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From the introduction:
"[...] A strict separation into different species or subspecies of two geographically separated populations of similar birds is not straightforward. There is not one single criterion or one measure that would trigger a sharp taxonomic separation to tell us where a subspecies ends and a species starts. We are rather in the presence of a continuum where we have to judge and weight the differences found. Especially for bird populations that are geographically completely isolated from one another, it may be largely a matter of taste whether we confer species or subspecies rank to them.
In the family of grebes Podicipedidae, the situation is not different from that in other families of birds. For some members, geographically isolated subpopulations are treated as subspecies although we are not entirely confident that the locally evolved traits are perhaps sufficient for species rank. For others, the classification into allopatric subspecies has never been really challenged. The two studies presented in continuation now investigate the courtship rituals of recognized geographical subspecies of two species of grebes.
In the case of the Black-necked or Eared Grebe Podiceps nigricollis, the status of the three existing subspecies in North America, Europe and Africa is so far not subject to controversy and, in literature, minimal differences between them in coloration and size have been described. Possible behavioural deviations are however less clear as there is much cross-referencing in the description of their pair bonding displays and differences may perhaps remain masked. For the American and European subpopulations, the first study focuses largely on courtship as the pair bonding behaviour is critical to speciation. It aims at clarifying the rituals used by each subspecies and at identifying possible differences.
The second species analysed is the South American White-tufted Grebe Rollandia rolland. Also here, we are in the presence of three recognized subspecies. There is however much discussion of whether the much larger nominate form from the Falkland Islands should have a separate species' status from that of the two continental forms. Due to the remote location of the Falkland Islands, it is partially a lack of knowledge about the behaviour of their subspecies in comparison to that of the other two subspecies that prevents progress in the discussion. This study presents the first rather exhaustive description of Rollandia rolland rolland from the Falkland Islands and compares its ethology, including water and platform courtship, to the knowledge published about the subspecies from the South American continent.
Courtship in European Black-necked Grebe Podiceps nigricollis nigricollis and American Eared Grebe P. n. californicus
A comparative study with some notes on the displays in the African Black-necked Grebe P. n. gurneyi (pages 7-74)
The Falkland Islands’ White-tufted Grebe Rollandia rolland rolland (Quoy & Gaimard 1824)
Life history and comparison of its ethology to mainland White-tufted Grebes R. r. chilensis (pages 75-120)