Macro- and micro-evolution of avian bills

17 Feb 2017 - 18:04 -- Eduardo de Juana

Bill shape in birds is closely associated with diet and foraging techniques and is known to have a key role in avian adaptive radiations. Darwin’s finches of the Galapagos Islands are a good example of bill variation at a microevolutionary scale, within a limited geographical area and over a comparatively short period. But how has avian bill shape evolved across time to attain its outstanding current diversity? Three-dimensional scans of museum study skins, comprising over 2,000 species and over 97% of extant genera, give interesting results that support the well-known model of the paleontologist George Gaylord Simpson#R. The rise of modern birds from the late Cretaceous onwards apparently occurred in a rapidly changing world, coinciding with extensive ecological opportunity. This may have driven Simpsonian mega-evolution across adaptive zones, later giving way to smaller scale fine-tuning of the bill as avian diversity expanded across the globe. Insular adaptive radiations in passerine birds, for example in Malagasy vangas, Hawaiian honeycreepers and the aforementioned Galapagos finches, have provided some of the fastest rates of bill evolution, closely linked to ecological opportunity, suggesting that lineages radiating on isolated island archipelagos can explore morphological space independently of the global avifauna.

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Vangas and allies (Vangidae)

  • Small to medium-sized passerines varying considerably in morphology and plumage.
  • Madagascar, one species also in Comoro Islands.
  • Forest, scrub and thorn-scrub, plantations and wooded areas near forest.
  • 13-32 cm.
  • 21 genera, 40 species, 76 taxa.
  • 8 species threatened;
    none extinct since 1600.

Large Ground-finch (Geospiza magnirostris)


Geospiza magnirostris

Gould, 1837, Galapagos Islands.

Present species hybridizes rarely with G. propinqua on Genovesa; on Santa Cruz, large-scale hybridization with G. fortis thought to have...

Descriptive notes: 15–16 cm; 27–39 g. A large ground-finch with massive bill often as deep as it is long and appearing as deep as entire head, base of mandible thick and obvious, as is angle of cutting edge, and bill wide (particularly when...
figure, drawing, illustration of Large Ground-finch (Geospiza magnirostris)