Why do some Brown Pelicans have orange or reddish parts on their bills?

Question

I am doing research on Brown Pelicans and have photos/descriptions of the breeding and nonbreeding appearances of adults, esp. the California and eastern subspecies here on our southern Pacific, Gulf of Mexico, and southern Atlantic coasts.

One question is really puzzling me:

The birds are described as having long pale bills, some with some brown on them. The bill of the California subspecies is described as acquiring some orange or red during the breeding season (along with the gular pouch which turns bright red/orange/pink). But I see photos of nonbreeding birds (with completely white necks) with either a little or quite a bit of orange on their bills, usually on the lower half.

There are so many pictures like this that the orange cannot be just a breeding color.

Do some Brown Pelicans just have some or quite a bit of orange on their bills, even when they are not breeding? I have looked at just about every link that comes up under Brown Pelicans and no one explains the presence of orange in some of their bills (except during the California subspecies' breeding season). In the official descriptions of the appearances of nonbreeding adults, orange in the bill is never mentioned. I would like to know the answer to this detail in the appearance of some of them!

Answer 1

After doing some reading at the Birds of North America webpage on Brown Pelicans.

It does mention orange on the bill outside of the breeding season. Brown Pelicans have a greenish gray bill once they are older than 24 days which becomes gray-brown in their first year. At around 12 to 14 months of age, yellow will begin to appear at tip and on the sides. At 16 to 19 months of age, the bill becomes gray-green-yellow with some orange, the orange becomes more distinct at 29 to 37 months.

It is difficult to define the plumage of a Brown Pelican during their first 2 to 3 years; they acquire definitive plumage between the ages of 3 to 5 years old.

Here are the descriptions of their bill in Definitive Basic and Alternate plumages:

In Definitive Basic plumage, proximal end of upper mandible pinkish orange, distal end buff yellow over pinkish orange, and nail at tip buff yellow. Lower mandible pinkish orange, except middle section gray or mottled gray. Proximal end of gular pouch reddish orange (P. o. californicus) or green-gray (P. o. carolinensis); distal end dark gray-green. As breeding season approaches, colors intensify; bill becomes brightest 4–6 weeks before pouch.

In Definitive Alternate plumage, upper mandible bluish pearl-gray and pinkish on proximal end, buff-yellow-orange-red over bluish pearl-gray on distal end, and bright buff-yellow on nail. Lower mandible pale yellow on proximal third, bluish pearl-gray elsewhere; yellow at maximum intensity when young being fed; may serve as target for begging nestlings.

Colors fade with onset of incubation through prebasic molt; upper mandible gray proximally, buff-yellow and orange over pearl-gray distally, and buff-yellow on nail; distal two-thirds of lower mandible gray; proximal end of gular pouch faded yellow-gray (P. o. californicus) or gray-green (P. o. carolinensis); distal end dark green.

It appears their bill does retain the orange after breeding although it may begin to fade and it does mention how the colour intensifies during breeding.

Reference:

Shields, Mark.(2014).Brown Pelican (Pelecanus occidentalis), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/brnpel

Answer 2

It reminds me of the red spot on the seagulls bills of the classic study by Niko Tinbergen.

In the mid-20th Century, Dutch scientist Niko Tinbergen studied nesting Herring Gulls. He noticed that newly hatched gull chicks were fed by their parents only after they pecked at the adults' bills. Tinbergen devised experiments that varied the shape and coloration of the adult's bill. It became clear that the red spot on the adult gull's bill was a crucial visual cue in a chick's demands to be fed, and thus its survival.

It may be that the same mechanism is used by the brown pelican to elicit a stimulation from the chick.