Polymorphism in egg coloration is prominent in the Common Cuckoo (Cuculus canorus) and a common host, the Ashy-throated Parrotbill (Paradoxornis alphonsianus). Egg polymorphism has probably evolved as a consequence of frequency-dependent selection in both host and parasite, and has, according to human vision, resulted in discrete immaculate white, pale blue and blue egg phenotypes within a single population. However, egg mimicry assessment is not always straightforward, and previous studies have shown that human based comparisons applied to the coloration of bird eggs may be inadequate. Here, we objectively quantify egg color of both parasite and host by spectrophotometry and assess egg mimicry of the Common Cuckoo to the eggs of its Ashy-throated Parrotbill host. Our results revealed that egg reflectance spectra agree well with the assessment based on human vision that cuckoo eggs mimic those of the parrotbill host, in both visible (VIS) and ultraviolet (UV) ranges. However, the white cuckoo egg shows slightly poorer mimicry than the blue cuckoo egg in corresponding host clutches. We suggest that the white parrotbill egg morph (and subsequently the whitish cuckoo egg color) may have evolved after the evolution of the blue egg morph due to strong selection from parasites in the cuckoo-parrotbill system.
The Sociable Lapwing (Vanellus gregarius) was recently up-listed to Critically Endangered in the IUCN Red List of globally threatened species due to a large historical and presumed recently precipitous decline, as well as its globally very small population size (BirdLife International, 2009).
Its breeding distribution is nowadays restricted to the steppes of Kazakhstan and adjacent areas of Russia east of the Volga River. In Ukraine, the species became extinct around 1905, in European Russia probably in the 1980s (Dolgushin, 1962; Belik, 2005). Western populations of the Sociable Lapwing migrate through the Caucasus and Middle East, wintering in Israel, Iraq and NE Africa, whereas breeders from the eastern range probably depart via S Kazakhstan, Uzbekistan and Afghanistan and winter in northern India and along the coast of Pakistan (Delany et al., 2009).
So far in China, there has been only one known record in the eastern part of the country: Jesper Hornskov and others observed a single bird migrating northwards with a large flock of Grey-headed Lapwings (Vanellus cinereus) in September 1998 at Shijiutuo ("Happy Island"), Hebei Province (BirdLife International, 2001). The Sociable Lapwing was neither included in the first Chinese checklist (Swinhoe, 1871), nor in any of the following comprehensive publications on the Chinese avifauna (e.g. Cheng, 1976; Mayer de Schauensee, 1984; Cheng, 1987; MacKinnon and Phillipps, 2000; Zhang, 2000), but Zheng (2005) listed the species as a vagrant. An undocumented and possibly erroneous record from Xinjiang is listed in Ma (2001), based on Sudilovskaya (1936). The species was considered a rare migrant in Xinjiang before 1980, but there is obviously no documentation available for any of those records (Ma, 2007, personal communication).
Observations
A literature survey of historical sightings of Sociable Lapwing was undertaken to identify key wintering areas and migration routes within the framework of the international Sociable Lapwing research and conservation project. A review of German literature included reports and historic publications from German ornithologists A.E. Brehm and O. Finsch. Both participated in an expedition to Western Siberia that also visited the Chinese province of Ili-Tarbagatai (today known as the District of Tacheng, Xinjiang Uighur Autonomous Region) in the year 1876. According to notes in Brehm's diary (unpublished, parts available in Gensichen, 1982), breeding of the Sociable Lapwing was observed at the "Burgusutai Tscheku" plateau, 75 km east of the settlement Chuguchag (today Tacheng or Qoqek, 46°45′N, 82°57′E; Fig. 1). On 24 May 1876, Brehm noted: "We saw only the typical steppe species: Little Bustard, Demoiselle Crane, Sociable Lapwing and larks (…)". Later, Finsch (1879) added details from the same area: "We saw sometimes (…) Sociable Lapwings, which now had chicks (...)". The habitat is described as a short-grass steppe, grazed by domestic animals and thus already suggesting the same habitat preferences as currently observed (Kamp et al., 2009).
Figure
1.
Location of the 1876 Chinese breeding record at "Burgusutai Tscheku" east of Chuguchak, today Tacheng (Qoqek), Xinjiang Uighur Autonomous Region, P.R. China after A.E. Brehm (unpublished) and Finsch (1879). Historical records and the currently occupied easternmost breeding sites in eastern Kazakhstan are given as white squares (with years of last observations), scaled by colony size (source: Sociable Lapwing project database). The route of the German expedition is plotted as dashed line.
Both A.E. Brehm and O. Finsch were leading ornithologists of their time and had excellent knowledge in species identification. From earlier observations in Western Siberia during the same expedition they were familiar with the Sociable Lapwing (descriptions of breeding colonies near Omsk, Russia and in eastern Kazakhstan), thus there is no doubt that the species was identified correctly. The observation of chicks at the end of May clearly indicates successful breeding.
The nearest known breeding colonies of the Sociable Lapwing in Kazakhstan were situated approximately 60 km to the north of the Chinese breeding site in the late 19th century in the Chilikty valley (Finsch, 1879; Plotnikov, 1893; Fig. 1). It remains unclear, if there was much contact between a Chinese subpopulation and the Kazakhstan breeding birds, since the two sites are separated by the Tarbagatai mountain range (maximum altitude 3816 m a.s.l.).
Since the Xinjiang region is covered only by a very small number of ornithologists, it is not clear, if the Sociable Lapwing still breeds in western China. Ma (2007, personal communication) could not find the species during regular surveys conducted since the 1980s (Ma and Kraaijeveld, 2000). The closest currently known colonies are situated about 320 km northwest of the historical Chinese site (Nikolaevka, East Kazakhstan district; our own observations by J. Kamp and R.D. Sheldon, 2008). The species has not been recorded breeding in the Lake Zaisan area since the 1970s, despite intensive surveys (Berezovikov et al., 1999; Fig. 1). This, and the fact that the Sociable Lapwing vanished from the eastern parts of its wintering range in India's provinces Bihar and Uttar Pradesh already at the beginning of the 20th century (BirdLife International, 2001) suggests an early range distraction at the eastern edge of the distribution range. The reasons for the possible extinction in Xinjiang are unknown, but might be linked to changes in spatial grazing patterns of domestic and wild ungulates or a transformation of grassland into cultivated areas (Kamp et al., 2009). Land use changes in the wintering areas (probably on the Indian subcontinent) might have affected the easternmost breeding populations as well.
In conclusion, we suggest that the Sociable Lapwing should be treated as a possibly extinct breeder, today vagrant in China. However, surveys should be undertaken in the Xinjiang region to determine the status of the Sociable Lapwing in what should be considered the former breeding range of this species.
Acknowledgements
The Sociable Lapwing project is funded by the Darwin Initiative of the UK government and the Royal Society for the Protection of Birds (RSPB), with additional support from Swarovski optics, The Rufford Foundation and Deutsche Ornithologen-Gesellschaft (DO-G). We want to thank Jesper Hornskov, Ming Ma, Suhel Quader and John Fellowes for hints to important references and various support. Comments by an anonymous reviewer greatly improved the manuscript.
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