The Eastern Meadowlark (Sturnella magna) and Western Meadowlark (Sturnella neglecta) are two closely related birds found across North America. Despite their similarities in appearance and behavior, they are considered separate species by ornithologists due to several key differences. In this article, we will explore the distinguishing features that set these meadowlarks apart, including their songs, geographic ranges, morphology, and genetics. Understanding what defines a species and the specific criteria used to delimit the Eastern and Western Meadowlarks provides insight into the fascinating diversity of life.
Geographic Ranges
The most obvious difference between the Eastern and Western Meadowlarks is their geographic distribution across North America. As their names suggest, Eastern Meadowlarks are found mainly in the eastern half of the continent, while Western Meadowlarks primarily occupy the western half:
Eastern Meadowlark range
- Breed from southern Ontario east to Nova Scotia and south to Florida and eastern Texas
- Winters in southeastern U.S. from North Carolina south to Florida and west to central Texas
- Migrates through the Great Plains states between breeding and wintering grounds
Western Meadowlark range
- Breeds from central British Columbia east to south-central Manitoba and south throughout the western half of U.S. to northern Mexico
- Winters in southwestern U.S. south to central Mexico
- Year-round resident in much of range away from northernmost breeding areas
The birds co-occur across a narrow zone from central Kansas through Nebraska, South Dakota, and Minnesota. However, even within this transition zone, the two meadowlarks partition themselves into different breeding habitats, with Westerns in drier, shortgrass prairie and Easterns in wetter, tallgrass areas. This geographic isolation and lack of interbreeding initially led scientists to classify them as separate species.
Song Differences
In addition to their distinct ranges, Eastern and Western Meadowlarks exhibit clear differences in their songs and vocalizations. Song plays an important role in mate attraction and breeding territory defense for these birds. The most conspicuous parts of their songs, the flute-like whistle sections, sound quite different:
Eastern Meadowlark song
- Clear, loud, slurred whistles
- Whistles often described as “spring-of-the-year” or “see-you”
- Whistles usually comprised of 2-6 notes)
- Average song length is about 3 seconds
Western Meadowlark song
- Buzzier, more clipped whistles
- Whistles often rendered as “pizz-urrr” or “kee-arr”
- Whistles typically only 2-3 notes
- Average song length is about 2 seconds
These whistle differences are consistent across their respective ranges. The songs are distinctive enough that observers can often identify the species without seeing the birds. The divergent songs likely play an important role as a reproductive isolating mechanism between the Eastern and Western Meadowlarks.
Morphological Differences
Eastern and Western Meadowlarks are also distinguished by subtle differences in their physical appearance and morphology:
Eastern Meadowlark
- Slightly smaller in body mass on average
- Shorter wings
- Longer tail
- Brighter yellow breast with black “V”
- White outer tail feathers
Western Meadowlark
- Slightly heftier build
- Longer wings
- Shorter tail
- Duller yellow underparts with darker mottling
- No white in tail
These physical differences represent subtle adaptations to the habitats where the two meadowlarks breed. For example, Eastern Meadowlarks require more maneuverability and a longer tail to avoid obstacles in dense, grassy habitat. Western Meadowlarks have slightly longer wings for sustained flight over open plains. While their appearances overlap broadly, the consistent morphological differences help strengthen the case for treating them as separate species.
Genetic Evidence
The geographic, vocal, and morphological distinctions between Eastern and Western Meadowlarks provide convincing evidence they are distinct. Analyses of the birds’ genetics deliver further validation. For example, studies of mitochondrial DNA, inherited only from the mother, reveal sequence differences between Eastern and Western Meadowlark populations. Examining nuclear DNA also uncovered genetic divergence between the two meadowlarks consistent with their status as separate species.
In one comprehensive study looking at genetic variation, researchers found Eastern and Western Meadowlarks grouped into two distinct clusters with minimal overlap. Within the transition zone where their ranges meet, individuals showed mixed genetic signals but could still be assigned reliably to either the Eastern or Western species based on specific allele differences. This zone of intergradation likely represents a mixing of the two genomes after previous isolation, rather than ongoing gene flow between the species. The collective genetic data provide powerful confirmation that these bird populations have evolved separately for a considerable time.
Hybridization
Researchers have documented a narrow hybrid zone between the two meadowlarks where their ranges come together in the Great Plains. Hybridization events represent important opportunities to study the dynamics of speciation and maintenance of species boundaries.
Several findings from examining Eastern-Western Meadowlark hybrids:
- Hybrids occur at low frequencies, less than 5% within the hybrid zone
- Hybrids form when an Eastern or Western mates with the opposite species, not through hybrids interbreeding
- Male hybrids exhibit intermediate song features, suggesting learned vocalizations help isolate Eastern and Western Meadowlarks reproductively
- The species’ distinct genetic and phenotypic profiles remain despite some interbreeding, highlighting differentiation built up during past isolation
This limited hybridization helps explain the patchy distribution of characters and blurry species boundary observed where the two meadowlarks meet. However, it does not contradict their identity as biologically distinct species that remain predominantly separate.
Recognition as Separate Species
Ornithologists historically lumped the Eastern and Western Meadowlarks into a single widespread species. In the early 1900s, scientists started describing key differences between the birds and splitting them based on geography. By the 1930s, most taxonomists recognized them as distinct species based on their songs, morphology, and non-overlapping ranges. This treatment of the Eastern and Western Meadowlark as separate species has remained stable in the scientific literature for nearly a century since.
Recent advances, such as genetic analysis and playback experiments, have only bolstered the case that these birds deserve species status. Contemporary taxonomic authorities, including the American Ornithological Society and the International Ornithologists’ Union, affirm the Eastern and Western Meadowlarks as distinct. The consensus relies on evidence of reproductive isolation and evolutionary divergence meeting the criteria for the Biological Species Concept. In summary, the totality of differences across multiple features demonstrate these meadowlarks represent two unique, cohesive species.
Conclusion
While superficially similar, the Eastern and Western Meadowlarks exhibit consistent differences in their songs, geographic distribution, morphology, and genetics. These distinguishing characteristics reflect evolutionary divergence molded by past isolation and natural selection pressures unique to each population. Limited interbreeding occurs where the birds’ ranges now connect, but this has not prevented them from maintaining their integrity as distinct species over time. Ornithologists’ recognition of the Eastern and Western Meadowlarks as separate reflects a wealth of evidence demonstrating these songbirds are distinct biological entities that have charted their own evolutionary courses. Appreciating subtle differences hidden within the birds we see is one of the great joys of biology and continues to reveal new insights into life’s multitude of forms.