Discerning the presence of Thrush Nightingale (Luscinia luscinia) among Common Nightingale (Luscinia megarhynchos) Rozlíšenie prítomnosti slávika veľkého (Luscinia luscinia) medzi slávikmi obyčajnými (Luscinia megarhynchos) Michael BLAIR 7 Bryony Court, Holt, Norfolk, NR25 6AF, United Kingdom; [email protected] In many cases, Thrush Nightingale Luscinia back and brighter rufous in the primaries and luscinia and Common Nightingale Luscinia the rump tended to have a longer area of rufous. megarhynchos sing from concealment, but Chest markings on individuals were inconclu- may sing from exposed branches during the sive. All birds seen resembled more closely day (Snow & Perrins 1998). The former has those illustrated in Mullarney et al. (2001) than a breeding distribution (Bogucki & Sorjonen those in Snow & Perrins (1998), yet the Thrush 1996, Mošanský & Danko 2002) largely north Nightingale illustrated in Mullarney et al. and east of the latter (Grüll & Fracasso 1996), (2001) is in autumn plumage! Some individual but has experienced a westward spread in central plumage variation was noticeable in Common and eastern Europe since the 1970s (Bogucki Nightingale. Although hybridisation is known, & Sorjonen 1996). There has been no corre- it may be limited to male Thrush Nightingales sponding retreat in the area of overlap of the at the limit of range expansion mating with fe- breeding distribution of Common Nightingale male Common Nightingales. The male offspring (Grüll & Fracasso 1996), which means in a are sterile and the female fertile (Bogucki & widening zone of sympatry, bird survey wor- Sorjonen 1996), which may help restrict ge- kers and birdwatchers can expect to encounter ne-flow and minimise numbers of hybrids. It both species in areas where once only Common would scarcely be a surprise if Euring records Nightingale could be found. Many popular bird revealed a surprising number of ‘wanderers’ to books still show only an outdated distribution western Europe, but even in the area of expan- of Thrush Nightingale in this region of Europe sion, ringing results are constrained by the rin- (Mullarney et al. 2001). In places, the breeding ging effort that can be deployed and by ringing range expansion of Thrush Nightingale may priorities. However, despite the difficulties, it is be linked to a reduction in livestock farming, often possible to confirm the presence of Thrush allowing encroachment of dense bushes that Nightingale among Common Nightingale popu- comprise primary habitat (Koskimies 1989). lations, through careful listening to song and by Clearly, the best way of confirming the identifying the singing bird, particularly when identity of Thrush Nightingale is in the hand singing is at its most intense during the early of a ringer, but those individuals encountered part of the breeding season. in Slovakia had a greyish back and inner wings, The advent of bird species’ songs and calls muted rufous tinge to the dark primaries and a on memory cards fitted to pocket personal rufous rump. They were altogether greyer and computers, in this case a Hewlett-Packard iPAQ lacking the dull rufous ground colour usually Personal Digital Assistant (PDA) containing seen. Perhaps the strong sunlight of the 2007 the Collins e-Guide (Mullarney et al. 2006), spring had accelerated plumage fading. The allows the bird survey worker or birdwatcher nominate Common Nightingales had a rufous to attune to the aural memory, or to refresh it Tichodroma 20 (2008) 167 in the field while listening to the bird singing. bordering the road that runs across the north People with both a good aural memory and a of the park. The sound of so many Common good sense of musical pitch are at an advantage Nightingales quite obscured any noise other here. Unfortunately, many keen ornithologists common songbirds might be making, but Thrush or birdwatchers lack to a varying degree one Nightingale could be distinguished, and very or other of these abilities, the latter condition occasionally I was able to see an individual known popularly as having a ‘tin ear’. From clearly. However, there was a lesson to be learnt mid-May to mid-June 2007, while carrying here – the songs of Common Nightingales so- out bird survey work for the Institute of Forest metimes varied between individuals, not only Ecology SAS, Zvolen, Slovakia, we (a group in content, but also in ‘sweetness’ and ‘har- of nine people from the Royal Air Force shness’ – in other words, different individuals Ornithological Society) had the opportunity to had different ‘voices’. The problem was that a note the behaviour and interactions of many bird Common Nightingale singing in a ‘voice’ that species. The first part of the survey was in the lacked ornamentation could not always be di- Ipeľ valley, working eastwards from Šahy (close stinguished for certain each time it sang from a to the Hungarian border, in southern Central nearby Thrush Nightingale. It