originated from perched birds in relatively safe positions.

Laboratory experiments on the reactions of solitary caged birds to playback of calls were conducted using male U. bengalus. Separate playbacks of contact and flight calls both elicited a series of contact calls from the “lost” individual. In addition, a strong tendency to move towards contact calls was observed, the experiment confirming field observations that this call is used to locate and rejoin a partner after separation. Feeding birds usually flew up to perches in response to alarm calls and their own vocalizations were considerably reduced. The paper examines the function of these calls in pair synchronization and predator avoidance.     

CHARACTERISTICS OF TERRITORIAL AND MATING CALLS IN WILLOW PTARMIGAN LAGOPUS L. LAGOPUS

ABSTRACT

During territorial behaviour and pair formation willow ptarmigan cocks and hens use several different calls. Cocks use mainly a “flight call”, a “ground call” and three different “threat calls”. Hens give similar calls to cocks. It is suggested that the structure of the calls is well adapted to (1) transmit their possible information content over long distances, and (2) make localization easier for birds during the territorial display periods, which take place mainly in poor light at dusk and dawn. We also suggest that the cock and hen calls express different degrees of aggressiveness, and that hen calls, in addition to attracting cocks, function as territorial “keep out” signals to other hens.     

REPTILIAN PHYSIOLOGY AND THE FLIGHT CAPACITY OF ARCHAEOPTERYX

Current scenarios frequently interpret the Late Jurassic bird Archaeopteryx as having had an avian-type physiology and as having been capable of flapping flight, but only from “the trees downward.” It putatively lacked capacity for takeoff and powered flight from the ground upward. Data from extant reptiles indicate that if Archaeopteryx were physiologically reptilian, it would have been capable of ground upward takeoff from a standstill, as well as “trees downward” powered flight. This conclusion is based largely on a previously unrecognized attribute of locomotory (skeletal) muscle in a variety of extant reptiles: During “burst-level” activity, major locomotory muscles of a number of active terrestrial taxa generate at least twice the power (watts kg^?1 muscle tissue) as those of birds and mammals. Reptilian physiological status also helps resolve the apparently uneven development of various flight support structures in Archaeopteryx (e.g., well-developed flight features but relatively unspecialized pectoral girdle, supracoracoideus muscles, etc.). Endothermy and capacity for longer-distance powered flight probably evolved only in Early Cretaceous birds, which were the first birds to have a keeled sternum, strap-like coracoid, and hypocleidium-bearing furcula.     

L’origine et l’évolution des oiseaux : 35 années de progrès

The origin and evolution of birds: 35 years of progress. Birds are dinosaurs – specifically, small feathered and flighted theropod dinosaurs that probably originated in Laurasia during the Late Jurassic over 140 million years ago. They are most closely related to other small theropods such as dromaeosaurs and troodontids, terrestrial predators that were fleet-footed hunters. The origin of birds is a classic example of two kinds of macroevolution: the phylogenetic origin of the group, and the sequential assembly of adaptations such as flight that are indelibly associated with birds. These adaptations were not assembled all at once. Rather, a great many characteristics associated with birds and flight first appeared in non-avian dinosaurs, where they were used for many purposes other than flight. These included insulation, brooding, and probably display and species recognition. Birds diversified steadily but gradually after their origin, which is identified with the origin of flight (Archaeopteryx); forelimb and other flight-associated features evolved more rapidly than features associated with the posterior skeleton. The first birds grew more slowly than extant birds do, and more like other small Mesozoic dinosaurs; like them, they probably matured sexually well before they completed their active skeletal growth. The origin of flight is not a problem of “trees down” or “ground up,” but rather an examination of the order in which diagnostic flight characters evolved, and what each stage can reveal about the functions and habits of bird outgroups at those evolutionary junctures.     

COMPARISONS AND FUNCTIONS OF SKY-DANCING DISPLAYS OF CIRCUS HARRIERS: UNTANGLING THE MARSH HARRIER COMPLEX

Simmons, R. 1991. Comarisons and functions of sky-dancing displays of Circus harriers: untangling the marsh harrier complex. Ostrich 62:45-51.

