Tag: birds

What is a species? British bird expert develops a math formula to solve the problem

Two different kinds of Lachrymose Mountain-Tanager (Anisognathus lacrymosus) occurring in Colombia on different mountain ranges (left: Santa Marta; right: Yariguies). Their measurements and songs were as distinct as those in the group which co-occur. Therefore, they can therefore be treated as different species.

Nature is replete with examples of identifiable populations known from different continents, mountain ranges, islands or lowland regions. While, traditionally, many of these have been treated as subspecies of widely-ranging species, recent studies relying on molecular biology have shown that many former “subspecies” have in fact been isolated for millions of years, which is long enough for them to have evolved into separate species.

Being a controversial matter in taxonomy – the science of classification – the ability to tell apart different species from subspecies across faunal groups is crucial. Given limited resources for conservation, relevant authorities tend only to be concerned for threatened species, with their efforts rarely extending to subspecies.

Figuring out whether co-habiting populations belong to the same species is only as tough as testing if they can interbreed or produce fertile offspring. However, whenever distinct populations are geographically separated, it is often that taxonomists struggle to determine whether they represent different species or merely subspecies of a more widely ranging species.

British bird expert Thomas Donegan has dedicated much of his life to studying birds in South America, primarily Colombia. To address this age-long issue of “what is a species?”, he applied a variety of statistical tests, based on data derived from bird specimens and sound recordings, to measure differences across over 3000 pairwise comparisons of different variables between populations.

Having analyzed the outcomes of these tests, he developed a new universal formula for determining what can be considered as a species. His study is published in the open-access journal ZooKeys.

Essentially, the equation works by measuring differences for multiple variables between two non-co-occurring populations, and then juxtaposing them to the same results for two related populations which do occur together and evidently belong to different “good” species. If the non-co-occurring pair’s differences exceed those of the good species pair, then the former can be ranked as species. If not, they are subspecies of the same species instead.

The formula builds on existing good taxonomic practices and borrows from optimal aspects of previously proposed mathematical models proposed for assessing species in particular groups, but brought together into a single coherent structure and formula that can be applied to any taxonomic group. It is, however, presented as a benchmark rather than a hard test, to be used together with other data, such as analyses of molecular data.

Thomas hopes that his mathematical formula for species rank assessments will help eliminate some of the subjectivity, regional bias and lumper-splitter conflicts which currently pervade the discipline of taxonomy.

“If this new approach is used, then it should introduce more objectivity to taxonomic science and ultimately mean that limited conservation resources are addressed towards threatened populations which are truly distinct and most deserving of our concern,” he says.

The problem with ranking populations that do not co-occur together was first identified back in 1904. Since then, most approaches to addressing such issues have been subjective or arbitrary or rely heavily upon expert opinion or historical momentum, rather than any objectively defensible or consistent framework.

For example, the American Herring Gull and the European Herring Gull are lumped by some current taxonomic committees into the same species (Herring Gull), or are split into two species by other committees dealing with different regions, simply because relevant experts at those committees have taken different views on the issue.

“For tropical faunas, there are thousands of distinctive populations currently treated as subspecies and which are broadly ignored in conservation activities,” explains Thomas. “Yet, some of these may be of conservation concern. This new framework should help us better to identify and prioritize those situations.”

Two different kinds of Three-striped Warblers (Basileuterus tristriatus) occurring in South America (left: East Andes of Colombia; right: a recently discovered population from the San Lucas mountains of Colombia). Note the differences in plumage coloration. While somewhat differing in voice, plumage and some measurements, the couple did not diverge as much as other related warblers that actually co-occur did. These are about as close as subspecies occurring on different mountain ranges could be. However, they marginally failed the proposed new benchmark for species rank.

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Original source:

Donegan TM (2018) What is a species? A new universal method to measure differentiation and assess the taxonomic rank of allopatric populations, using continuous variables. ZooKeys 757: 1-67. https://doi.org/10.3897/zookeys.757.10965

Additional information:

Donegan’s proposals were first presented orally at a joint meeting for members of the Neotropical Bird Club, British Ornithologists’ Club and Natural History Museum in London.

New immigrant: Shiny Cowbirds noted from a recording altitude of 2,800 m in Ecuador

Two juveniles of Shiny Cowbird, a parasitic bird that lays its eggs in the nests of other birds, were spotted in the Andean city of Quito, Ecuador, for the first time. This finding represents an altitudinal expansion of approximately 500 m.

