Dual parasitism of Fork-tailed Drongos by African and Jacobin Cuckoos

The interaction between brood parasitic cuckoos and their hosts represents a traditional example of coevolution, whereby obligate interspecific brood parasitic cuckoos completely rely on their hosts to do their parental care for them by laying their eggs in the host’s nest. This thesis brings together a great deal of information documenting and clarifying the interactions between different species of hosts and their respective parasitic cuckoos in Bangladesh. I recorded parasitism rates to determine the extent of brood parasitism and to identify the host species that were parasitised by sympatric cuckoos. Four parasitic cuckoos were documented: the Asian koel ( Eudynamys scolopacea), the common hawk cuckoo (Cuculus varius; previously known as Hierococcyx varius), the pied cuckoo (Clamator jacobinus) and the Indian cuckoo (Cuculus micropterus). These cuckoos were sympatric and parasitised different host species, including the house crow (Corvus splendens), the long-tailed shrike (Lanius schach), the common myna (Acridotheres tristis), the jungle babbler (Turdoides striatus) and the black drongo (Dicrurus macrocercus). All of these cuckoo species are obligate brood parasites. The Asian koel utilised the following three hosts: the house crow, the common myna and the long-tailed shrike. The latter was recorded for the first time as a host for the Asian koel in Bangladesh. We found that koel eggs were highly non-mimetic to those of common myna and long-tailed shrike, but showed good mimicry to house crow eggs. Indian cuckoos showed excellent egg mimicry with the eggs of their black drongo hosts, as did common hawk cuckoos and pied cuckoos with their jungle babbler host. The hosts accepted the eggs of all four cuckoo species. However, the common myna was more likely to abandon nests parasitised by the koel than unparasitised ones. All of the host species suffered the costs of koel parasitism, showing reduced breeding success. Proximity to fruit trees was an important predictor of the probability of parasitism in the three koel host species studied. There was a significant positive relationship between nest volume and probability of parasitism by Asian koels. Furthermore, the colonial breeding house crows suffered comparatively less parasitism than the other two koel host species. Long-tailed shrike nests close to conspecific neighbours were less likely to be parasitised, and the risk of parasitism was increased in nests lower to the ground. The risk of parasitism increased during the breeding season for house crows and common mynas. All three Asian koel hosts tolerated multiple parasitism. We investigated whether there was any interspecific competition among the sympatric cuckoos. In theory, sympatric parasites should show niche segregation through variation in host use. As predicted, each cuckoo species parasitised different host species; however, host use overlapped in common hawk cuckoos and pied cuckoos, but interspecific competition was reduced because these two cuckoo species have different breeding seasons. Furthermore, there was a significant difference in parasitism rate among the three main habitats: human habitations, mixed scrub forests and monoculture plantations. This indicated that different cuckoos favour specific habitats, even if their favourite host also occurs elsewhere. Finally, I tested responses against foreign eggs by the cuckoo hosts as well as by potential cuckoo hosts in the study area. For this purpose, I used differently sized and coloured model eggs. Common mynas and jungle babblers accepted all non-mimetic eggs, as did most of the house crows (91 %). Long-tailed shrikes rejected 75 % of the non-mimetic model eggs. Finally, black drongos turned out to be strong rejectors and could do so without damaging any of their own eggs, most likely because they grasped and ejected the non-mimetic model egg. This result indicates that the black drongo has been in a coevolutionary arms race with the Indian cuckoo since drongos accepted mimetic cuckoo eggs. Species such as the Oriental magpie robin (Copsychus saularis), red-vented bulbul (Pycnonotus cafer) and Asian pied starling (Gracupica contra), which likely have no history of interaction with cuckoos, accepted 100 % of the non-mimetic model eggs. In conclusion, our findings describe host nest use cues used by the Asian koel, which may provide background for further studies in other sympatric brood parasites. In spite of the high degree of acceptance of parasitic eggs, the breeding success of both cuckoos and hosts should be more closely studied to obtain a better understanding of the costs of parasitism. Future experimental studies are highly recommended to achieve a better understanding of host responses to Asian cuckoo species.