may be that when Slovakia). Drought had hit the area in winter singing Common Nightingales are at a high and spring – the rivers and streams were low, density, variation in individual songs may be the spring cereals had died in many places, the one way for a female to pick out one male from grasslands were parched (most lacked Yellow another, but we must bear in mind that what a Wagtails Motacilla flava entirely) and the day human ear hears in terms of note-repetition rate temperatures reached 34 ºC. The corollary and harmonic variation is not what a bird hears. was that many species, including Common I have also heard considerable ‘voice’ variation Nightingale, appeared to have concentrated amongst individual Common Nightingales in along the banks of the River Ipeľ in the trees, central Turkey in suitable habitat created by bushes and undergrowth. local irrigation schemes in narrow valleys. In previous years, I have visited locations In response to my questions, researchers where there were good populations of Common at Biologische Station Illmitz in eastern Nightingale and where Thrush Nightingale was Austria told me in 2006 of occasional Thrush also present. Amongst the lakes and waterways Nightingales trapped there in good breeding just southwest of Berlin, I was able to compare condition. I had asked the question because I the songs of the two species, and also to see the believed I had heard one singing amongst the individual birds as they sang. In this location, trees there, although I did not see it. Lastly, when the species’ songs clearly differed, the Common in Cyprus in March 2002, I heard a call from Nightingale’s having much more variation and thick undergrowth below the Asprokremnos usually beginning with much more ‘introduc- Dam. To me, it sounded different from the tory’ material. It was useful to be able to see calls of the migrant Common Nightingales. the plumage colour differences in good light, Eventually the bird, overall very dull rufous the Thrush Nightingale being very much duller in appearance, flew across the valley. Shortly indeed on its upperparts, except for the rufous afterwards, a short burst of song convinced rump, which contrasted strongly. I understand other birdwatchers, and eventually it was seen that the species had first been noted there in the clearly, a Thrush Nightingale. early 1990s (Klaus Witt, pers. comm.). In Slovakia, there is a known regular bree- On several visits to the Hortobágy Nemzeti ding area in the Eastern Slovakia (Mošanský & Park in eastern Hungary from 1995 onwards, Danko 2002), and irregular breeding attempts I found Thrush Nightingale in small num- were recorded also from western Slovakia bers amid a dense population of Common (Kaňuščák & Kočí 2002). However, breeding Nightingale in a tract of immature wet woodland data are missing from central part of the coun- 168 Tichodroma 20 (2008) try. During our survey work in the Ipeľ valley notes, but when Common Whitethroat Sylvia in 2007, I therefore listened attentively to the communis arrives, the latter’s scratchy song, nightingale ‘voices’. Once again, I could hear I would suggest, is the origin of harsher notes a wide variation in the Common Nightingale in the Dunnock’s song. Mimicry is an innate ‘voice’, although in the majority of cases, the ability of many bird species, but species-by-spe- song strongly resembled that on our PDAs. cies extent of mimicry varies, Marsh Warbler Nevertheless, on a number of occasions, per- Acrocephalus palustris being the ‘expert’, with haps a dozen, there seemed to be something over 200 species recorded (Snow & Perrins very distinct indeed, and I investigated as best 1998). To my ears, many species incorporate I could, thick undergrowth and foliage and also mimicry to a slight degree, and some mimicry the international border (with Hungary) permit- by Thrush Nightingale has been reported, for ting. On two occasions, the only bird seen was example from Armenia (del Hoyo et al. 2005), a Common Nightingale, but unfortunately, not but I am not aware of any cogent overview in during song. On perhaps four occasions, no bird the literature of the extent to which Thrush was seen, or was seen insufficiently well for any Nightingale and Common Nightingale do so, decision. On six occasions Thrush Nightingale although it is known that they will respond to was seen, although on three of those, a Common each other on occasion (Snow & Perrins 1998) Nightingale was within 10 metres. On three of – I have noted this inter-species behaviour those six occasions, the Thrush Nightingale sang previously, but could confirm it only twice in or called, the best being east of the hamlet of Slovakia. Peťov (May 18, 2007, N 48º07΄, E 18º30´), be- side the embankment to the former road bridge Súhrn into Hungary, where two Thrush Nightingales were competing from the tops of adjacent bu- Počas monitoringu vtáctva v údolí rieky Ipeľ v shes, below us.