Breeding populations might have been prompted by forest fragmentation and/or climate change, suggest the research team, led by Dr Verónica Crespo-Pérez, professor at Pontificia Universidad Católica del Ecuador (PUCE). Resultingly, the ‘immigrants’ could be threatening native birds. The study is published in the open access Biodiversity Data Journal.

“The Shiny Cowbird is native to the lowlands of South America but within the last 100 years, it has been expanding its distribution to higher altitudes and latitudes” says the lead author.

The bird had already been noted from high altitudes in Bolivia and Perú, and in some localities in the Ecuadorian Andes. Since 2000, Juan Manuel Carrión, co-author and director of the Zoo in Quito, recalls observing Shiny cowbirds near his home in a valley near Quito at 2,300 m above sea level (asl). However, one has never before been reported from an altitude as high as 2,800 m asl.

Moreover, the fact that the observed individuals were juveniles means that the species is already breeding in the city.

“Such a significant expansion of reproductive birds, of approximately 500 m, could be related to human disturbances, like forest fragmentation or climate change,” adds Crespo-Pérez.

The observations took place at the PUCE campus about a year ago. Two juvenile Shiny cowbirds were seen parasitizing two different pairs of Rufous-collared Sparrow, one of the most common birds in Quito. The cowbirds displayed food-begging behaviors to adult sparrows, including chasing the sparrows on the ground and chanting intensely on bushes and tree branches.

“These observations mean that the birth mother of the cowbird laid her eggs in the nests of the sparrows, who inadvertently, became the cowbird’s foster parents and incubated, fed and cared for the it as if it were its own, even though the cowbird is almost twice as big,” says Miguel Pinto, co-author and professor at Escuela Politécnica Nacional, and former postdoctoral fellow at the Smithsonian Institution.

“The sparrows were not feeding fledglings of their own species, which suggests that the Cowbird could be having some negative effect on the Sparrow, at least on their ability to reproduce,” points out Tjitte de Vries, co-author and professor at PUCE.

There are several published reports of negative effects of Cowbirds on other birds, especially on species that are already endangered or have restricted distribution ranges. Therefore, this report of an expansion of the Shiny Cowbird towards higher altitudes may be of concern, mainly for native, endemic or endangered bird species.

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Original source:

Crespo-Pérez V, Pinto C, Carrión J, Jarrín E R, Poveda C, de Vries T (2016) The Shiny Cowbird, Molothrus bonariensis (Gmelin, 1789) (Aves: Icteridae), at 2,800 m asl in Quito, Ecuador.Biodiversity Data Journal 4: e8184. doi: 10.3897/BDJ.4.e8184

The owls beyond the Andes: Divergence between distant populations suggests new species

They might be looking quite identical, while perched above humanised farmlands and grasslands across several continents, but each of the populations of two owl species, living in the opposite hemispheres, might actually turn out to be yet another kind. This suggestion has been made by Dr. Nelson Colihueque and his team from Universidad de Los Lagos, Chile, based on new genetic divergence analyses of the Common Barn and the Short-eared Owl populations from southern Chile and comparing them with those from other geographic areas. The study is published in the open-access journal ZooKeys.

Although much has been known about the two widespread owl species, the knowledge about them has so far been restricted mainly to aspects such as their diet, conservation status and habitats. On the other hand, their genetic divergence in comparison with populations in distant areas has received little attention. Moreover, their taxonomical status is still based on traditional identification rather than modern methods such as the herein utilised mitochondrial COI sequencing.

Thus, the Chilean research team concluded a significant genetic divergence among the populations of both species from a few distinctive groups. In the case of the Common Barn Owl they compared the new analysis of its South American representatives with already available such data about populations from North America, Northern Europe and Australasia. For the Short-eared Owl, they compared Chilean and Argentinean birds with North American and North Asian.

One of the reasons behind such an evolutionary divergence might be the geographic isolation, experienced by the peripheral South American populations of both owl species. It is a consequence of the Andean Mountains acting as a natural barrier.

“In the case of the Common Barn Owl, the existence of geographic barriers to gene flow among populations on different continents is to be expected, and this in combination with its non-migratory or short-distance migratory behaviour, should contribute to promote the genetic divergence,” further explain the authors.

In conclusion, the researchers call for additional studies to clarify the taxonomic identification of these owl populations.

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Original source:

Colihueque N, Gantz A, Rau JR, Parraguez M (2015) Genetic divergence analysis of the Common Barn Owl Tyto alba (Scopoli, 1769) and the Short-eared Owl Asio flammeus (Pontoppidan, 1763) from southern Chile using COI sequence. ZooKeys 534: 135-146. doi: 10.3897/zookeys.534.5953