Larus cachinnans in the Netherlands

(last update: December 24, 2021)

Coordinators:
Albert de Jong
Leon Kelder
Roland-Jan Buijs
Merijn Loeve
Mars Muusse

Home

Cachinnans breeding in the Netherlands - scoring breeding bird phenotypes

you can participate in this project too!
please send in your observations of colour ringed birds to: ring@buijsecoconsult.nl

PHENOTYPIC CHARACTERISTICS OF BREEDING CASPIAN GULL AT LELYSTAD 2020 & 2021

Every Lelystad visit in 2020 and 2021, we photographed breeding birds, both partners at the nest, both standing and flying as much as possible.
From the images we scored all birds to determine taxon / species, using traits mentioned in Gibbins, Neubauer & Small 2011.
For 2020, the complete set of images was scored by Albert de Jong and Mars Muusse seperately, then put together and checked for differences in 'total score'.
The total scores resulted in 'conclusion' on species ID, and fortunately, conclusions were very close for either Albert or Mars.
For 2021, the complete set of images was scored by Mars, and also included below.

Chris Gibbins, Grzegorz Neubauer & Brian Small - British Birds 2011

The individual trait scores sum to a 'total score'. Classification is:
- score 4 to 12 = Caspian Gull
- score 9 to 20 = Hybrid
- score 12 to 20 = Herring Gull

selected nests - species composition Lelystad 2020 2021
Caspian Gull 37 59
Caspian Gull sub-adult (not scored) 5 0
Caspian or hybrid (outside Herring range) 2 3
Herring or hybrid (outside Caspian range) 4 5
Herring Gull 2 5
Yellow-legged Gull 0 1
Hybrid Yellow-legged x Herring Gull 0 1
Breeding bird not scored (no pictures) 6 12
total n = 56 n = 86

species composition Lelystad of selected nests (table above)

  • This is NOT the species composition for the whole colony, this is the compostion ONLY for selected nests
  • As described earlier: nests were selected for:
    - one/both of the birds guarding at lookout post seemed to be cachinnans
    - a nests was built / eggs were present very early in the breeding season indicating cachinnans
    - shell pattern of eggs & egg dimensions indicated cachinnans
    - or (very often) a combination of these 3 points
  • For 2020, we estimate 44 Caspian Gulls or Caspian Gull hybrids in colony Lelystad
  • For 2020, 85% (44 out of 50 scored birds in the sample) are classified Caspian Gull or Caspian Gull hybrid
  • For 2021, we estimate 62 Caspian Gulls or Caspian Gull hybrids in colony Lelystad
  • For 2021, 80% (62 out of 74 scored birds in the sample) are classified Caspian Gull or Caspian Gull hybrid
selected nests - pair composition Lelystad 2020 2021
Caspian Gull pure pair 16 24
Caspian Gull with hybrid (outside Caspian range) 4 2
Caspian with Herring Gull 2 3
Caspian with Yellow-legged Gull 0 1
Hybrid (zy-MT) with Herring Gull 0 1
partner(s) not scored (no pictures) 6 12
total pairs n = 28 n = 43

pair composition Lelystad of selected nests (table above)

  • This is NOT the pair composition for the whole colony, this is the compostion ONLY for selected nests
  • Nest selection criteria for this sample: see above
  • For 2020, we estimate at least 22, but up to to 28 nests involving Caspian Gull or Caspian Gull hybrid in colony Lelystad
  • For 2021, we estimate at least 30, but up to to 42 nests involving Caspian Gull or Caspian Gull hybrid in colony Lelystad