ABSTRACTGlobal declines in cuckoo numbers have been variously attributed to reduced prey availability; changes in their hosts’ ranges; or climate-induced changes. We used data from two Southern African Bird Atlas Projects to determine whether migrant cuckoo species breeding in South Africa, Lesotho and Swaziland have experienced range shifts during the past 25 years; and whether such changes corresponded to shifts in host species distribution. Changes in presence/absence data indicated that of the nine cuckoo species found breeding in this region, six showed reductions in range (African Cuckoo, African Emerald Cuckoo, Diederik Cuckoo, Great Spotted Cuckoo, Jacobin Cuckoo and Red-chested Cuckoo); two are expanding (Black Cuckoo and Levaillant’s Cuckoo) and one remains stable (Klaas’s Cuckoo). Occupancy modelling of these data indicated that the host ranges of only four of the nine species (Great Spotted Cuckoo, Klaas’s Cuckoo, Levaillant’s Cuckoo and Red-chested Cuckoo) predicted cuckoo distribution in the first instance. Of these, only in Levaillant’s Cuckoo is range expansion related to changes in the range of its sole known host species in the region, the Arrow-marked Babbler. These results imply that factors other than changes in the ranges of their hosts appear to be driving the range reductions observed in six southern African cuckoo species.

On Wicken Fen and nearby watercourses eastern England, parasitism by cuckoos, Cuculus canorus, declined from 26 and 16 of reed warbler (Acrocephalus scirpaceus) nests in 1985 and 1986, respectively...

In coevolutionary arms races, like between cuckoos and their hosts, it is easy to understand why the host is under selection favouring anti-parasitism behaviour, such as egg rejection, which can lead to parasites evolving remarkable adaptations to 'trick' their host, such as mimetic eggs. But what about cases where the cuckoo egg is not mimetic and where the host does not act against it? Classically, such apparently non-adaptive behaviour is put down to evolutionary lag: given enough time, egg mimicry and parasite avoidance strategies will evolve. An alternative is that absence of egg mimicry and of anti-parasite behaviour is stable. Such stability is at first sight highly paradoxical. I show, using both field and experimental data to parametrize a simulation model, that the absence of defence behaviour by Cape bulbuls (Pycnonotus capensis) against parasitic eggs of the Jacobin cuckoo (Clamator jacobinus) is optimal behaviour. The cuckoo has evolved massive eggs (double the size of bulbul eggs) with thick shells, making it very hard or impossible for the host to eject the cuckoo egg. The host could still avoid brood parasitism by nest desertion. However, higher predation and parasitism risks later in the season makes desertion more costly than accepting the cuckoo egg, a strategy aided by the fact that many cuckoo eggs are incorrectly timed, so do not hatch in time and hence do not reduce host fitness to zero. Selection will therefore prevent the continuation of any coevolutionary arms race. Non-mimetic eggs and absence of defence strategies against cuckoo eggs will be the stable, if at first sight paradoxical, result.

The southern African subspecies of Jacobin CuckooClamator jacobinus serratusis a brood parasite of a range of host species. While Jacobin Cuckoos do not evict host young, previous research has found that host young rarely survive the nestling period. Here we provide the first records of Jacobin Cuckoo parasitism of a new host species, the Southern Pied BabblerTurdoides bicolor. We investigate rates of brood parasitism and the survival of host young. The Southern Pied Babbler is one of the largest recorded hosts for Jacobin Cuckoos and, unusually, we find that host young tend to survive the nestling period and maintain similar body mass to host young in unparasitized broods. However, host young were less likely to survive to independence than young raised in unparasitized nests, suggesting a post‐fledging reproductive cost to hosts.

Most mimicry systems involve imperfect mimicry, whereas perfect and high-fidelity mimicry are rare. When the fidelity of mimicry is high, mimics might be expected to have the upper hand against their antagonists. However, in coevolving systems, diversification of model phenotypes may provide an evolutionary escape, because mimics cannot simultaneously match all model individuals in the population. Here we investigate high-fidelity mimicry in a highly specialized, Afrotropical brood parasite–host system: the African cuckoo and fork-tailed drongo. Specifically, we test whether host egg polymorphisms are an effective defence against such mimicry. We show, using a combination of image analysis, field experiments and simulations, that: (1) egg colour and pattern mimicry of fork-tailed drongo eggs by African cuckoos is near-perfect on average; (2) drongos show fine-tuned rejection of foreign eggs, exploiting unpredictable pattern differences between parasitic eggs and their own; and (3) the high degree of interclutch variation (polymorphic egg ‘signatures’) exhibited by drongos gives them the upper hand in the arms race, with 93.7% of cuckoo eggs predicted to be rejected, despite cuckoos mimicking the full range of drongo egg phenotypes. These results demonstrate that model diversification is a highly effective defence against mimics, even when mimicry is highly accurate.

