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Even within a single species, there can be great variations of plumage, size and behaviors. For example, I absolutely love red tailed hawks, their diversity is incredible. They also are a good example for this episode. At the very basic the red-tailed hawk is classified as a species with a species name of Buteo jamaicensis. From there they can be broken down into subspecies, of which there are 14. In addition, the red-tailed hawk has three color morphs, dark, light and rufous. But what is the difference in all these terms? What classifies a species, or a subspecies? All terms you would see very often in regards when someone is describing a bird. To understand these terms better and really appreciate bird diversity, we’re going to dip into taxonomy, which is the science of classifying organisms.
Current taxonomy has organisms broken down from largest groups to smallest, from genus, down to genera, families, then species. A species is defined as a unit of classification of an organism. At its simplest, it is defined as the largest group of organisms where two individuals can produce fertile offspring. Biologists then have to give each species a scientific name or a binomial nomenclature, which is a two part Latin name, the first part of the name is the genus in which the species belongs to. The second is the specific name, many times describing a major feature of the bird or sometimes named after the ornithologist that first discovered the bird species.
But while that definition of a species may seem simple enough, it’s not cut and dry, and classification can be complicated and many times not agreed on by all biologists. In addition, there are even species that can produce fertile hybrids, thus not really aligning with that description of what a species is. One such example that breaks that definition is the blue-winged warbler and the golden-winged warbler, species who can create hybrids that can also reproduce. These two species will routinely interbreed and create hybrids, the Brewster’s warbler and the Lawrence’s warbler. These hybrids will not only breed and reproduce with other hybrids, but also the two parent species, creating a range in possible appearance but also song style. This happens so routinely now that when you hear the song of either the blue-winged or golden-winged warbler, that you try and visually confirm if it really is the species you hear or if it is one of the hybrids. There is even an article published in 2006 that lists out 26 unique ways to define what makes a species, each has reasons for and against each method.
Boundaries between species are not always clear and exact. For example, species are constantly being reviewed, and depending on factors such as DNA, song and call dialects, plumage or behavior, may be lumped together, or split into multiple species. DNA analysis seems the most surefire way to classify a species but genetic studies are expensive and not feasible to test and organise all species. Then, with what amount of variation in their DNA would an individual be classified as a separate species? On top of that, evolution needs to be taken into consideration. It’s constantly happening, variations occur, and the same species in different areas may start to develop different traits. Over time they may become different species, it’s not always clear when and at what point that change in classification should occur.
Species are constantly being analyzed and sometimes can gain or lose the distinction of that label. Originally, the Baltimore Oriole and Bullock’s oriole were separate species, until a scientist decided they were actually just one species, the Northern oriole. Then in 1995, it was decided again that they were separate species. Other species that have been lumped together are the Yellow-shafted flicker and the Red-shafted flicker, which are now one species, the Northern Flicker that has two color forms. Just like some species are lumped together, others are split. For example the cackling goose used to be just considered a subspecies of the canada goose, now it’s recognised as its own species. These lumping and splitting of species is a good example of how organisms are constantly being reviewed to determine if they qualify to be their own unique species.
Since it is not always clear about how to classify an organism as a species, how do scientists and biologists go about determining what a species is? There are many ways that biologists can attempt to define and classify a species, whether that be morphology, their characteristics, or through genetics.
Originally, taxonomists, biologists who group organisms into categories, used morphology for species classification. Meaning that they categories species by their size, shape, structure and their characteristics. If they looked and acted the same, they must be the same species, if they were different, then they were a seperate species.
General characteristics such as plumage color, body shape and size, bill shape are important for a biologist to note when trying to classify a species. After that, more specific characteristics are also documented such as wing bars, facial markings, feather patterns and tail shape for example. All these major and minor characteristics are taken into consideration and compared with similar organisms to determine if it is unique enough to be classified as its own species.
Some species are so similar that one of the only reliable ways to tell the difference between them are their songs. Several flycatcher species in the genus Empidonax are an excellent example of this, even in the hand, there really isn’t any easy way to determine what species they are. Their calls and songs though are very different. Also, the eastern and western meadowlark look nearly identical, but due to having different songs, even in areas where their range overlaps, they do not interbreed, leading to them being classified as separate species.
Lately, Dna analysis has been used more often to try and classify species, where they will use phylogenetics to help make that determination. Phylogenetics is the study of how evolutionally related select organisms are to each other. While using this to help study and determine a species, it is also being used to determine a species ancestry and categorizing them by family. Which has led to many species family groups being completely changed over the years and scientists learning that birds that they previously believed were closely related were not, but more related to a different completely separate group of species than originally thought.
You may have noticed that not all birds of a specific species look alike. One individual from one part of the country may look or even behave differently from an individual on the other side of the country. Changes can occur to groups of a species that are separated geographically, often developing different characteristics such as plumage, diet, song and prefered habitat. These changes can lead to the need of a subcategory of a species.
So after you know what a species is, the next step down in classification can be a subspecies. Like the name implies, they are a subgroup of species that may have different characteristics. The most widely accepted definition for subspecies is from Mayr and Ashlock “A subspecies is an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species.” Which more simply is that a subspecies is a smaller subgroup of a species that is divided by range and displays slight variations in each of those ranges. A subspecies will also be given a third word to its scientific name, called a trinomen. For example the eastern red-tailed hawk subspecies will have the scientific name of Buteo jamaicensis borealis. For a species to have subspecies, it must have two or more subgroups, which can vary from the two like yellow-rumped warbler up to species like the song sparrow that has 24 different subspecies. Another term you may hear when someone is describing a species is being called a race or a form, these are usually used as a less formal term used in place of the word subspecies.