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.

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.

Roads may have negative or positive effects on wildlife. I surveyed birds along a c. 21 km transect alongside a road from Katima Mulilo to Ngoma bridge in the Zambezi Region, north-eastern Namibia, and on a second transect (control) parallel to the first one and 200–400 m away from the road. The habitat is Kalahari Woodland, partly transformed to cultivated fields. The number of bird species was similar on both transects (56 vs. 48 species; x2 = 0.62, p > 0.05), but the number of breeding pairs (overall population density) was much higher away from the road than close to it (409 vs. 283 pairs; x2 = 22.9, p < 0.01). The Shannon’s Diversity Index was very similar, while Pielou’s Evenness Index was identical in both transects compared. Five species (Blue Waxbill, Burchell’s Starling, Cape Turtle Dove, Fork-tailed Drongo and Grey-headed Sparrow) were dominant on both transects, while the African Grey Hornbill was dominant only on the transect away from the road, whereas the Red-billed Hornbill and Grey Go-away-bird were dominant only close to the road. Four species (African Grey Hornbill, Cape Turtle Dove, Meyer’s Parrot and White-browed Scrub Robin) had population densities significantly higher on the transect away from the road than close to it. However, population densities of nine other species did not differ significantly between the two transects. In general, the avian communities along and away from the road were similar, probably because traffic volume was rather low and the land cover on both transects was similar in terms of natural vegetation and degree of transformation.

In April 2013, a transect c. 1100 km long with 100 points arranged in 5 sections was designed in northern Namibia between Ruacana Watefall (W) and Kongola (E) to study avian diversity in relation to gradual changes in precipitation (c. 350 mm in W to c.600 mm in E). In total, 81 bird species were recorded in all 100 points, but in particular section, the numbers were low, ranging from 22 to 38 species. In overall, the most frequent and most numerous (dominant) were the following species: Cape Turtle Dove, Blue Waxbill, Grey-headed Sparrow, Laughing Dove and Fork-tailed Drongo. Together they comprised 42.2 % of all individuals recorded. All of them, except for the Fork-tailed Drongo, were granivores. Only nine species were recorded in ten or more points. Besides the above-mentioned dominant species, the following other were in this group: Black-chested Prinia, Black-throated Canary, Pied Crow and White-browed Scrub Robin. In particular section the number of dominant species ranged from 5 to 7, without a gradient. Two species, the Cape Turtle Dove and Blue Waxbill, remained dominant in all fi ve sections. Th e Laughing Dove and Fork-tailed Drongo — in four sections, and the Grey-headed Sparrow — in three sections. Although, no gradient in species diversity, evenness, and dominance structure was recorded, signifi cant diff erences between two most western and two most eastern sections were apparent. Two species were more frequent and numerous in the eastern than in the western sections: White-browed Scrub Robin and Cape Turtle Dove; while the following species were more frequent and numerous in the western than the eastern sections: African Palm Swift , Black-chested Prinia, Black-throated Canary, Blue Waxbill, Grey-headed Sparrow and Pied Crow.

Field research techniques are constantly evolving to meet the needs of the scientific community. There is a growing need for field biology studies to shift towards increasing efficiency and quality of results while simultaneously decreasing cost in both the researcher’s time and resources. I tested the efficacy of using multiple recorded birdcall lures (n = 172 species) to improve mist-net captures at a subtropical African savanna setting. Capture success was compared between passive and birdcall enhanced mist-nets during winter and summer seasons. Results suggest that the use of birdcalls does significantly increase the total number of birds caught in both seasons and also increases the diversity of passerine species. Conventional passive mist-nets without an audio lure were initially productive but their capture rate subsequently decreased as sampling days progressed. Birdcall lure enhanced mist-nets had a constant capture output during the summer season. The most responsive birds to audio lures were gregarious species (e.g. Pycnonotus barbatus, Dryoscopus cubla, Prionops plumatus, Phoeniculus purpureus, Turdoides jardineii and Lamprotornis chalybaeus) and the aggressive Dicrurus adsimilis and Acridotheres tristis. I conclude that birdcall lures can be used in summer and winter seasons to improve mist-net captures especially for studies focusing on gregarious and aggressive passerine species in a sub-tropical African savanna setting.

