Cacomantis Merulinus) Nestlings and Their Common Tailorbird (Orthotomus Sutorius) Hosts Odd Helge Tunheim1, Bård G

Tunheim et al. Avian Res (2019) 10:5 https://doi.org/10.1186/s40657-019-0143-z Avian Research RESEARCH Open Access Development and behavior of Plaintive Cuckoo (Cacomantis merulinus) nestlings and their Common Tailorbird (Orthotomus sutorius) hosts Odd Helge Tunheim1, Bård G. Stokke1,2, Longwu Wang3, Canchao Yang4, Aiwu Jiang5, Wei Liang4, Eivin Røskaft1 and Frode Fossøy1,2* Abstract Background: Our knowledge of avian brood parasitism is primarily based on studies of a few selected species. Recently, researchers have targeted a wider range of host–parasite systems, which has allowed further evaluation of hypotheses derived from well-known study systems but also disclosed adaptations that were previously unknown. Here we present developmental and behavioral data on the previously undescribed Plaintive Cuckoo (Cacomantis merulinus) nestling and one of its hosts, the Common Tailorbird (Orthotomus sutorius). Methods: We discovered more than 80 Common Tailorbird nests within an area of 25 km2, and we recorded nestling characteristics, body mass, tarsus length and begging display every 3 days for both species. Results: Plaintive Cuckoo nestlings followed a developmental pathway that was relatively similar to that of their well-studied relative, the Common Cuckoo (Cuculus canorus). Tailorbird foster siblings were evicted from the nest rim. The cuckoo nestlings gained weight faster than host nestlings, and required 3–9 days longer time to fedge than host nestlings. Predation was high during the early stages of development, but the nestlings acquired a warning display around 11 days in the nest, after which none of the studied cuckoo nestlings were depredated. The cuckoos’ begging display, which appeared more intense than that of host nestlings, was initially vocally similar with that of the host nestlings but began to diverge from the host sound output after day 9. Conclusions: The developmental data on Plaintive Cuckoo nestlings and their tailorbird host builds an important foundation for future work on the co-evolutionary interactions in this parasite–host system. Keywords: Avian brood parasitism, Coevolution, Cuckoos, Developmental biology Background tropics where the birds are difcult to observe and the Te cuckoo family, Cuculidae, is a phylogenetic group nests are well hidden. Hence, the majority of our knowl- of birds renowned for its large number of brood para- edge of brood parasitism has been acquired from inves- sites (40% of cuckoos). Te parasitic reproductive strat- tigations on a few species [particularly the Common egy has likely evolved independently three times in the Cuckoo (Cuculus canorus)] (Payne 2005; Stevens 2013). lineage (Payne 2005; Sorenson and Payne 2005). Many Recently, the focus has broadened to a wider range of cuckoo species are difcult to study, as they live in the host–parasite systems, which has strengthened some of the hypotheses derived from early studies and coun- *Correspondence: [email protected] tered others (Stevens 2013). In addition, diferent host– 1 Department of Biology, Norwegian University of Science parasite systems are at diferent stages as they respond to and Technology (NTNU), 7491 Trondheim, Norway various ecological selection pressures and hence follow Full list of author information is available at the end of the article © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/ publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Tunheim et al. Avian Res (2019) 10:5 Page 2 of 10 various co-evolutionary routes (Britton et al. 2007; Ste- not for Dunnocks (Prunella modularis), Robins (Eritha- vens 2013). Species in east and southeast Asia and New cus rubecula) and Reed Warblers (Noble et al. 1999) and Guinea are especially poorly studied, so explorations of gape-colored skin patches on the wings of Hodgson’s these systems may reveal novel deceptive traits (Stevens Hawk-cuckoo (Cuculus fugax) nestlings that simulate 2013). Te present study aims to shed light on a poorly additional gapes in the nest (Tanaka and Ueda 2005). studied host–parasite system in southwestern China that Here, we describe nestling development of the Plaintive includes the Plaintive Cuckoo (Cacomantis merulinus) Cuckoo and its Common Tailorbird host in southwestern (hereafter referred to as “cuckoo”), a small Asian cuckoo, China. Previous studies of this system examined adap- and one of its hosts, the Common Tailorbird (Orthoto- tations at the egg stage; the host has evolved dimorphic mus sutorius) (hereafter referred to as “tailorbird”). eggs that are mimicked by the cuckoo, and mismatched Many parasite nestlings eliminate host progeny, an cuckoo eggs are