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Franklin's Gull • Leucophaeus pipixcan

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A Franklins Gull for Bird Count 29. I see thousands of them every time i go out birding its almost unreal how many there are.

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Juveniles

August 22, 2024

Juvenile California Gull

Now that most of the local Olympic Gulls are out of their nests, scattered along beaches, docks and alleyways, I think it would be a good time to talk about juvenile plumages. I would also like to briefly explore the types of moult that young birds undergo in early life, particularly in their first year.

Juvenile Plumage

Nestlings in most species begin replacing their natal down in the nest in a process called prejuvenile moult, which results in juvenile plumage.* Juvenile plumages (and subsequent immature plumages, like those of larger land birds and gulls) are fascinating, fine-tuned to give a young bird the best chance of survival. Thrushes like American Robins are speckled with dots and teardrop patterns to confuse a chasing predator, while the muted grey and brown colourations of Larus gulls act as camouflage. In fact, as for adult birds, juvenile plumages serve multiple and often conflicting functions (e.g. predator confusion vs camouflage), which find balance through natural and sexual selection.1

Fledgling Swainson's Thrush. Notice the buff teardrops on the upperparts and speckled chest.

Formative Plumage

There is also a wide variety of moult strategies for immature birds. In most cases, juvenile feathers have to grow quickly, being semi-functional by the time the bird has left the nest. Because of this, these feathers are of lower quality than adult feathers. Combined that with the fact that most species have a longer delay between prejuvenile (first prebasic) and second prebasic moult than subsequent moults, many species have supplemental moults to maintain feather quality.2 The preformative moult takes place after, or even before, the prejuvenile moult has completed, producing formative plumage. In many songbirds, and small gulls like Bonaparte's and Franklin's Gull, this moult is limited to body feathers and some coverts, though there is much variation.

First cycle Franklin's Gull. This individual has some grey feathers appearing on its upperparts, marking the start of the preformative moult.

Alternate Plumage

Larger gulls (Glaucous-winged Gull, Herring Gull, Ring-billed Gull, etc.) do not have a preformative moult.** Whereas the prebasic moult is usually complete (replacing body and flight feathers) and coincides with the nonbreeding season, the prealternate moult replaces less feathers. Alternate plumage--think of it as alternating with basic plumage annually--is completed around the breeding season for many species, and is often when you see birds at their most colourful. Birds that take multiple years to reach adulthood still undergo this prealternate "prebreeding" moult--it just looks a little messy. When my local Olympic Gull Juveniles start developing grey feathers on their backs, that is the prealternate moult in progress.

First cycle Ring-billed Gull beginning its prealternate moult (light grey on upperparts).

I know I am throwing a lot of jargon around--moults, cycles and bears, oh my! If anything, this is just me, a novice birder, trying to express my excitement about such misunderstood and under appreciated subjects as the plumages of juvenile and immature birds and the process of moult in general.

Until next time.

*I might confuse a few people writing about H-P terminology and the WRP system in Canadian English. Hopefully more Old World articles begin to be written using these standards, trading in Life Cycle terminology, which has an initially shallow learning curve, with that which better accounts for eclipse plumages in ducks and variation in moult duration in neotropical birds.3

**Preformative moults actually occur in most birds, according to Pyle. However, it is not appreciable enough in the larus gulls I come across. I need to look into this further.

References

Jenni, Lukas, and Raffael Winkler. “The Biology of Moult in Birds.” Bloomsbury Publishing, 2020, pp. 10.

Pyle, Peter. “Identification Guide to North American Birds.” Part 1, Second Edition, Slate Creek Press, California, 2022, pp 16.

Wolfe, Jared D, et al. “Ecological and evolutionary significance of molt in lowland Neotropical landbirds.” Ornithology, Volume 138, Issue 1, 2021. doi.org/10.1093/ornithology/ukaa073

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Franklin’s Gull in the Birbs of Saskatchetoon Sketchbook

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