African Marsh Hamers Circus ranivorus perform aerial displays known as “sk-dancing” most frequently just before breeding and at other times during territorial takeovers. Both mares and females display and food supplements to seven pairs over two years verified sexual selection arguments that birds in better condition display more freuently than unfed controls. Typical sky-dancing birds soared to 400 m or more, and performed up to 20 U-shaped undulations in a horizontal plane, while sky-spiruffing birds performed vertical displas, dropping in a series of descending U-shaped undulations, whilst twisting about their axis. Displaying girds stimulated others to perform and up to eight birds displayed in the same aerial arena. I interpret both displas as mainly territorial in function but rovide evidence that they also have a mate attraction component. in form, the display resembles that or the Australasian Hamer C. uproxi mans, but not that of the European Marsh (C. aeruginosus) nor the Reunion Malagasy (C. a. maifardii Hamer, providing evidence contrary to the traditional belief that African birds are subspecies of aeruginosus     

Migratory Orientation of Blackcaps (Sylvia atricapilla): Population-specific Shifts of Direction during the Autumn

The population-specific orientation of two groups of blackcaps (Sylvia atricapilla), one from southwest Germany, the other from easternmost Austria, was studied outdoors in Emlen funnels. We investigated whether a seasonal shift in the migratory direction — as expected for the Austrian birds from ringing recoveries — occurs under experimental conditions and in a seasonally constant magnetic field. The West German birds, for which no shift was expected, oriented southwest during the entire season. The Austrian birds oriented southeast in October and southsouthwest in November. The clockwise shift by about 60° occurred within a 10-day period. The results indicate that in this species seasonal changes of migratory direction are probably based on an endogenous program, occur without the birds actually migrating and are independent of changes in the magnetic field. Our results provide further evidence that directional shifts in Sylvia warblers may be controlled by a different mechanism than in pied flycatchers (Ficedula hypoleuca).     

High divorce rates in Corsican blue tits: how to choose a better option in a harsh environment

We investigate which hypothesis, the “better mate hypothesis” or the “better territory hypothesis” best explains the unusually high divorce rate (59%) in a population of blue tits (Parus caeruleus) living in a sclerophyllous habitat characterised by severe environmental constraints (trophic, parasitic, climatic) on the island of Corsica, France. Using data from the breeding seasons 1985–1998 and from a brood size experiment (1990–1993) we examined the causes of divorce and their consequences on breeding performance, mate assortment and territory choice. Breeding performance had no significant effect on whether birds re‐united or divorced in the next breeding season. Re‐uniting pairs did better than divorced females and the latter improved their breeding performance compared to prior to divorce, but this was mainly due to age and territory effects. There were no differences in male performance depending on whether they re‐united or divorced. The age combination of pairs did not differ between re‐uniting and divorcing pairs, but mate assortment changed after divorce with males re‐mating more often with older partners than females. Manipulation of brood size showed a trend for birds with enlarged broods to divorce more. Pairs responded significantly to territory quality by divorcing more often in poor than in good breeding sites. Both faithful pairs and male divorcees had shorter breeding dispersal distances than female divorcees. Divorce rates were determined by the large differences in quality among breeding sites. Males, whatever their status, usually retained their previous territory whereas divorced females moved significantly longer distances and improved their breeding site. Moving to a better territory after divorce benefits only females which appear to be the choosing sex in the decision to divorce. This study strongly supports the “habitat mediated hypothesis” and we suggest that the large observed intraspecific variation in the magnitude of divorce rates in many species of birds is mostly determined by habitat characteristics.     

Are nest sites actively chosen? Testing a common assumption for three non-resource limited birds

Many widely-accepted ecological concepts are simplified assumptions about complex situations that remain largely untested. One example is the assumption that nest-building species choose nest sites actively when they are not resource limited. This assumption has seen little direct empirical testing: most studies on nest-site selection simply assume that sites are chosen actively (and seek explanations for such behaviour) without considering that sites may be selected randomly. We used 15 years of data from a nestbox scheme in the UK to test the assumption of active nest-site choice in three cavity-nesting bird species that differ in breeding and migratory strategy: blue tit (Cyanistes caeruleus), great tit (Parus major) and pied flycatcher (Ficedula hypoleuca). Nest-site selection was non-random (implying active nest-site choice) for blue and great tits, but not for pied flycatchers. We also considered the relative importance of year-specific and site-specific factors in determining occupation of nest sites. Site-specific factors were more important than year-specific factors for the tit species, while the reverse was true for pied flycatchers. Our results show that nest-site selection, in birds at least, is not always the result of active choice, such that choice should not be assumed automatically in studies of nesting behaviour. We use this example to highlight the need to test key ecological assumptions empirically, and the importance of doing so across taxa rather than for single “model” species.     