Species complexes of widespread African vertebrates that include taxa distributed across different habitats are poorly understood in terms of their phylogenetic relationships, levels of genetic differentiation and diversification dynamics. The Fork‐tailed Drongo (Dicrurus adsimilis) species complex includes seven Afrotropical taxa with parapatric distributions, each inhabiting a particular bioregion. Various taxonomic hypotheses concerning the species limits of the Fork‐tailed Drongo have been suggested, based largely on mantle and upperpart coloration, but our understanding of diversity and diversification patterns remains incomplete. Especially given our lack of knowledge about how well these characters reflect taxonomy in a morphologically conservative group. Using a thorough sampling across Afrotropical bioregions, we suggest that the number of recognized species within the D. adsimilis superspecies complex has likely been underestimated and that mantle and upperpart coloration reflects local adaptation to different habitat structure, rather than phylogenetic relationships. Our results are consistent with recent phylogeographic studies of sub‐Saharan African vertebrates, indicating that widespread and often morphologically uniform species comprise several paraphyletic lineages, often with one or more of the lineages being closely related to phenotypically distinct forms inhabiting a different, yet geographically close, biome.

Abstract The Zambezian Baikiaea woodlands fall entirely within the Kalahari Woodland biome, a subset of savanna. In 2015, the line transect method was employed to study avian assemblages associated with Zambezian Baikiaea. In total, 10 transects were designed along a straight 12 km long line, so that each transect was 1.2 km long. A total of 88 species represented by 1190 pairs were recorded. On average, there were 42.9 species per transect. The overall density was 35.8 pairs/km, ranging from 29.2 to 44.2 on particular transects. Overall, Streptopelia capicola was the only dominant species. It was also the only species recorded as dominant on all the transects. The following other species were recorded as dominant: Cercotrichas leucophrys, Laniarius aethiopicus, Turtur chalcospilos, Dicrurus adsimilis, Lamprotornis nitens, Upupa africana, Apalis flavida, Ploceus velatus, Tchagra australis and Numida meleagris. The proportion of dominant species (cumulative dominance) varied from 18.9 to 37.7 (x = 28.5; n =...

Mixed-species foraging flocks (MSFFs) of birds can be defined as aggregations of more than two species that actively initiate and continue their association while foraging, without being drawn to a single resource. MSFFs have been well documented for terrestrial habitats globally, but rarely in southern Africa. This study describes the composition of MSFFs in two habitat types (Acacia and Combretum) within the southern Kruger National Park, South Africa during the late dry season. Thirty-one MSFFs were recorded in each of the two habitat types, with 1251 individuals of 74 different species being observed. We found that compared to Combretum, (mean: 10.7 ± 5.2 s.d.) Acacia had significantly more individuals per MSFFs (mean: 21.5 ± 12.6 s.d.) and more species per MSFF (Acacia mean: 8.7 ± 3.5 s.d.; Combretum mean: 5.9 ± 1.7 s.d.). The mean number of individuals per species per 31 MSFFs was 9.3 (± 4.5 s.d.) and 7.6 (± 5.6 s.d.) in the Acacia and Combretum habitat types respectively. The most frequently occurring species in both habitat types was the Fork-tailed Drongo (Dicrurus adsimilis). There was a significant association between certain species pairs in both habitats. Future studies in this area could be done to investigate the reasons behind the differences in MSFF sizes and species numbers between habitats. The season during which this study was performed excluded all summer migrants and a similar investigation in the wet season may reveal a different MSFF composition.Conservation implications: Understanding the dynamics and compositions of MSFFs, could form a valuable component of avian biodiversity monitoring both in and outside of protected areas. Within a given area, changes in the composition and behaviour of MSFFs over time could potentially be used as early indicator of threats to biodiversity.Keywords: avian; habitat; savanna

