Starlings and grackles are two types of songbirds that are commonly seen across North America. At first glance, they may appear quite similar – both are black, glossy birds that often flock together. This can lead some to wonder, are starlings and grackles actually related? Or are they completely separate species that have evolved similar adaptations?
Quick Overview: Starlings vs Grackles
Let’s start with a quick overview of some key facts about starlings and grackles:
Starlings
– Species name: European Starling (Sturnus vulgaris)
– Size: About 8-9 inches long
– Identifying features: Short tail, triangular wings, sharp slender beak. Adults are glossy black with small white spots in winter.
– Habitat: Variety of open and semi-open habitats from grasslands to cities. Often found in large flocks.
– Origin: Native to Europe, Asia and North Africa. Introduced to North America in 1890s.
Grackles
– Species names: Common Grackle (Quiscalus quiscula), Boat-tailed Grackle (Quiscalus major), Great-tailed Grackle (Quiscalus mexicanus)
– Size: 11-13 inches long
– Identifying features: Long crow-like beak, long keel-shaped tail. Males are iridescent black, females are brown.
– Habitat: Open woodlands, forests, grasslands, marshes, parks, farms. Form large nesting colonies.
– Origin: Native to North and South America.
So while starlings and grackles overlap in some ways, they are clearly different species based on their origins, anatomy, and scientific classification. But why is this? What evolutionary histories led to the similarities and differences between the two groups?
Taxonomy and Evolutionary History
To really determine if starlings and grackles are closely related, we need to look at how they are classified taxonomically and what the evolutionary history tells us.
Starlings belong to the family Sturnidae and are placed in the songbird order Passeriformes. The Sturnidae family contains around 120 species of starlings found throughout Europe, Asia and Africa. This includes birds like mynas, oxpeckers and mockigbirds.
Grackles, on the other hand, belong to the Icteridae family within the Passeriformes order. The Icteridae family consists of blackbirds, orioles, cowbirds and others, all exclusively found in the Americas.
So taxonomically, starlings and grackles belong to different bird families that are not closely related within the Passeriformes order. In fact, passerines are an enormously diverse order containing over 5,000 species. There are dozens of families within this order that have all evolved quite distinctly.
Looking back millions of years, starlings and grackles evolved on completely different continents separated by oceans. The Sturnidae family containing starlings originated in the Old World, likely Southeast Asia. They later diversified and spread to populate Europe, Asia and Africa.
Meanwhile, grackles come from a family that evolved entirely in the New World. The Icteridae originated in South America and later members like grackles adapted to habitats in North America.
So in evolutionary history, starlings and grackles came from ancestral songbird lineages that adapted and diversified on separate continents long ago. This deep division between Old World and New World songbird families is why starlings and grackles are not actually close relatives at all.
Convergent Evolution
If starlings and grackles are not closely related, how do we explain their similarities in appearance and behavior? This comes down to the phenomenon of convergent evolution.
Convergent evolution is when unrelated species adapt similar traits independently. It often occurs when animals come to occupy similar ecological niches or habitats. In these situations, natural selection pressure can drive multiple species to evolve analogous physical and behavioral adaptations – even if they are not closely related.
Starlings and grackles provide a good example of convergent evolution. Though they came from distant ancestors, they have both adapted to live in open habitats like grasslands, farms, and urban areas. Frequenting similar environments seems to have led both species to evolve:
– Black plumage that is iridescent. This likely helps with camouflage, mimicry, and mate signaling.
– Long slender beaks suited for an omnivorous diet – eating both insects and fruits/seeds.
– Gregarious flocking behavior and noisy vocalizations to stay in contact and find food.
– Ability to thrive in human-disturbed areas. They nest on buildings and scavenge waste in urban environments.
Since starlings and grackles faced comparable natural selection pressures, they independently evolved analogous physical and behavioral traits that are well-suited to their way of life. This convergent evolution makes them appear more similar than their actual evolutionary relationship would suggest.
Differences Between Starlings and Grackles
Despite some superficial similarities, starlings and grackles still have clear anatomical and life history differences due to their distant evolutionary lineages. Some key differences include:
Anatomy
– Size: Grackles are significantly larger. The common grackle is about 25% longer than the European starling.
– Shape: Starlings have proportionally shorter and triangular-shaped wings and tails compared to grackles.
– Bill shape: Starlings have a slender, pointed bill while grackles have a longer, broader bill that is more crow-like.
– Plumage: While both have iridescent black feathers, starling plumage has a more greenish-purplish sheen while grackles show more bronzy-yellow iridescence.
– Sexual dimorphism: Male and female grackles can be distinguished by plumage color. Starlings are identical.
Behavior and Habitat
– Flocking: Starlings form immense winter flocks of hundreds of thousands. Grackle flocks are smaller, usually under 1,000 birds.
– Migration: Some grackle populations are long distance migrants, traveling from as far north as Canada to South America. Starlings are predominantly short distance migrants.
– Breeding: Grackles nest in colonies, often in wetland vegetation. Starlings nest in cavities, manmade structures, or crevices.
– Diet: Starlings eat more terrestrial insects like beetles. Grackles consume more aquatic prey like crustaceans and fish.
– Habitat: Grackles are more associated with wetland habitats compared to starlings. However, both occupy urban and agricultural areas.
So while starlings and grackles share some general traits, a closer look makes it clear they have many distinct characteristics attributable to their unrelated evolutionary histories and adaptations.
Conclusion
In summary, starlings and grackles are not actually close relatives despite some similarities in appearance and behavior. Taxonomically they belong to different families – Sturnidae and Icteridae. These families have very distant evolutionary origins on separate continents. Their analogous features like black plumage, gregariousness and omnivorous diet are the product of convergent evolution, not close ancestry. A deeper comparison also reveals key physical and life history differences between the two groups. So starlings and grackles provide a good example of how unrelated species can evolve similar traits when they adapt to comparable environments and ecological roles. Their relationship reflects convergent evolution rather than close kinship.