Avian Brood Parasitism in South Asia 103
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PRAVEEN & LOWTHER: Avian brood parasitism in South Asia 103 Avian brood parasitism in South Asia Praveen J & Peter Lowther Praveen, J., & Lowther, P., 2020. Avian brood parasitism in South Asia. Indian BIRDS 16 (4): 103–119. Praveen J, Villa #5, Embassy Homes, Mudavanmugal, Poojappura P.O. Thiruvananthapuram, Kerala, India. E-mail: [email protected] [Corresponding author] Peter Lowther, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL, 60606, USA. E-mail: [email protected] Manuscript received on 14 August 2020. Abstract Brood parasitism is an evolutionary adaptation in which certain species, known as brood parasites, have evolved to use other species, known as hosts, to rear their young. While a lot of work to identify host species from India and South Asia has been based on egg collections from the first half of the twentieth century, this has not been followed up with extensive field studies except for certain species. Here we compile information from published literature, online websites, and social media to appraise the current knowledge in this topic, specifically focusing on documentation of hosts feeding parasites. We created an online catalog of 287 instances of host-parasite pairs, covering 15 of the 18 species of brood parasites, across 46 host species. The most commonly observed brood parasite pair is the House Crow-Asian Koel, followed by Argya babblers with Pied Cuckoo, and Common Hawk Cuckoo. We add ten new host-parasite pairs for South Asia, nine of them new to science. Our work did not find any hosts for Chestnut-winged Cuckoo, Whistling Hawk Cuckoo, and Himalayan Cuckoo from South Asia. We dedicate this work to Vijay Cavale (1961–2020) who inspired Indian bird photographers to share their work online. Introduction where the hosts were documented accompanying, or even Brood parasitism is a fascinating feature of avian biology. In feeding, an identifiable chick of a parasite. In that respect, we this evolutionary adaptation, certain species, known as brood trawled online image portals (Macaulay Library, iNaturalist, and parasites, lay their eggs in the nests of other species, known as Oriental Bird Images), and social media groups (Facebook) to hosts, which then rear the parasitic young, and serve as foster find reliable evidences for host-parasite behavior. In addition, parents. These birds incubate the parasite eggs along with their a short online survey was circulated to collate such instances own, and when the parasite egg hatches, they feed the young, from the public. We downloaded data up to and including June more often than not at the cost of their own reproductive success. 2020, from eBird, for all cuckoo species, filtered out records with In South Asia, brood parasitism is restricted to several species of species comments, and manually went through the comments cuckoos (Cuculidae: Cuculinae), and one species of honeyguide for records without relevant media. This altogether resulted in a (Indicatoridae). catalogue of 287 host-parasite entries after removing duplicates Historically, the documentation of avian brood parasitism in [See Supplementary File], most of them (~89%) from the past South Asia primarily followed identification of eggs in clutches decade. We have attempted to include cases where a specimen, (Hume 1890; Baker 1906a,b, 1907a,b, 1934, 1942). However, or a photograph, exists as documentation of the host-chick pair, or this method was not without its flaws as identification of cuckoo at least field notes that are clear. Additionally, where identification species from their eggs is fraught with difficulties. Becking of either the host or the parasite is straightforward, we also (1981) pointed out the dubious nature of egg identification depend on the reliability of the observer for correct identification. in Baker’s egg collection, and his host-parasite assignments. In all cases of host-parasite pairs, we qualify the observation by Becking, additionally, analysed the eggs using scanning electron the highest evidence type that is available: (S) studies published, microscopy and biochemistry techniques to identify hosts and (M) supporting media and (O) field observations. While general parasites. He also pointed out that not all hosts are viable for the references on this topic cover the species’ entire range (Payne parasite and some eggs would never hatch, and if they indeed 2005; Erritzøe et al. 2012), or are outside South Asia (Yang et do, the chick may not survive. Hence, he suggested that future al. 2012), we list references only if specific documentation was workers should let the cuckoos fledge and study them rather made within South Asia. For common parasite-host pairs, we do than collect the eggs and clutch. not provide exhaustive lists of all references, but limit them to Baker’s ornithological work, most particularly his egg collection, extensive studies. Secondary references like Ali & Ripley (1987) has been a source of controversy that makes it