general notes & remarks

  • The ideal situation for us as researchers: guarding breeder + partner present, easy to photograph together, having a full clutch early in the season, with egg dimensions and patterns indicating Caspian Gull.
    Easy peasy. Sometimes that happens, e.g. nest y-PA02, nest 29, or y-PHSV.
  • Fortunately, we have nests with both partners present "all the time" (seemingly). But in some nests not, and despite many visits we didn't manage to document a partner sufficiently.
    You find this situation in the table under "Breeding bird not scored (no pictures)". How is that possible?
    Examples are nest 17, with a female Herring Gull present all the time, but a partner never present (suspected Caspian Gull).
    Or nest 55 with a perfect female Caspian Gull, but the partner was never seen, litterally. This nest failed eventually, so maybe there just "was no partner" for her?
  • Sometimes, a pair guarded a location "notoriously often". Why didn't they start to breed? Are these prospectors? Floaters maybe?
    In 2020 we had such a couple, both perfect Caspian Gull, called PAIR B. Litterally "always on their lookout spot".
    Also in 2020, a Yellow-legged Gull bonded with Herring Gull g-97, called PAIR A. Always present, but not building a nest (as far as we know).
    In 2021, again a mixed pair, now Yellow-legged Gull with Caspian Gull, always present at dam 2. And it took ages to start nest 41, which almost immediately failed.
    Also worth mentioning is nest 60 - 62 - 63, very close together, with several Herring Gull nests within 3 steps distance, and a nice Blackberry complex for hiding the chicks, to picture the situation.
    Nests this close together proved difficult to monitor, therefore uncertainties in the table with scores, below. Best option seems to trap breeding adults at the nest in 2022, and ring these birds.
  • Some nests we just had to let go. For example, a bird deep down in a Blackberry complex (nest 16B). Or close to Spoonbills (nest 40).
    Illustrative is nest 53, of which we have no certainty about the parents. But we managed to ring chicks, which were reported back (see link).
    They nest at T-split dam 1, a 'challenging' situation: loads of Lesser Black-backed Gull nest here, deep down between blocks, invisible from the canoe, and close to a dense Spoonbill section.

SCORING TABLES

Trait 1: P10 overall pattern, white to black ratio - 0 less black than white

.

- 1 approximately equal black and white
. - 2 more black than white
Trait 2: white tip P10 - 0 clear white, no signs of black
. - 1 small dark spots on one or both webs
. - 2 incomplete subterminal bar (two large black spots, one on each web or an unconnected bar, broken in the middle)
. - 3 complete subterminal bar
Trait 3: P10 tongue - 0 white or whitish
. - 1 greyish, paler than mantle
. - 2 same shade as mantle
Trait 4: extent of black on P5 - 0 black on both webs connected, forming band, black of equal depth on each web
. - 1 black on both webs connected, forming band, black on outer web deeper than inner
. - 2 black on both webs, but isolated spots (= incomplete bar)
. - 3 black on outer web only
. - 4 no black
Trait 5: extent of black on P4 - 0 black on both webs 
. - 1 black  on one web only
. - 2 no black
Trait 6: iris peppering - 0 dark-looking, >50% covered by dark spotting/peppering
. - 1 moderately dark, with 10–50% of the area spotted
. - 2 single or very few dark spots (area <10%)
. - 3 no dark spotting on iris
Trait 7: orbital ring - 0 dark/deep orange to red
. - 1 pale to moderately orange
. - 2 yellow
Trait 8: bill dimension - 0 very long and slim, with little/no visible gonydeal angle (L:D ratio >2.8)
. - 1 slim, slight gonydeal angle (ratio 2.4–2.79)
. - 2 intermediate (ratio 2.0–2.39)
. - 3 short and deep, well-marked gonydeal angle (ratio <2.0)
Trait 9: legs - 0 long
  - 1 moderately long
  - 2 short