Robert Godfrey's 1941 publication drawing on schoolboys’ essays, in Xhosa, Bird-Lore of the Eastern Cape Province described two species of birds as herding stock by whistling to them. These were the umcelu (wagtail species of the Motacilla genus) and intengu (fork-tailed drongos, Dicrurus adsimilis). It is possible to take this extraordinary claim about herding birds seriously. The birds have reputations throughout eastern and southern Africa for interactions with both people and stock. Vernacular and ecological knowledge provides a context for these claims: the honeyguide (Indicator indicator) and sentry birds – for example, the go-away bird (Corythaixoides leucogaster) – are widely recognized in Africa as effective interspecies communicators. Ecological studies of ‘heterospecific alarm calls’ have confirmed that birds and mammals communicate with each other. Research suggests, however, that if drongos and wagtails do whistle to herds and flocks, they seek advantages other than the safety of stock. Experimental research on this interspecies network would reveal more about participation by and affordances to stock, birds, and insects. But, what the boys say about their engagement with this network can be taken seriously. Social worlds theory, with its emphasis on collaboration without consensus and imperfect translations, supports a discussion of networks of interspecies communication.

Different species of brood parasitic birds, which lay their eggs in the nests of host foster-parents, rarely target the same host species population. We report brood parasitism of Fork-tailed Drongos Dicrurus adsimilis in the southern Kalahari Desert by both African Cuckoo Cuculus gularis and Jacobin Cuckoo Clamator jacobinus serratus. Drongos are the only known host for the African Cuckoo, and were more frequently parasitised by this species (21.8% nests). Nevertheless, parasitism rates suggest that in the Kalahari, drongos are also an important host for Jacobin Cuckoo (4.6% nests). Jacobin Cuckoos likely compete with African Cuckoos for drongo hosts, as exemplified by the occurrence of both African and Jacobin Cuckoo eggs in the same drongo clutch. The drongo's defensive adaptations to parasitism by African Cuckoos, including egg rejection, may also curtail parasitism by Jacobin Cuckoos. The extent of competition between these cuckoo species and whether they possess adaptations to prevent one another's access to drongo hosts remains to be explored.

Interspecific communication is common in nature, particularly between mutualists. However, whether signals evolved for communication with other species, or are in fact conspecific signals eavesdropped upon by partners, is often unclear. Fork-tailed drongos (Dicrurus adsimilis) associate with mixed-species groups and often produce true alarms at predators, whereupon associating species flee to cover, but also false alarms to steal associating species' food (kleptoparasitism). Despite such deception, associating species respond to drongo non-alarm calls by increasing their foraging and decreasing vigilance. Yet, whether these calls represent interspecific sentinel signals remains unknown. We show that drongos produced a specific sentinel call when foraging with a common associate, the sociable weaver (Philetairus socius), but not when alone. Weavers increased their foraging and decreased vigilance when naturally associating with drongos, and in response to sentinel call playback. Further, drongos sentinel-called more often when weavers were moving, and weavers approached sentinel calls, suggesting a recruitment function. Finally, drongos sentinel-called when weavers fled following false alarms, thereby reducing disruption to weaver foraging time. Results therefore provide evidence of an 'all clear' signal that mitigates the cost of inaccurate communication. Our results suggest that drongos enhance exploitation of a foraging mutualist through coevolution of interspecific sentinel signals.

Animals commonly steal food from other species, termed interspecific kleptoparasitism, but why animals engage in kleptoparasitism compared with alternate foraging tactics, and under what circumstances they do so, is not fully understood. Determining what specific benefits animals gain from kleptoparasitism could provide valuable insight into its evolution. Here, we investigate the benefits of kleptoparasitism for a population of individually recognizable and free-living fork-tailed drongos (Dicrurus adsimilis) in the southern Kalahari Desert. Drongos engaged in two foraging behaviours: self-foraging for small insects or following other species which they kleptoparasitized for larger terrestrial prey that they could not capture themselves. Kleptoparasitism consequently enabled drongos to exploit a new foraging niche. Kleptoparasitism benefitted drongos most in the morning and on colder days because at these times pay-offs from kleptoparasitism remained stable, while those from self-foraging declined. However, drongos engaged in kleptoparasitism less than expected given the overall high (but more variable) pay-offs from this behaviour, suggesting that kleptoparasitism is a risky foraging tactic and may incur additional foraging costs compared with self-foraging. This is the first study to comprehensively investigate the benefits of facultatively engaging in kleptoparasitism, demonstrating that animals may switch to kleptoparasitism to exploit a new foraging niche when pay-offs exceed those from alternate foraging behaviours.