difficult to accept or Billerman et al. (2020) do not augment the information and his collections as the sole evidence for any ornithological discovery hence are not cited specifically. We do not use the list of host/ (see Walters 2006; Rasmussen & Anderton 2012). While Becking victim species from Baker (1942) as definitive but include its taxa (1981) made a substantial contribution in clarifying the air, we only for completeness. take this opportunity to supplement and establish norms and It is worth defining two terms used in brood parasitism. Those exceptions using the best available and latest information. species known to have received a parasite egg in their nests, but are not necessarily known to have reared the parasite young Methodology we term victims. Species that we term hosts are those victims We depart from the traditional methodology of host-parasite known to have reared a parasite young successfully (see also assignment using egg collection, and list only those instances Johnsgard 1997). A brood parasite host table, based solely on 104 Indian BIRDS VOL. 16 NO. 4 (PUBL. 18 SEPTEMBER 2020) eggs/clutches, is only capable of identifying victims, though many map is not representative for those areas, however, it is clear victims (unproven hosts) may eventually turn out to be true hosts that the eastern Himalayas have the highest diversity of brood as more observations and studies accumulate. Victims are easily parasites, followed by the western and central Himalayas, the identified during a single visit to a nest containing the parasite Western Ghats, and Sri Lanka. egg (s) or young; however, identifying hosts require follow up In this paper, we cover seventeen species of cuckoos, and visits to verify successful rearing of the parasite young. It may be one species of honeyguide occurring in our region with tables and mentioned here that Baker’s (1942) is, essentially, a victim list and maps where warranted. The centroids of the districts are overlaid not a host list. Through this work, we attempt to circumvent this on the distribution maps downloaded from State of India’s Birds problem by bringing in cases where hosts were recorded feeding (https://www.stateofindiasbirds.in/). We do not include the the young parasite. Our method too is not flawless, as many of vagrant Horsfield’s Bronze Cuckoo Chrysococcyx basalis. the host-parasite documentations are made opportunistically, and do not assert the parasite young to have been successfully raised Results by the attending adult, but it is a step in that direction. A caveat worth remembering here are the rare cases where certain non- Chestnut-winged Cuckoo Clamator coromandus host species may offer parental care, at least temporarily, masking This is a monotypic cuckoo breeding in the Himalayan and north- the true host from the observer (Sealy & Lorenzana 1997). There eastern Indian foothills, and wintering in Sri Lanka and south- is one such case from our region where a Grey-bellied Cuckoo western India. Laughing-thrushes of the genera Grammatoptila, Cacomantis passerinus raised by sunbirds (Nectariniidae) was Garrulax, Pterorhinus, and Trochalopteron are considered its also actively fed by Common Tailorbirds Orthotomus sinensis host species. However, no documentation from our region (Suter 1945). Misguided courtship, by adult cuckoos towards exists of any host species feeding a young Chestnut-winged juveniles, has also been reported in a few species (Kuriakose Cuckoo. The only direct observations of brood parasitism were 2012; Waiker & Sivanandan 2020). of a Chestnut-winged Cuckoo that was ‘noosed’ over a nest of Cuckoos are widely distributed in South Asia but regional a Lesser Necklaced Laughingthrush G. monileger, which it was diversity and abundance varies a lot. Based on eBird data presumably visiting to drop its egg and, that of a bird that was uploaded up to (and including) June 2020, the diversity shot as it left a nest of the same laughingthrush species (Baker (=number of species of brood parasites) and abundance 1907a). Based on Baker’s egg collection, Becking (1981) listed (frequency as percentage of complete lists that has at least one the Greater Necklaced- P. pectoralis and the Lesser Necklaced brood parasite) in South Asia is shown in Fig. 1 at a square with Laughingthrushes as common hosts, followed by the Striated resolution of 0.5° x 0.5° [c.56x56 km]. Squares with less than Laughingthrush G. striata, Rufous-vented Laughingthrush±1 P. 10 complete lists are omitted for frequency analysis. Admittedly, gularis, Blue-winged Laughingthrush T. squamatum, and Grey- there is insufficient eBird coverage in Afghanistan, Pakistan, and sided Laughingthrush P. caerulatus. This list is likely to be correct certain parts of east-central and northern India, and hence the based on Becking’s extensive laboratory studies. Fig. 1. The number of species and frequency of occurrence (as percentage of complete lists) of brood parasites in South Asia at square size 0.5° x 0.5° [c.56x56 km]; generated from data download from www.ebird.org/india.