An understanding of avian brood parasitism requires investigation of a complicated system of co-evolutionary adaptations and interactions between host and parasite. Selection favors parasites which can best utilize their hosts while at same time favoring hosts which best avoid parasitism. Brownheaded Cowbird (Molothrus ater) hosts have several behavioral adaptations for decreasing parasite success. Both nest desertion and nest reconstruction in which a cowbird egg and usually a host egg are buried involve loss of host's eggs and energy required to build a new nest (Friedmann 1963). Ejection of a cowbird egg by a host, which requires accurate discrimination between parasite and host eggs, is probably an energetically preferable defense (Rothstein 1970). Yet all of these anti-parasite defenses operate after parasite egg is laid and consequently do not prevent loss of host eggs removed by parasite. Rothstein (1970:133) pointed out that the advantageous form of host adaptation is to avoid being One way to avoid parasitism is to guard nest site with aggressive behavior. Host aggression towards brood parasites has been recognized clearly in European Cuckoo (Cuculus canorus) (Rothschild and Clay 1952) and several African cuckoos (Friedmann 1948). Hosts frequently mob cuckoos and may attack when nest is approached too closely. Edwards et al. (1949) and Smith and Hosking (1955) conducted field experiments on English songbirds using models of European Cuckoos. In general they found that models were attacked violently by regular host species but not by birds seldom parasitized. Antagonistic behavior towards Brownheaded Cowbird has not been investigated previously, and only a few reports of host aggression appear in literature. Friedmann (1963:33) stated that On whole, majority of American species of passerine birds do not act as if they recognize an enemy in However, in an earlier work (Friedmann 1929:195) he stated most birds are so vigilant of their nests that often a laying cowbird must be subject to considerable attack, or a least be witness of many intimidation displays on part of victim. Seland r and LaRue (1961) reviewed li era ure on host aggression to cowbirds. Aggressive host-parasite interactions have been reported for Song Sparrow (Melospiza melodia) by Nice (1943). She observed a few instances when Song Sparrows actually att cked a female cowbird. The American Red-

On 30 August the Council met throughout most of the day; the Fellows met ]ate in the afternoon, and the Fellows and Elective Members met in the evening. The Council held a second meeting the morning of 2 September, as did the Fellows. 1965 meeting. The Eighty-third Stated Meeting will be held from 23 to 27 August 1965 at Columbus, Ohio, by invitation from the Ohio State University, the Ohio State Museum, The Ohio Historical Society, the Wheaton Bird Club, and the Columbus Audubon Society. 1966 meeting. The Eighty-fourth Stated Meeting will be held during early September, 1966, at Duluth, Minnesota, by invitation of the University of Minnesota, Duluth. 1967 meeting. The Eighty-fifth Stated Meeting has tentatively been set to be held at Toronto, Ontario, by invitation of the Royal Ontario Museum of Zoology and Paleontology. Awards. The Brewster Memorial Award, by action of the Council, was made to Herbert Friedmann, of the Los Angeles County Museum, Los Angeles, California, for his work entitled Host relationships o] the parasitic cowbirds as well as his work on other birds displaying brood parasitism. The citation reads: Dr. Friedmann began his lifelong study of brood parasitism in birds in the 1920's with those unpopular but fascinating New World inhabitants, the cowbirds. His interest in this strange biological phenomenon has since led him further afield, and he has produced important monographs on other parasitic birds, including the honey-guides, African cuckoos, and parasitic weaverbirds. His interest in the cowbirds has not diminished, however, as evidenced by the publication in 1963 of his Host Relationships of the Parasitic Cowbirds, a definitive summary of the information available to date. Friedmann's contributions to our knowledge of brood parasitism are outstanding even when viewed in the context of his impressive total list of publications, which reflect the exceptionally broad scope of his ornithological interests. In recognizing his accomplishments

Brood parasitism is a breeding strategy adopted by many species of cuckoos across the world. This breeding strategy influences the evolution of life histories of brood parasite species.In this study, we tested whether the degree on diet specialization is related to the breeding strategy in cuckoo species, by comparing brood parasite and nonparasite species. We measured the gradient of diet specialization of cuckoos, by calculating the Gini coefficient, an index of inequality, on the multiple traits describing the diet of species. The Gini coefficient is a measure of statistical dispersion on a scale between 0 and 1, reflecting a gradient from low to high specialization, respectively. First, we tested the strength of the phylogenetic signal of diet specialization index among cuckoo species worldwide. Then, we ran phylogenetic generalized least square (PGLS) models to compare diet specialization, distribution range, and body mass of parasitic and nonparasitic cuckoo species, considering the phylogenetic signal of data.After adjusting for the phylogenetic signal of the data and considering both, species distribution range and species body mass, brood parasitic cuckoos were characterized by higher diet specialization than nonbrood parasitic species. Brood parasitic species were also characterized by a larger breeding distribution range than nonparasitic species.The findings of this study provide an additional understanding of the cuckoos’ ecology, relating diet and breeding strategies, information that could be important in conservation ecology.