Investigating a link between bill morphology, foraging ecology and kleptoparasitic behaviour in the fork-tailed drongo

Kleptoparasitism by attacks versus false alarm calls in fork-tailed drongos

Parasitism generally imposes costs on victims, yet many victims appear to tolerate their parasites. We suggest that in some cases this may be because parasites provide victims with mitigating benefits, paradoxically giving rise to selection for advertisement rather than concealment by parasites. We investigate this possibility using the interaction between an avian kleptoparasite, the fork-tailed drongo (Dicrurus adsimilis), and one of its victims, the pied babbler (Turdoides bicolor). Combining field observations and a playback experiment, we demonstrate that a conspicuous vocal signal broadcast by drongos perched waiting to steal food from foraging babblers allows the latter to improve their own foraging efficiency, although not to the same extent as that experienced in response to conspecific sentinel calling. We argue that "sentinel" calling by drongos may originally have arisen as a means of manipulating babblers: because babblers find more food items and venture into the open more in response to these vocalizations, drongos are presented with more kleptoparasitism opportunities. However, the resulting benefit to babblers could be sufficient to reduce selection for the evolution of defenses against drongos, and the current situation may represent a rare example of an interspecific relationship in transition from a parasitism to a mutualism.

Despite the prevalence of vocal mimicry in animals, few functions for this behaviour have been shown. I propose a novel hypothesis that false mimicked alarm calls could be used deceptively to scare other species and steal their food. Studies have previously suggested that animals use their own species-specific alarm calls to steal food. However none have shown conclusively that these false alarms are deceptive, or that mimicked alarm calls are used in this manner. Here, I show that wild fork-tailed drongos (Dicrurus adsimilis) make both drongo-specific and mimicked false alarm calls when watching target species handling food, in response to which targets flee to cover abandoning their food. The drongo-specific and mimicked calls made in false alarms were structurally indistinguishable from calls made during true alarms at predators by drongos and other species. Furthermore, I demonstrate by playback experiments that two of these species, meerkats (Suricata suricatta) and pied babblers (Turdoides bicolor), are deceived by both drongo-specific and mimicked false alarm calls. These results provide the first conclusive evidence that false alarm calls are deceptive and demonstrate a novel function for vocal mimicry. This work also provides valuable insight into the benefits of deploying variable mimetic signals in deceptive communication.

Summary Most small birds inhabiting temperate latitudes in the Holarctic increase basal metabolic rate (BMR) in winter, a pattern thought to reflect the up‐regulation of metabolic machinery required for enhanced winter cold tolerance. In contrast, patterns of seasonal BMR variation in birds inhabiting subtropical latitudes are largely unknown. In this study, we investigate seasonal BMR changes in species from subtropical latitudes, and analyse global variation in the direction and magnitude of these responses. We estimated winter and summer BMR in five species resident in the Kalahari Desert, using flow‐through respirometry to measure O2 consumption and CO2 production in birds held overnight in a field laboratory. In all five species, mass‐specific BMR was significantly lower in winter than in summer, with mean reductions of 23% in African scops‐owls (Otus senegalensis), 30% in pearl‐spotted owlets (Glaucidium perlatum), 35% in fork‐tailed drongos (Dicrurus adsimilis), 29% in crimson‐breasted shrikes (Laniarius atrococcinneus), and 17% in white‐browed sparrow‐weavers (Plocepasser mahali). An analysis of global variation in seasonal BMR changes reveals that their magnitude and direction vary with latitude, ranging from pronounced winter increases at high latitudes where winters are extremely cold, to the opposite pattern in warmer, subtropical environments. Our empirical results for five species, taken together with the analysis of global variation, are consistent with the hypothesis that winter metabolism in subtropical environments is driven primarily by the need for energy and/or water conservation rather than cold tolerance.

