Gulls and terns are two types of seabirds that are often confused with one another. At a glance, they appear quite similar – they are both medium to large-sized birds with long wings and short legs. However, there are several key differences between gulls and terns that set them apart.
Quick Answers
Gulls and terns belong to different bird families – gulls are in the family Laridae, while terns belong to Sternidae.
Gulls tend to be more robustly built, with stouter bills and thicker necks compared to the slender build of terns.
Terns are lighter and more graceful in flight compared to gulls.
Gulls have webbed feet, while terns have slender bills with sharp points.
Most gull species are omnivores, while terns feed primarily on fish.
Gulls are found across a wide range of habitats, but terns are restricted to coastal regions.
Gulls are usually gray and white in color, while terns have black caps and white bodies.
Taxonomy and Evolution
Gulls and terns belong to two separate families in the order Charadriiformes, which includes shorebirds, gulls, terns, skimmers, and auks. The family Laridae includes the gulls and their close relatives the skimmers, while the terns belong to the family Sternidae.
Gulls are thought to have evolved around 25 million years ago during the Miocene epoch, diverging from a common ancestor shared with waders like plovers. Terns evolved more recently, diverging from the gulls around 15 million years ago during the Miocene. Thus, while gulls and terns occupy similar coastal niches today, they descended from different ancestral lineages.
Key Evolutionary Differences
Gulls evolved stouter bills and heavier bodies compared to their ancestors, allowing them to tackle a wide range of food sources both along the coast and further inland. In contrast, terns maintained a lighter build with slender, pointed bills adapted for catching fish on the wing.
Gulls also developed webbed feet for swimming and walking over various surfaces, while terns retained lighter feet for optimal flight maneuverability.
Differences in migratory patterns also emerged – most gulls tend to be partially migratory or not migrate at all, while many terns embark on long transoceanic migrations.
Physical Differences
While gulls and terns fill similar ecological roles along the coast and at sea, there are several key physical differences between them:
Size and Build
Gulls tend to have a bulkier, more robust body plan compared to terns. Even gull species of a similar weight have a thicker neck, broader chest, and blunter wings than terns. Terns have exceptionally long, slender wings and narrow, streamlined bodies adapted for agile flight and diving for fish.
Bills
Gulls have heavy, stout bills that are slightly hooked at the end – ideal for a varied diet including fish, invertebrates, eggs, small animals, and carrion. A gull’s bill can exert a lot of force for prying open shellfish, tearing flesh, and cracking hard food items.
In contrast, terns have slender, pointed bills adapted for spearing and grasping slippery fish. A tern’s bill has very little crushing power but is designed for piercing prey and holding onto it in flight.
Feet
Gulls have fully webbed feet with noticeable flaps of skin between their front three toes. Webbed feet provide an advantage when swimming, walking on various surfaces, and shuffling along the ground to make nests.
Terns have lighter, less-webbed feet with slimmer toes. Their feet are optimized for perching on posts and buoys and provide less resistance in water when plunge diving.
Trait | Gulls | Terns |
---|---|---|
Size | Bulkier, more robust | Slender, streamlined |
Bill Shape | Thick, blunt, hooked | Slim, pointed |
Feet | Fully webbed | Partially webbed |
Plumage Differences
Gulls and terns also differ noticeably when it comes to their plumage:
Color Patterns
Gulls tend to have simple patterns of gray and white. Depending on the species, their heads can be white or gray, and they may have black wingtips or spots on their wing feathers. In winter, the head often becomes streaked with brown.
In contrast, terns have black caps on their heads that contrast sharply with their white foreheads and bodies. Their black caps are maintained year-round. The wing and back feathers of terns are a light gray, and their bills are orange-red or black.
Juvenile Plumage
Juvenile gulls have drab brown plumage that gradually lightens to adult colors over several years. This helps camouflage young gulls.
Young terns, on the other hand, are gray-brown overall but still retain the black cap of adult terns soon after hatching. This may help with visual recognition and feeding by the parents.
Plumage | Gulls | Terns |
---|---|---|
Adult colors | Gray and white | Black cap, white body |
Juvenile plumage | Drab brown | Gray-brown with black cap |
Ecological Differences
While their ranges overlap along coasts worldwide, gulls and terns differ significantly when it comes to their ecology:
Habitats
Gulls utilize a wide array of habitats, both along the coast and further inland. They are fixture in harbors, beaches, rocky cliffs, grasslands, cities, and even arctic and desert environments.
In comparison, terns are specialized for life along the coast and are rarely found far inland. They require beaches or islands close to productive fishing grounds.
Migration
Most gull species are partially migratory or resident year-round in their breeding range. Some high-latitude gulls migrate south in the winter, but many remain along coasts year-round.
In contrast, the majority of terns are long-distance migrants that winter and breed in widely separated regions. They undertake transoceanic journeys each fall and spring between breeding and nonbreeding areas.
Diet
Gulls are omnivores and opportunistic feeders that consume a wide variety of prey including fish, marine invertebrates, eggs, young birds, small mammals, insects, carrion, scraps, and garbage.
Terns are specialized for feeding on fish and occasionally small squid. A tern’s diet consists almost entirely of small marine forage fish like herring, anchovies, and sardines.
Ecology | Gulls | Terns |
---|---|---|
Habitats | Wide range | Mainly coasts |
Migration | Partial or none | Long-distance |
Diet | Omnivorous | Fish-specialist |
Behavioral Differences
Gulls and terns also differ in many aspects of their behavior:
Flight Style
Gulls have a heavier flight pattern with slower, more deliberate wingbeats. Their flight appears lumbering at times. They use a mixture of gliding and flapping flight.
Terns are exceptionally graceful and agile in the air. They utilize long, elegant glides punctuated by rapid flurries of wingbeats. Their flight appears effortless and buoyant.
Diving
Gulls rarely plunge dive and instead pick prey from the surface or shallow water. The few species that do dive underwater don’t go deeper than several feet.
Terns routinely execute steep plunge dives from heights of 10-30 meters to catch fish. They hit the water at high speeds and go underwater to depths of 1-3 meters when hunting.
Social Behavior
Gulls are highly social and nest in dense colonies that can number in the thousands. They actively scrounge for food and engage in complex social interactions.
Most terns tend to be less social and aggressive. Some species nest in colonies while others are more solitary. Terns rely more on aerial hunting than direct competition for food.
Behavior | Gulls | Terns |
---|---|---|
Flight style | Heavier, flapping | Graceful, buoyant |
Diving habits | Surface-picking | Plunge diving |
Social habits | Highly social | Less social |
Conclusion
While gulls and terns fill similar niches as coastal and pelagic feeders, they belong to separate families that diverged millions of years ago and exhibit key differences in anatomy, ecology, and behavior.
Gulls tend to be bulkier and more omnivorous generalists, feeding on a wide array of prey in diverse habitats. Terns are specialized fish-eaters with more delicate builds optimized for plunge diving and flight maneuverability. Their distributions and migratory habits also differ, with terns focused on coasts and undertaking long transoceanic journeys.
So while gulls and terns appear similar from a distance, their evolutionary paths have shaped them into distinct types of seabirds with unique adaptations for life in their marine environments. Paying attention to differences in bill shape, feet, plumage, and flight style is the best way to distinguish between gulls and terns in the field.