RAW DATA 2020

Traits Trait 1 Trait 2 Trait 3 Trait 4 Trait 5 Trait 6 Trait 7 Trait 8 Trait 9 total score conclusion:
  Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars Albert Mars .
Nest 01                    
#1 male 2 1 1 1 ? 1 0 0 2 2 3 2 0 0 2 2 ? 1 10 10 Caspian or hybrid (outside Herring range)
#2 female 2 2 1 2 2 2 1 2 2 2 3 2 1 0 2 2 1 1 15 15 Hybrid (outside Caspian range)
Nest 02
#1 PNED 1 0 1 1 ? 0 0 0 2 2 1 0 0 0 1 1 1 1 7 5 Caspian
#2 0 0 0 1 ? 1 1 1 2 2 1 1 0 0 1 2 2 1 7 9 (probably) Caspian
Nest 03
#1 0 0 0 0 0 0 2 2 2 1 2 1 0 0 1 2 1 0 8 6 Caspian
#2 0 0 0 0 1 0 0 2 2 2 2 1 0 0 0 1 1 0 6 6 Caspian
Nest 05
#1 PLDP 0 0 0 0 ? 0 0 0 0 2 2 2 0 0 1 2 1 0 4 6 Caspian
#2 0 0 0 0 ? 0 0 0 0 2 2 1 0 0 0 1 1 1 3 5 Caspian
Nest 06
#1 PESV 1 0 1 1 ? 0 1 0 2 2 2 2 0 0 1 2 1 1 9 8 Caspian
#2 0 0 0 0 0 0 0 0 2 2 2 2 0 0 1 1 0 0 5 5 Caspian
Nest 08
#1 XLDT 0 0 1 1 0 1 1 1 0 2 2 0 0 0 1 2 0 1 5 8 Caspian
#2 0 1 0 3 ? 2 1 1 1 1 2 2 0 0 1 2 0 1 5 13 Probably hybrid (almost outside Caspian range)
Nest 09
#1 0 0 0 0 ? 0 0 0 2 2 3 1 0 0 3 2 1 1 9 6 Caspian
#2 2 1 3 3 ? 2 1 0 0 2 2 1 0 0 3 2 2 2 13 13 Hybrid (almost outside Caspian range)
Nest 11
#1 female 2 1 3 3 ? 0 0 0 2 2 2 1 0 0 1 2 1 1 11 10 Caspian
#2 male 2 1 3 3 ? 0 1 0 1 1 2 0 0 0 1 2 ? 1 10 8 Caspian
Nest 12
#1 Both birds obviously sub-adults, hence not scored like adults. Images show nice Caspian Gulls.
#2
Nest 13
#1 2 1 3 3 ? 0 1 0 1 1 1 1 0 0 2 1 ? 1 10 8 Caspian (or hybrid)
#2 No pictures.
Nest 14
#1 0 0 0 0 ? 0 1 0 0 2 2 1 0 0 1 1 0 0 4 4 Caspian
#2 0 0 0 0 0 0 1 0 0 1 2 1 0 0 1 1 1 1 5 4 Caspian
Nest 15
#1 2 2 0 0 2 0 1 1 2 2 3 1 0 0 1 2 1 1 12 9 Caspian
#2 0 0 0 0 ? 0 2 2 2 2 ? 1 0 0 0 1 1 1 5 7 Caspian
Nest 16
#1 2 2 1 2 ? 1 0 0 1 1 1 0 0 0 1 3 1 1 7 10 Caspian
#2 2 2 3 3 ? 1 0 0 2 1 ? 1 ? 0 ? 2 ? 1 7 11 Caspian
Nest 17
#1 1 0 1 1 0 0 0 0 2 2 ? ? ? ? 4 3 Caspian
#2 1 0 1 1 ? 0 0 0 2 2 2 1 0 0 1 1 1 2 8 7 Caspian
Nest 18
#1 0 0 0 1 ? 0 1 0 2 2 1 0 0 0 0 1 1 1 9 5 Caspian
#2 No pictures.
Nest 21
#1 Bird obviously sub-adult, hence not scored like adults. Images show nice Caspian Gull.  
#2 0 0 0 0 ? 1 0 0 2 2 2 1 0 0 1 2 ? 1 5 7 Caspian
Nest 25
#1 Bird obviously sub-adult, hence not scored like adults. Images show nice Caspian Gull.        
#2 0 0 1 1 ? 1 1 0 1 1 0 0 0 0 1 2 ? 0 4 5 Caspian
Nest 29
#1 0 0 0 0 1 0 2 2 2 2 3 2 0 0 1 1 ? 2 9 9 Caspian
#2 0 0 0 0 1 0 0 0 2 2 ? 1 0 0 1 2 ? 1 4 6 Caspian
Nest 31
#1 Bird obviously sub-adult, hence not scored like adults. Images show nice Caspian Gull.
#2 No pictures.
Nest 32
#1 ? 0 0 1 ? 1 1 1 2 2 0 0 0 0 1 1 0 0 4 6 Caspian
#2 No pictures.
Nest 33
#1 0 0 3 3 ? 1 1 0 1 1 2 1 0 0 1 1 ? 1 8 8 Caspian
#2 Pictures insufficient for scoring.
Nest 34
#1 0 0 0 0 ? 0 1 0 2 2 0 0 0 0 1 1 1 1 5 4 Caspian
#2 No pictures of an open wing, hence no scoring. In every respect classic Herring Gull? female Herring
Nest 35
#1 0 0 0 0 1 1 0 0 2 2 0 0 0 0 1 0 1 1 5 4 Caspian
#2 0 0 0 0 ? 0 1 0 1 1 3 2 0 0 1 0 1 1 7 4 Caspian
Nest 36
#1 0 0 0 0 ? 1 1 0 2 2 0 0 0 0 1 1 1 0 5 4 Caspian
#2 2 0 1 1 ? 1 0 0 2 2 3 2 0 0 2 1 2 2 12 9 Caspian
Nest 37
#1 0 0 2 3 1 1 0 0 2 2 3 2 0 0 1 1 0 0 9 9 Caspian
#2 0 0 0 1 ? 1 0 0 2 2 3 2 0 0 1 1 1 0 7 7 Caspian
Nest 38
#1 1 0 0 0 ? 1 0-1 0 2 2 3 2 0 1 1 3 1 2 8 11 Caspian Herring backcross?
#2 2 2 3 3 ? 2 2 2 2 2 3 3 1 0 2 2 2 1 17 17 Herring
Nest 39
#1   1 3 1 0 2 2 0 1 1 11 Hybrid (outside Herring range)
#2 No pictures.
Pair B
#1 1 1 1 1 ? 1 0 0 2 1 0 0 0 0 1 1 1 0 9 5 Caspian
#2 ? 0 1 1 ? 1 1 0 2 2 0 0 0 0 0 0 1 0 5 4 Caspian

