Birds come in a stunning array of shapes, sizes, colors, and behaviors. With over 10,000 species of birds in the world, identifying a specific bird based on a single distinguishing feature can be a challenge. However, focusing on key characteristics like the plumage pattern under the wings can help narrow the possibilities.
Looking for White Spots Under the Wings
When it comes to a white spot under the wings, one bird family stands out – the gulls. Gulls are medium to large birds in the Laridae family, and many species have a distinctive white “mirror” marking under their wings when in flight. This white spot contrasts with the gray or black plumage on the rest of the wings, making it very noticeable.
The white wing mirror is caused by a patch of white feathers under the wings. When the gull is at rest, the wing mirrors may be hidden from view. But when the bird takes flight, the white feathers become visible underneath, like a flash of bright light. This makes the wing mirrors helpful for identifying gull species in mid-air.
Common Gulls with White Mirrors
Some of the most common gull species that display the white mirror pattern include:
- Herring Gull
- Ring-billed Gull
- California Gull
- Great Black-backed Gull
- Laughing Gull
- Franklin’s Gull
- Mew Gull
The white patch may vary in size between species and individual birds. For example, the Herring Gull has a very large white mirror that is obvious during flight. Franklin’s Gull has a smaller mirror, and the Ring-billed Gull’s mirror is semicircular shaped.
Purpose of the White Wing Spot
Researchers aren’t entirely sure about the function of the white wing spot on gulls. Some of the proposed explanations include:
- Visual signal – The bright white patch could allow gulls to identify and follow each other in flight. This would be helpful when flocking or migrating over long distances.
- Mate attraction – Similar to other white plumage patches, the wing mirrors may play a role in courtship and attracting mates.
- Distraction – The flashing white feathers could help distract or confuse potential predators that are attacking from below.
More research is needed to determine the advantages conferred by the wing mirrors and why this trait evolved in so many gull species.
How to Identify Gulls in Flight
Spotting a seabird overhead with a white flash under its wings is a good indication it’s likely a gull. But how can you identify which gull species?
Here are some tips for identifying gulls based on their white wing mirrors:
- Size – Larger gulls like the Herring Gull have very large wing mirrors, while smaller gulls have smaller patches.
- Shape – The shape can vary from circular to semicircular or triangular. The Ring-billed Gull has a very distinctive semicircular mirror.
- Location – The placement on the underside of the wing can help. For example, on the Laughing Gull it is more towards the wingtip.
- Plumage – Note the main plumage color on the rest of the wing and body. This can rule out lookalikes that don’t match the typical species plumage.
- Flight style – Gulls have buoyant, often erratic flight. Compare to similar seabirds like terns which have smoother gliding.
Taking note of all these features together can help pinpoint the exact species, even if you only get a brief overhead glimpse.
Other Key ID Tips for Gulls
The wing mirrors are extremely helpful for identifying gulls in flight. But there are some other key characteristics to note as well:
- Bill size and shape
- Head shape
- Leg and foot color
- Tail pattern
- Beak and eye color
For example, the Herring Gull has a heavy yellow bill, pink legs, and a red spot on its lower mandible. The California Gull has a smaller bill that is more slender and darker, with greenish-yellow legs. Head streaking patterns, eye color, and tail markings also differ between species.
Taking the time to observe gulls at rest on the ground or perched on water can allow you to discern these more subtle features. Combining these clues with the wing mirror signature makes gull identification much easier.
Similar Species to Rule Out
Sometimes other coastal birds can be mistaken for gulls at first glance. Here are a few similar species that lack the telltale white wing patch:
Terns
Terns belong to the same order as gulls but a different family (Laridae vs. Sternidae). They are graceful, streamlined birds with narrower wings and different flight patterns. Most terns do not have white underwing markings, so this is a key difference to note.
Skimmers
Skimmers like the Black Skimmer have unique bills with a lower mandible that is much longer than the upper. They also have different body proportions than gulls and white wing patches only on some species.
Jaegers
Jaegers are seabirds that pursue other birds to steal food in flight (kleptoparasitism). They have elongated central tail feathers and very long, pointed wings. When seen overhead, jaegers will not display white underwing patches.
Bird | Description | Distinguishing Features |
---|---|---|
Gulls | Medium to large seabirds with heavy straight bills, buouyant flight, and white wing mirrors | White patch under wings visible in flight |
Terns | Smaller seabirds with slender bills, smooth flight, and long tail streamers | No white wing patches |
Skimmers | Unusual beak has elongated lower mandible. Large white wing stripes on some. | Different bill shape, white patches only on some species |
Jaegers | Pursuit predators with sleek, agile flight. Elongated central tail feathers. | No white underwing markings |
Conclusion
The distinct white patch or “mirror” seen flashing under the wings of gulls in flight sets them apart from other seabirds. This useful identification clue separates gulls from related families like terns and skimmers that lack similar underwing markings. Paying attention to the size, shape, location, and plumage characteristics of this white spot can help determine the specific gull species. Using the wing mirrors along with other features like bill size and head pattern allows even seasoned birders to confidently identify gulls passing overhead.