Many animals must trade-off anti-predator vigilance with other behaviours. Some species facilitate predator detection by joining mixed-species foraging parties and 'eavesdropping' on the predator warnings given by other taxa. Such use of heterospecific warnings presumably reduces the likelihood of predation, but it is unclear whether it also provides wider benefits, by allowing individuals to reduce their own vigilance. We examine whether the presence of an avian co-forager, the fork-tailed drongo (Dicrurus adsimilis), affects rates of vigilance (including sentinel behaviour) in wild dwarf mongooses (Helogale parvula). We simulate the presence of drongos-using playbacks of their non-alarm vocalizations-to show that dwarf mongooses significantly reduce their rate of vigilance when foraging with this species. This is, to our knowledge, the first study to demonstrate experimentally that a mammal reduces vigilance in the presence of an avian co-forager.

Investigations were carried out during 2001-2004 to study the impact of biointensive integrated pest management (BIPM), chemical pesticide intensive integrated pest management (CIPM) modules and non-integrated pest management (non-IPM) modules (farmers' practice) on the natural enemies of insect pests of castor in Andhra Pradesh. BIPM module proved to be relatively safer to natural enemies with 16.13 and 66.10 % average field parasitization of Achaea janata (L.) eggs and larvae by Trichogramma chilonis Ishii and Microplitis maculipennis Szepligeti, compared to 6.92 and 21.2, 8.80 and 24.00, 8.92 and 22.35 % in CIPM module and non-IPM modules 1 and 2, respectively. M. maculipennis cocoon number per plant increased with increase in duration after treatment in the BIPM module whereas it decreased in CIPM and non-IPM modules. Similarly, average parasitisation by Charops obtusus Morley (3.54%), Rhogas spp. (4.60%), Apanteles hyposidrae Wilkinson (13.85%), Euplectrus maternus Bhatnagar (7.92%) on A. janata larvae and Cotesia flavipes Cameron (8.96%) on Spodoptera litura (F.) was higher in the BIPM module compared to CIPM module (1.65, 1.59, 3.50, 2.37 and 2.49%) and non-IPM modules 1(1.16, 0.80, 2.70, 1.20 and 2.68%) and 2 (1.50, 1.19, 2.80, 3.82 and 1.99%), respectively. BIPM module had higher population of predators like Chrysoperla sp., Cheilomenes sexmaculata (Fabricius), Cantheconidea furcellata (Wolff), Rhynocoris kumarii Ambrose and Livingstone and spiders per 10 plants (8.45, 3.41, 3.27 and 7.10) than CIPM module (1.75, 2.90, 1.38, 1.45 and 1.40) and non-IPM modules 1(1.20, 1.82, 1.00, 1.00 and 1.80) and 2 (1.97, 2.41, 1.32, 1.22 and 2.90), respectively. Black drongo ( Dicrurus adsimilis Blyth) and Indian myna ( Acridotheres tristis (L.)) were the predominant predatory birds which used bird perches frequently while predating on A. janata, S. litura and Conogethes punctiferalis (Guenee) larvae in BIPM and CIPM modules compared to non-IPM modules.

Kleptoparasitism is a tactic used to acquire food opportunistically and has been shown to provide several benefits, including greater food intake rate and the acquisition of items not normally available during self-foraging. Host individuals may differ in their ability to defend themselves against kleptoparasitic attacks and therefore identifying those host individuals that are particularly vulnerable to attack could both provide energetic benefits and increase the efficiency of kleptoparasitism as a foraging strategy. Here, we show that the kleptoparasitic fork-tailed drongo (Dicrurus adsimilis) specifically targets juveniles when following groups of cooperatively breeding pied babblers (Turdoides bicolor). Drongos give alarm calls upon sighting a predator, thus providing extra predator vigilance to foraging pied babblers. However, drongos also use alarm calls to steal food items. During kleptoparasitic attacks, drongos give false alarm calls and then swoop down to steal food items dropped by alarmed babblers. Juvenile pied babblers are particularly vulnerable to attack because they (a) spend a longer period handling prey items prior to consumption and (b) respond to alarm calls primarily by immediately moving to cover, in contrast to adults who respond by looking up and visually scanning the surrounding area. Drongos attack juvenile babblers significantly more often than adults, with attacks on juveniles more likely to result in the successful procurement of a food item. This patterns of attack suggests that drongos are able to differentiate between individuals of different age when targeting pied babblers, thus increasing the efficiency of kleptoparasitism as a foraging strategy.