Larus cachinnans in the Netherlands

(last update: August 16, 2020)
Coordinator:
Albert de Jong
Merijn Loeve
Roland-Jan Buijs
Thijs Horst
Leon Kelder
Mars Muusse

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Nests at De Kreupel 2020
nest r-02P4 20
nest y-X804 20
nest D01 20
nest D02 20
nest D03 20
nest L01 20
nest L02 20
nest L03 20
nest M02 20

Nests at De Kreupel 2021
nest r-02P4 20
nest w-201U 21
nest g-XLHD 21
nest r-KA 21
nest r-KB 21
nest r-KC 21
nest r-KD 21
nest r-KE 21
nest r-KF 21
nest r-KH 21
nest r-KJ 21
nest r-KK 21
nest A01 21
nest C03 21
nest C04 21
nest C06 21
nest D01 21
nest D03 21
nest D05 21
nest D06 21
nest D07 21
nest D08 21
nest E01 21
nest H01 21
nest L01 21
nest L02 21
nest L05 21
nest L06 21
nest L07 21
nest M01 21
nest M04 21
nest M06 21
nest Q01 21

Caspian Gull cachinnans hybrid FP 1CY-4CY, May 2021 - March 2024, De Kreupel & Medemblik, the Netherlands. Picture: Leon Kelder, Thijs Horst & Mars Muusse.

Pale blue tibia ring p[FP] and metal Arnhem 5.556.712, ringed as pullus Larus cachinnans-type on May 14 2021 at nest KK 21 in colony De Kreupel island C, the Netherlands (5247.00 N 513.00 E). Ringer Leon Kelder.
ID uncertain: one parent is Caspian Gull cachinnans r[K.K], other parent unknown. Pictures of offspring p-FP strongly suggest Herring Gull influences in this nest.

Recoveries:
20-05-2021 IJsselmeer (De Kreupel), Noord-Holland, NL 5.247,00 N 513,00 E captured by ringer Leon Kelder
19-12-2021 Almere (De Vaart), Flevoland, NL 5.224,00 N 514,00 E colourring read Eric Roeland
27-02-2022 Wieringermeer (Zuiderdijkweg), Noord-Holland, NL 5.246,00 N 506,00 E colourring read Annelies Marijnis & Mars Muusse
16-04-2023 Almere (De Vaart), Flevoland, NL 5.224,00 N 514,00 E colourring read Eric Roeland
26-04-2023 Alkmaar (Vuiloverslag), Noord-Holland, NL 5.236,00 N 445,00 E colourring read Fred Cottaar
04-03-2024 IJsselmeer (De Kreupel), Noord-Holland, NL 5.247,00 N 513,00 E colourring read T. Horst & M. Muusse

Data for nest KK-2021:

Date: details:            
    egg no: width (mm): length (mm): volume (cm3): 
9-4-2021 1 egg in nest, cold.
https://waarneming.nl/observation/210432243/		 A egg 50.0 72.5  
           
23-4-2021 3 eggs in nest. egg no: width (mm): length (mm): volume (cm3): 
    B egg 51.6 74.0
    C egg 49.1 68.9
  A egg 50.0 72.2
metal: tibia: wing: head + bill: bill:  
Adult male trapped at nest. NLA 6.211.444 Red-K.K 459.0 124.2 53.8  
    mass: tarsus: moult score: bill height: grey scale Swob
    994 69.5 10x0 18.0 5.5 1086
   
14-5-2021 3 chicks in nest. metal: tibia: mass (gr): head + bill: tarsus:
  https://waarneming.nl/observation/214661812/ NLA 5.556.710 Pale FN 115 57.3 33.8  
    NLA 5.556.711 Pale F0 223 67.4 43.6  
    NLA 5.556.712 Pale FP 211 67.6 44.4  
   
20-5-2021 3 chicks in nest. metal: tibia: mass (gr): head + bill: wing:
    5556710 Pale FN 321 72.2 56.5
    5556711 Pale F0 517 85.2 94.5
    5556712 Pale FP 506 84.0 90.0

below: Caspian Gull cachinnans hybrid FP 4CY, March 04 2024, colony De Kreupel, the Netherlands. Picture: Thijs Horst & Mars Muusse.

below: Caspian Gull cachinnans hybrid FP 2CY, February 27 2022, gemaal Lely - Medemblik, the Netherlands. Picture: Mars Muusse.

Only one parent is certain, adult r-KK, which shows a broad medial band on P10. However, overall this adult may still fall within limits of cachinnans.

Offspring p-FP has obvious Herring-looks with pale inner hand, Herring headshape and bulbuous bill. This strongly indicates a hybrid male.

below: Caspian Gull cachinnans hybrid FP 1CY, May 14 2021, De Kreupel nest KK 21, the Netherlands. Picture: Leon Kelder.