Response of Male Pied Bushchats Saxicola Caprata to Playback of the Songs of Neighbours and Strangers

Ornithol Sci 16: 141 – 146 (2017) ORIGINAL ARTICLE Response of male Pied Bushchats Saxicola caprata to playback of the songs of neighbours and strangers Navjeevan DADWAL# and Dinesh BHATT Avian Diversity and Bioacoustics Laboratory, Department of Zoology and Environmental Science, Gurukula Kangri University, Haridwar, Uttarakhand, India ORNITHOLOGICAL Abstract Discrimination between neighbours and strangers, on the basis of acoustic cues, has been clearly demonstrated in many temperate avian species, but experi- SCIENCE ments on neighbour-stranger recognition have received less attention in tropical habi- © The Ornithological Society tats, particularly in the Indian subcontinent. With this in mind, neighbour–stranger of Japan 2017 discrimination experiments were conducted on tropical male Pied Bushchats Saxicola caprata in the District Haridwar, of the Himalayan foothills, India. The sound levels of broadcasted songs were kept as close as possible to natural song levels. The results of the parameters analysed (including song rate, song repertoire, flights toward the speaker, distance from the speaker, and latency) did not differ significantly between neighbour and stranger song playbacks. It seems that male Pied Bushchats responded evenly toward the playback and may be incapable of discriminating between neighbours and strangers. Key words Neighbour, Pied Bushchats, Playback, Recognition, Stranger, Tropics Many animal species produce various acoustic Yasukawa et al. 1982; Stoddard 1990; Lovell & Lein signals that may influence the behaviour of their 2004; Hardouin et al. 2006; Wei et al. 2011) have receivers. The capacity of the receiver to interpret given similar explanations, with only a few excep- the sound signals is of substantial benefit because a tions (e.g. Lachish & Goldizen 2004; Courvoisier et given acoustic signal may carry a range of informa- al. 2014). tion depending on the status of the signaller, such as Recognition of a given acoustic signature relies on a neighbour, a stranger, a potential mate, an immature the receiver’s ability to recognize differences among or mature conspecific, or whether it is dominant or individuals with which it interacts repeatedly, an subordinate (Blumstein & Munos 2005). The abil- ability that is a basic necessity for signal identifica- ity of a receiver to detect the context and meaning tion. The intensity of a territory owner’s response of a given signal may allow it to estimate whether to a stranger is generally greater than that towards a potential territorial dispute involves a familiar or a neighbour (Temeles 1994) and is thought to mini- unfamiliar conspecific (Wilson & Mennill 2010). mize the costs associated with territory defence for Fisher (1954) was the first to explain reduced territory owners (Getty 1987). However, for most aggression towards territorial neighbours, describing songbird taxa recognition ability is variable and, for it as the “Dear enemy effect.” The relevance of such the most part, unexplored (Naguib & Todt 1998). acoustic cues has since been thoroughly studied in Much of our knowledge regarding territorial songbirds (Courvoisier et al. 2014). The ability of a behaviour and territorial defense by individuals, bird to distinguish between familiar and unfamiliar comes from research on temperate zone birds (Fedy conspecifics is primarily based on vocal clues. These & Stutchbury 2004). Few studies have examined clues may help to minimize the cost of aggressive neighbour-stranger recognition in tropical habitats, interactions in order to mediate social relationships especially among the birds of the Indian subconti- with neighbours. Most researchers (Wunderle Jr 1978; nent. In view of this gap in understanding, an attempt (Received 13 September 2016; Accepted 1 April 2017) was made to discover whether male Pied Bushchats # Corresponding author, E-mail: [email protected] Saxicola caprata, tropical closed-ended song learn- 141 N. DADWAL and D. BHATT ers with a known song repertoire size (Sethi et al. natural song repertoire size of the designed stimuli. 2011), are able to discriminate between neighbours Playback tracks were treated to reduce background and strangers songs in their natural habitats. noise while keeping the songs as close to their natural state as possible. After a thorough examination, only clear song samples were chosen for the play- MATERIALS AND METHODS back procedure and each playback was fixed to three This study was carried out during 2016 in the minutes. Playback tracks consisted of a song rate of natural habitat of the Pied Bushchat (bushes and 13.41±2.46 songs per minute, a song repertoire size scrubland) in Haridwar (29°55′N and 78°08′E), in of 7.68±2.7 per minute, a phrase gap (time inter- the Himalayan foothills of Uttarakhand State, India. val between two consecutive song types) of 2.7±0.5 Research was conducted during the peak of their seconds and a