Floreana Island, one of the islands in the Galápagos archipelago, is home to the critically endangered Medium Tree Finch (Camarhynchus pauper). This small passerine coexists and hybridizes with the common Small Tree Finch (C. parvulus). Estimating the population sizes of these species is extremely difficult because they are morphologically similar. Therefore, Katharina Peters and Sonia Kleindorfer relied on acoustical surveys. In other words, they compared the songs of these finches.
Song differed significantly between Medium Tree Finch and Small Tree Finch, but it was not possible to discriminate between Small Tree Finch and the hybrids. So, the latter two were combined in the ‘C. parvulus/hybrid’ group for further analyses.
Comparing acoustical surveys in 2004, 2008 and 2013, it turned out that the endangered Medium Tree Finch has declines by 52% between 2004 and 2013, while the ‘C. parvulus/hybrid’ group has increased by 45% during that time period. The decline of the Medium Tree Finch is probably the outcome from an extreme drought event that hit the Gálapagos islands from 2003 to 2007.
Peters, K. J. & Kleindorfer, S. (2017). Avian population trends in Scalesia forest on Floreana Island (2004-2013): Acoustical surveys cannot detect hybrids of Darwin’s tree finches Camarhynchus spp. Bird Conservation International, 1-17.
This paper has been added to the Thraupidae page.