frequently rejected (Yang et al. 2016; adaptation that is energetically costly but that results in a Liang et al. 2017). Both species have two egg morphs, fea- monopoly of parental provisioning by the brood parasitic turing a ground color of either blue or white and spots nestling (Grim et al. 2009). For many cuckoo species, the that are brown or red. Within each tailorbird clutch, only elimination occurs by the cuckoo nestling evicting host one egg type is found. A recent study reported that the eggs and/or nestlings of the nest rim to certain death Plaintive Cuckoo does not always deposit eggs that match (Davies 2000). the host egg morph. Te result is a 50% mismatch of the Non-evicting brood parasites grow up alongside host host egg morph by the cuckoo, and such mismatches do nestlings and have to compete with them for parental lead to host rejection of the cuckoo egg (Yang et al. 2016). resources (Kilner et al. 2004). Te strategy of these nest- Te co-evolutionary interactions at the nestling stage in lings is to become stronger competitors that the parents this host–parasite system are, however, unknown (Payne will favor over their own young (Soler et al. 1995). As 2005). Te aim of this paper is therefore to describe the parents adjust their investment according to the num- behavior and collect developmental data of the Plaintive ber of nestlings in the nest, the presence of foster siblings Cuckoo nestling. Such knowledge will have fundamen- may reward parasites by positively afecting the number tal importance for further studies of this system and will of food loads that host parents bring to the nest (Kilner enable comparisons with other host–parasite systems. et al. 2004). By contrast, evictors face problems in assimilating suf- Methods fcient food, as host parents adjust their provisioning in Study area and study species response to the gape-area displayed in the nest. Even Tis study was conducted in and around the village of though cuckoo nestlings have a relatively large, con- Nonggang (22°30′N, 106°58′E), Guangxi Zhuang Auton- spicuous gape, it is far smaller than the area that would omous Region, in southwestern China. Te landscape is be covered by an entire brood (Kilner and Davies 1999). a mosaic of steep limestone peaks covered in dense veg- Terefore, the cuckoo nestling employs another set of etation amid cultivated fatlands. Te area is situated on adaptations to ensure that it will receive sufcient pro- the margins of the tropics with a mean annual rainfall of visioning: a set of exaggerated begging signals. A single 1150–1550 mm and a mean annual temperature of 20.8– Common Cuckoo nestling can mimic the sound output 22.4 °C (Yang et al. 2016). Te feldwork was performed of a whole brood of Reed Warblers (Acrocephalus scir- from April to June 2014. paceus) by day 6 or 7 after hatching, producing a beg- Te Common Tailorbird, an abundant species in the ging call that increases with age in frequency (Davies inhabited parts of the Nonggang area, is a common host et al. 1998; Kilner et al. 1999). Tereby, evictors are able for the Plaintive Cuckoo (Payne 2005; Yang et al. 2016). It to elicit sufcient amounts of food, as they normally are uses sturdy leaves from a variety of tree species to create of larger size than the selected hosts. In some brood- its nest, sewing one or two leaves together with organic parasitic systems, mimicry of the host nestling begging material (Fig. 1). Te result is a dome-shaped fundament call may also be a trait acquired to battle rejection by in which the tailorbird places its nest. Nonggang is on host parents (Langmore et al. 2003) or to convince host the northern boundary of the Plaintive Cuckoo’s distri- parents of nestling value to avoid desertion, as host par- bution range and this species migrates from its breeding ents may desert progeny that take an atypical long time areas in China to spend the winter in the more southern to fedge (Grim et al. 2003; Grim 2007). Other traits parts of its natural range (Payne 2005; Yang et al. 2012). have also been revealed to act as solicitation enhanc- Although some previous studies of the Plaintive Cuckoo ers, such as the colorful gapes of the Common Cuckoo have been conducted, the co-evolutionary interactions nestling that work as a supernormal stimulus for Rufous between the cuckoo and its tailorbird host have remained Bush Chats (Erythropygia galactotes) (Álvarez 2004), but largely unknown. Te Plaintive Cuckoo is a relatively Tunheim et al. Avian Res (2019) 10:5 Page 3 of 10 small cuckoo where females either look similar to males whereas the remaining eleven cuckoo nestlings were or appear in a reddish-brown “hepatic” morph (Payne translocated to new nests.

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