Despite major differences between human and avian colour vision, previous studies of cuckoo egg mimicry have used human colour vision (or standards based thereon) to assess colour matching. Using ultraviolet-visible reflectance spectrophotometry (300-700 nm), we measured museum collections of eggs of the red-chested cuckoo and its hosts. The first three principal components explained more than 99% of the variance in spectra, and measures of cuckoo host egg similarity derived from these transformations were compared with measures of cuckoo host egg similarity estimated by human observers unaware of the hypotheses we were testing. Monte Carlo methods were used to simulate laying of cuckoo eggs at random in nests. Results showed that host and cuckoo eggs were very highly matched for an ultraviolet versus greenness component, which was not detected by humans. Furthermore, whereas cuckoo and host were dissimilar in achromatic brightness, humans did not detect this difference. Our study thus reveals aspects of cuckoo-host egg colour matching which have hitherto not been described. These results suggest subtleties and complexities in the evolution of host-cuckoo egg mimicry that were not previously suspected. Our results also have the potential to explain the longstanding paradox that some host species accept cuckoo eggs that are non-mimetic to the human eye.

Parasites face a trade-off if the highest quality hosts are also most resistant to exploitation. For brood parasites, well-defended host nests may be both harder to parasitize and harder to predate, leading to better survival of parasitic chicks. This trade-off could be accentuated if brood-parasitic adaptations to reduce front-line defences of hosts, such as mimicry of hawks by Cuculus cuckoos, do not deter hosts which aggressively mob raptors. Here we investigate the costs and benefits to the African cuckoo (Cuculus gularis) of specializing on a highly aggressive host species, the fork-tailed drongo (Dicrurus adsimilis). Field experiments showed that drongos strongly attacked and mobbed both cuckoo and hawk models, implying that hawk mimicry does not deter front-line defences against African cuckoos. Attacks on cuckoo and hawk models generally declined after the egg stage but attacks on snake models sharply increased, suggesting drongos may treat hawks more like cuckoos than predators. We suggest that the cost to cuckoos of parasitizing an aggressive host may be alleviated by subsequent benefits to their offspring, since drongo nests survived better than nests of other species with similar nesting ecology. These results are indicative of a trade-off between host quality and susceptibility for a brood parasite.

Of cuckoos and other cheats

Strategic Variation in Mobbing as a Front Line of Defense against Brood Parasitism

Nestling cuckoos, Cuculus canorus , eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus , as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula , or song thrush, T. philomelos , chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick9s rapid begging call (‘si, si, si, si ...’), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.

In the arms race between avian brood parasites and their hosts, several adaptations and counter‐adaptations have evolved. The most prominent host defence is rejection of parasitic eggs. We experimentally parasitized nests of 10 potential host species breeding in sympatry with four different cuckoo species in an area in Bangladesh using differently coloured model eggs to test host responses. In four species we introduced both mimetic and non‐mimetic eggs. Black DrongosDicrurus macrocercus, hosts of the Indian CuckooCuculus micropterus, rejected all model eggs. Common MynasAcridotheres tristisand Jungle BabblersTurdoides striataaccepted all eggs regardless of mimicry. These two species are parasitized by Asian KoelsEudynamys scolopaceus, Common Hawk‐cuckooHierococcyx variusand, in the case of Jungle Babblers, Jacobin CuckoosClamator jacobinus. Pied MynasGracupica contra, with no records of parasitism in our study area, also accepted all eggs regardless of mimicry. In the six remaining species, all of which lay spotted eggs, we introduced only non‐mimetic eggs. Black‐hooded OriolesOriolus xanthornusrejected all model eggs, even though we have found no records of natural parasitism. Long‐tailed ShrikesLanius schachand House CrowsCorvus splendens, hosts of Asian Koels, rejected 75 and 9.1% of model eggs, respectively. Large‐billed CrowsCorvus macrorhynchos, apparently not used as hosts in our study area, accepted all blue but rejected all brown model eggs. Oriental Magpie‐RobinsCopsychus saularisand Red‐vented BulbulsPycnonotus caferaccepted all non‐mimetic model eggs. In Black Drongos, Long‐tailed Shrikes and Black‐hooded Orioles, all model eggs were ejected within 24 h of introduction. The results show considerable variation in egg rejection rates among various species, providing baseline data for further investigation of co‐evolutionary interactions between brood parasites and hosts in this region.