Larus cachinnans in the Netherlands

(last update: February 17, 2023)

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Cachinnans - nest Lelystad y-XCHP

Originally, this nest at dam 2 at colony Lelystad was marked "221" in April 2022, but was soon renamed y[XCHP] once we observed the ringed bird at this location. Many images, throughout the next months, proof the birds in the pictures are indeed the parents for chicks r-5.0 and chick r-5.1.

Images below show both chicks, which appear very cachinnans-like and in fact hardly show clues indicating these are offspring of hybrid parents.
In fresh juvenile plumage, cachinnans appear overall brown and steaked, which may come as a surprise, but remember this is how fresh juveniles of many gull species appear in June. In June, the pattern is more important that the coloration, and both birds show dark outerwebs on the inner primaries, and vermiculated basal rectrices, typical for cachinnans. Slightly odd features for cachinnans, and probably more in line with some argentatus influences are the barred brown underwing (not as pale as in some pure cachinnans), and the anchor pattern on tertial tips.

After the partial autumn moult, both birds developed into quite classic 1st winter cachinnans, with pale head, a collar of streaking concentrated in the hindneck, grey based scapulars with thin anchor patterns, and dark centred tertials.
In r-5.0 the wing-covert panel remained juvenile, but r-5.1 moulted several coverts to 2nd generation. Adding to the cachinnans-look are the slender parallel bill, long and pale legs, and sloped forehead.
If these birds were not ringed, they would probably be dismissed as pure cachinnans?

5.0 ringed as chick on May 30th, 2022. Page on gull-research.org for r-5.0 (with photo credits).	5.0 on June 28th, 2022. Both juveniles 5.0 & 5.1 taking off and showing cachinnans-like primary patterns, with largely dark outerwebs.	5.0 on June 28th, 2022. Brown plumage may come as a surprise, and probably not associated with cachinnans by some observers, but in fact this is the norm for many pure birds.	5.0 on December 3rd, 2022 in n. Spain. Migrated to Iberia. White-headed, with streaked collar in hindneck, solid tertials, pencil-shaped bill, and 2nd generation scapulars with thin anchor-patterns on greyish base all nicely match pure cachinnans.
5.1 ringed as chick on May 30th, 2022. Page on gull-research.org for r-5.1 (with photo credits).	5.1 on August 7th, 2022. Plumage patterns and jizz already very cachinnans-like.	5.1 on September 26th, 2022. Starts to develop characteristic pale underparts and head. Note exposed long-looking tibia.	5.1 on February 15th, 2023. Replaced wing-coverts and collar of streaks in hindneck add to cachinnans-looks. If no parential history was known from the ring, probably this bird would be ID-ed as pure cachinnans?

Images below: both parents clearly have cachinnans characteristics, but also show single traits indicating a probable hybrid origin.

XCHP 1CY, December 11th, 2018. In all aspects a classic 1st winter cachinnans. Page on gull-research.org for y-XCHP.	XCHP 5CY, April 11th, 2022. Complete solid sub-terminal band on P10, and, more important, P9 completely lacks a mirror. No mirror on P9 is rare in pure cachinnans of 5 years and older.	XCHP 5CY, June 21st, 2022. Head with rather short and high bill. Orbital ring red.	XCHP 5CY, November 7th, 2022. Iris turning paler, and note again rather short and high bill.
4CY cachinnans type, April 12th, 2022. Both parents near the nest.	4CY cachinnans type, April 12th, 2022. Wingtip pattern may still change with age.	4CY cachinnans type, April 12th, 2022. Like it's partner, with rather stubby and high bill.	4CY cachinnans type, May 4th, 2022.

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General remarks:

• Eggs: Volume measured by Stonehouse (1964) and Spaans & Spaans (1975), which make comparison possible with data from Texel (Camphuysen pers comm 16.04.2020).
• Nest 221 positioned at breakwater 2 - east, low between blocks. In April 2022, y-XCHP was suspected to breed at nest 55, but April 29th we concluded the nest was 10 meters to the south.
  In 2023 same birds at almost same location (just 3 meters more east).
• ID 2022 certain, sub-adult Caspian Gull cachinnans type and partner is hybrid 5CY y-XCHP from Germany (5CY without mirror on P9 and full band on P10, still some cachinnans traits visible).
• ID 2023 certain, adult Caspian Gull cachinnans and 6CY y-XCHP.
• ID 2024 certain, adult male Caspian Gull cachinnans and 7CY female y-XCHP. Certainly same birds.

location	April 29th, 2022: nest location.	April 29th, 2022: 2 eggs clutch.	April 29th, 2022: 2 parents.
location	April 23rd, 2024: both parents present.	April 23rd, 2024: both parents present.	April 30th, 2024: both parents present.
	April 29th, 2022: 2 eggs clutch.	April 9th, 2023: 2 eggs clutch.	April 26th, 2023: 3 eggs clutch.
partner 1	April 11th, 2022: cachinnans hybrid 5CY y-XCHP.	April 11th, 2022: cachinnans hybrid 5CY y-XCHP.	April 11th, 2022: cachinnans hybrid 5CY y-XCHP.
.	May 13th, 2023: cachinnans hybrid 6CY y-XCHP.	March 25th, 2024: cachinnans hybrid 7CY y-XCHP.	March 25th, 2024: cachinnans hybrid 7CY y-XCHP.
.	April 23rd, 2024: cachinnans hybrid 7CY y-XCHP.	April 23rd, 2024: cachinnans hybrid 7CY y-XCHP.	April 23rd, 2024: cachinnans hybrid 7CY y-XCHP.
partner 2	April 12th, 2022: male cachinnans type 4CY.	April 12th, 2022: cachinnans type 4CY.	April 12th, 2022: cachinnans type 4CY.
	June 25th, 2023: male partner is now 5CY.	April 23rd, 2024: male partner is now 6CY.	April 23rd, 2024: male partner is now 6CY.
partner 2	April 23rd, 2024: male partner is now 6CY.	April 23rd, 2024: male partner is now 6CY.	.
pullus	June 21st, 2022: chick r-5.0.	August 7th, 2022: r-5.1 at Almere.	May 11th, 2023: ringed chick r-8.S.
pullus	July 8th, 2023: fledged chick r-8.9.	May 14 2024: pullus g-B|S.	June 18 2024: pullus g-B|T.
food	May 14 2024: worms.	May 14 2024: Goby species.	.

Visits and data 2022.

Visits and data 2024.