percentage performance time (actual breeding season, (June to July) when paired mates time for which males were vocally active during their were on established territories, in the early mornings response measurement) of 10.57±1.7 per minute. immediately after resident males had terminated their The loudness of the stimuli was kept similar to the daily dawn song delivery. natural loudness of Pied Bushchats. Although, we did The Pied Bushchat (Order Passeriformes, Family not measure the sound pressure level of the playback Muscicapidae) is a tropical songbird that occurs dis- stimuli, we adjusted the sound level of the broad- continuously from Transcaspia and the Indian subcon- casted playback to be as similar as possible to the tinent to South-East Asia, the Philippines, Indonesia, natural sound of the species. We examined whether New Guinea and New Britain. The breeding season songs were really sung in response to the sound play- is mainly from February to August with a peak from back or not by comparing the data of natural singing March to June. The Pied Bushchat is a bird of open spells and response during playback sessions (both cultivated landscapes, especially rice and sugar cane neighbour response and stranger response individu- fields. It is a resident breeder in tropical southern ally; Table 1). We performed a Mann-Whitney test to Asia from the Greater Middle East through Pakistan, check whether the response of the study individuals India and Bangladesh eastwards to Indonesia (Ali & was due to the simulated playback sessions or not. Ripley 2001). While keeping the time frame of all playback con- Twenty individuals with known song repertoires stant (0600 to 0700), playback songs were always were subjected to playback in their own territories. broadcast using a 10 meter cable attached to speak- Playback stimuli were designed under two catego- ers (Sony SRS x55; attached to a laptop) and a ries: neighbours and strangers (5 km away from all remote controlled control set up was placed within study sites) from the on-going breeding season. Play- 5-10 metres of the territorial edge, so as to avoid any back tracks were prepared from pre-recorded songs interference by the observers in the natural responses. matching the natural song rate of the Pied Bushchats. Playback was staged from the subject’s boundary Since Pied Bushchats are immediate variety sing- with the neighbour, whose songs were being used in ers (Sethi et al. 2011), we did not tamper with the the playback (on the neighbour’s side of the bound- Table 1. The compression of song rate and song complexity in natural singing sessions of Pied Bushchat versus neighbours and strangers. Song Natural Playback Playback Natural singing Natural singing Parameters singing sessions sessions sessions sessions sessions neighbour stranger vs. vs. (Mean±SD) response response neighbour stranger (Mean±SD) (Mean±SD) response response Mann-Whitney test (U-test) U=77.5, z=−2.67, U=77.5, z=−2.67, Song rate 14.6±1.8 9.8±2.4 8.9±3 P=0.007 P=0.007 U=116.5, z=−1.43, U=116.5, z=−1.43, Song complexity 11.01±2.86 6.4±3 5.5±2.1 P=0.15 P=0.15 142 Playbacks response of Pied Bushchats ary). We expected to obtain stronger responses from types per minute), percentage performance time (i.e. resident males by placing the speakers at the territo- the actual duration (subtracting the silence) for which rial edge, as indicated by Brooks and Falls (1975). a male was vocally active during response [(sum of Two trials were made, from the same locations, two all song durations×100)/total duration of singing ses- meters from the regular song perch of the resident sions]), phrase gap (time interval between two con- males (the distance from the subjects to the speakers secutive songs types), flights towards the speaker i.e. was same in each of the trails), in each territory with flights taken by a resident male towards the playback a five minutes gap between two consecutive play- setup, distance from the speaker i.e. the minimum backs to avoid habituation to playback. Of these two distance of a resident male from the playback setup trials, the one that achieved the best response was (speakers) and latency between stimuli and response considered for the analysis. The speakers were kept i.e. the time gap (minutes) between the start of play- parallel to the regular perch height (about 1.5 meters) back and the response of Pied Bushchats. of the resident males. The experiment was repeated The Wilcoxon signed rank test (Paired samples) for each individual with different stimuli after a ten- was used to calculate the difference between the day gap. various parameters across neighbour versus stranger The vocal responses of males were recorded with responses. Playback was carried out only during calm a Sennheiser ME 67 directional microphone attached weather. Song samples of male Pied Bushchats were to a Marantz PMD 670 digital sound recorder. Spec- recorded in the field without disturbing them.

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