The Magnetic Field as a Reference System for Genetically Encoded Migratory Direction in Pied Flycatchers (Ficedula hypoleuca Pallas)

To see whether the migratory orientation of pied flycatchers (Ficedula hypoleuca Pallas) is genetically encoded with respect to the earth magnetic field a group of young birds was hand-raised. They were thus prevented from ever experiencing the sky. The birds were tested in autumn 1980 and 1981 in the local geomagnetic field (Fig. 1) and in three artificial fields (Fig. 2a-c). The results show that their magnetic compass matures independent of any experience with the sky and contains sufficient information for the birds to orient toward their migratory direction.     

CELL SIZE DIFFERENTIATION IN THE BLOOM-FORMING DINOFLAGELLATE GYMNODINIUM CF. NAGASAKIENSE1

Two subpopulations differing essentially by their mean cell size were observed regularly in cultures and natural samples of the naked dinoflagellate Gymnodinium cf. nagasakiense Takayama et Adachi (currently known as Gyrodinium aureolum Hulburt), a species which frequently forms red tides in North European seas. “Large” cells represented the typical forms; they were morphologically similar to cells of the closely related Japanese species G. nagasakiense, which did not form any subpopulation of reduced size. “Small” and “large” cells of G. cf. nagasakiense had the same DNA content, but the nucleus of the former appeared to be much more condensed during interphase. Each cell type was able to divide and had its own growth dynamics; therefore, any intermediary between pure populations of “small” and of “large” cells were observed in culture. The “large” form generated a “small” cell by an atypical budding-like division, whereas the “small” form gave back a “large” form, once it ceased to divide, by simple enlargement of its cell body. Factory inducing cell size differentiation are yet unclear. Neither nitrogen nor phosphorus starvation induced a significant increase in the relative proportion of “small” and budding cells. Although cell size differentiation is associated with the formation of gametes in a variety of dinoflagellates, we demonstrated that “small” cells of G. cf. nagasakiense are able to divide asexually, in contrast to gametes of most other species. The high proliferative power of “small” cells as compared with normal cells suggests that they could play a significant role during red tides of G. cf. nagasakiense; in contrast, cells of the Japanese species G. Nagasakiense could sustain high growth rates with larger cell size because this species generally blooms in waters much warmer than those found in northern Europe.     

Social Structure and the Development of Helping Behaviour in the Bell Miner (Manorina melanophrys,Meliphagidae)

The hypothesis that bell miners (Manorina melanophrys) improve their alloparenting skills during the period spent as helpers was tested by means of comparing: a) the frequency of nestling care activities, b) the frequency of nestling attendance “mistakes”, c) the gizzard contents and items brought to nestlings, and d) interactions at the nest with the breeders, for helpers of different ages. Results show that young birds made fewer feeding visits to the nestlings and made more empty (i.e. non-feeding) visits than older helpers. The few “mistakes” detected were also made by young helpers. The proportion of food items brought to the nestlings consisting of arthropods was smaller for very young helpers (≤ 3.8 months) than for older helpers. Sexually mature helpers also had relatively more arthropods than psyllid sugary covers (a food item very easy to locate and capture) in their gizzards than immatures in winter, but this difference was marginally not significant. Young helpers must learn their place within the group hierarchy, but no clear division of labor in the alloparental activities studied was detected, which might have increased the effect of learning during the period birds spent as helpers.     

Localization of Passerine Seeet and Mobbing Calls by Goshawks and Pygmy Owls

Goshawks and pygmy owls responded to recordings of passerine alarm calls by correctly orienting to their source. The seeet, or “aerial predator” alarm call which is generally assumed to be “non-localizable”, while it elicited fewer responses than did mobbing calls, was nevertheless accurately localized by all birds that did respond. The evolution of alarm calls is discussed in terms of efficient prey communication, following Darwin's “antithesis principle”, rather than predator selection for non-localizability.