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Bohol Sunbird - Male (Aethopyga decorosa)

Bohol sunbird (Aethopyga decorosa). This sunbird is found only in Bohol. Photo is from the flickr page of Neon Tomas Buenaflor Rosell II. Click image to go to his flckr photostream.

The Philippines is the center of diversity of sunbirds belonging to the genus Aethopyga.  The country boasts of 8 species, 7 of which are endemic. Now, a recent paper says that these numbers are conservative and that there should be at least 12 species that are all endemic to the country [1].

The authors examined 44 tissue samples from 15 of 18 Aethopyga sunbird species. Based on their genetic and morphological analysis, they have discovered that they can distinguish 21 species from their samples. They recommend resurrecting 5 species that are previously lumped into 2 species, and promoting 1 subspecies to a full species status. 

A. pulcherrima (metallic-winged sunbird), A. jeffreyi (Luzon sunbird), and A. decorosa (Bohol sunbird) are recommended to be resurrected as full species from being subspecies of A. pulcherrima. The Bohol sunbird will be the first vertebrate species endemic to the island. There are no other mammal, bird, fish, reptile or amphibian that “is currently considered a Bohol endemic.”

A. flagrans guimarasensis (maroon-naped sunbird) should be a distinct species, A. guimarasensis. It is recommended that it be separated from its close relative A. flagrans (flaming sunbird).

Aethopyga magnifica (magnificent sunbird) should have a species status as suggested by the author. Their analysis shows that it evolves separately and diverges from its continental Asian relatives long time ago.

12 sunbird species and their distribution across the Philippines. Color overlap means there are two or more species in those areas. This figure is my interpretation of the results in [1].  Click to enlarge.

12 sunbird species and their distribution across the Philippines. Color overlap means there are two or more species in those areas. This figure is my interpretation of the results in [1]. Click to enlarge.

Spotlight on Mindanao

In my point of view, the more interesting part of the paper is how the sunbirds made it to the Philippines and how they diversify.

The authors said that there maybe 3 or 4 separate events of colonization 2 to 5 million years ago. One event is the colonization of Palawan through Borneo of the ancestors of the present day A. shelleyi (lovely sunbird).

Another event is the colonization by the ancestors of the present day A. magnifica (magnificent sunbird) of the present day Panay, Negros and Cebu islands also through Borneo.

The third/fourth colonization happens through modern day Mindanao from Borneo. Their reconstructions suggests that “A. christinae (fork-tailed sunbird, a continental species) recolonized Asia from a Philippine ancestor, although support was weak and the results do not reject an alternative scenario in which A. bella (handsome sunbird) and the ancestors of the other 8 Philippine endemic sunbirds colonized the Philippines independently from continental ancestors.” 

It is not clear whether the ancestors of these 10 sunbirds evolved in Mindanao and A. christinae (fork-tailed sunbird) migrated back to continental Asia or two colonization happened wherein the ancestors of  A. bella (handsome sunbird) and A. christinae, and the ancestors of the 8 remaining birds separately colonized the Philippines thru Mindanao.

What is clear to the authors are 1) these remaining 8 endemics came from the same ancestors and 2) 4 of these sunbirds were products of evolutionary radiation in the mountains of Mindanao.

Some of these ancestors conquered other islands and Mindanao and “got isolated within islands, and across shallow- and deep-water barriers.” They evolved into present day A. pulcherrima (metallic-winged sunbird), A. jeffreyi (Luzon sunbird), and A. decorosa (Bohol sunbird), and A. guimarasensis (maroon-naped sunbird) and A. flagrans (flaming sunbird).

Some of these ancestors stayed in what is now central Mindanao. About 1.6 to 3 million years ago, the isolated mountains of central Mindanao started rising and became what the authors hypothesized as sky islands. The mountains separated one population of these sunbirds from another. These different isolated groups evolved into the present day A. primigenia (grey-hooded sunbird), A. linaborae (Lina’s sunbird), A. boltoni (apo sunbird) and A. tibolii (T’boli sunbird). These species occupy different areas except for A. primigenia and A. boltoni which overlap in Bukidnon. However, there is no sign of interbreeding between the two.

An avian (bird) radiation in a small island like Mindanao is UNIQUE. So far, only two other islands have similar radiation, Madagascar and New Guinea, according to the authors. Madagascar is a little over 6 times the size of Mindanao while New Guinea is a little over 8 times.

A detailed study of animals in Mindanao will most likely reveal more new species and new insights on animal migration and diversification in the country.

Reference:

[1] Hosner, P. A., Nyári, Á. S., & Moyle, R. G. (2013). Water barriers and intra-island isolation contribute to diversification in the insular Aethopyga sunbirds (Aves: Nectariniidae) Journal of Biogeography, 40 (6), 1094-1106 : DOI: 10.1111/jbi.12074

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