Up to 46 races recognized in recent works, but status and distribution of several uncertain, and review of whole group long overdue. West Indian taxa glaucops, insularis and nigrescens formerly included in present species, now shown to be separate species, T. glaucops; some authors separate only glaucops, retaining other two races in present species. Form delicatula sometimes treated as a full species (with sumbaensis, meeki, crassirostris and interposita as races)#R#R#R; deroepstorffi likewise regarded by some as a full species#R#R#R, and one recent author#R made a further five species (though not without some reservations), i.e. furcata (with pratincola, contempta, hellmayri and tuidara as races), detorta, thomensis, punctatissima and bargei, but differences, e.g. more powerful feet, less compelling than claimed. Considerable variation in size and colour may be more individual than geographical in many continental and some island regions, with possibly expanding zones of intergradation, particularly in Europe. Nominate and guttata intergrade from Netherlands, Belgium and N & E France to Germany (Rhine Valley) and C Switzerland; nominate intergrades with affinis in region of S Egypt and N Sudan. Validity of many proposed races considered too doubtful to be upheld: in Europe, pusilla, kleinschmidti, kirchhoffi and hostilis merged with nominate, and rhenana with guttata; Malagasy hypermetra with African affinis; island populations everetti, kuehni, bellonae, lifuensis and lulu with widespread Australasian delicatula; Bahamian lucayana with pratincola; and, in Neotropics, Colombian subandeana with guatemalae, stictica with contempta, and hauchecornei and zottae with tuidara. Also, current separation of niveicauda from furcata (based on colour characters) and of guatemalae from pratincola (ranges in Central America not yet satisfactorily determined) perhaps doubtful, and continued acceptance of bondi may not be tenable; size and colour variation in Neotropics in need of reassessment, and separation of hellmayri from tuidara based on size characters questionable. Furthermore, poensis possibly not separable from affinis, in which case older name poensis has priority. N African population currently included in nominate is sometimes placed in erlangeri; birds from S Myanmar to Indochina sometimes placed in javanica, but seem better included in stertens. Melanesian populations, currently covered by three races (delicatula, crassirostris, interposita), may merit further splits. Twenty-eight subspecies currently recognized.
Introduced (affinis) to Seychelles and (delicatula, pratincola) to Lord Howe I, where now presumed extirpated (few records since 1970s considered vagrants), and (pratincola) to Hawaii.
Food and feeding
Status and conservation
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