RAW DATA 2021 (scoring Mars)

sheet 2021 Lelystad trait 1 trait 2 trait 3 trait 4 trait 5 trait 6 trait 7 trait 8 trait 9 total conclusion: site and/or partner fidelity
nest01 male 1 1 0 0 2 1 0 2 0 7 Caspian same as 2020
female 0 1 0 2 2 2 0 0 1 8 Caspian possibly same; was subad in 2020
nest02 male 1 1 0 1 2 0 0 2 ? 7 Caspian same as 2020
female PNED 0 1 0 0 2 0 0 1 1 5 Caspian same as 2020
nest03 male 0 0 0 2 2 2 0 2 0 8 Caspian same as 2020
female 0 0 0 0 2 2 0 1 ? 5 Caspian same as 2020
nest05 male PLDP 0 0 0 0 2 2 0 2 ? 6 Caspian same as 2020
female 0 0 0 0 2 2 0 1 ? 5 Caspian different bird
nest06 male 0 0 0 0 2 2 0 2 0 6 Caspian different bird
female 2 0 1 1 2 3 1 3 2 15 Herring different bird
nest11 male 1 3 1 0 1 1 0 2 ? 9 (probably) Caspian same as 2020
female 0 1 0 2 2 0 0 2 2 9 (probably) Caspian same as 2020
nest12 male 0 1 0 1 1 0 0 2 0 5 Caspian probably same; was subad in 2020
female 0 1 1 0 2 2 0 2 0 8 Caspian probably same; was subad in 2020
nest13 male 1 0 0 0 2 1 0 2 ? 6 Caspian same as 2020
female not known  
nest14 male 0 0 0 0 1 1 0 2 1 5 Caspian same as 2020
female 0 0 0 0 2 1 0 1 1 5 Caspian same as 2020
nest15 male 2 0 0 1 2 1 0 2 1 9 (probably)  Caspian same as 2020
female 0 0 1 2 2 1 0 1 0 7 Caspian same as 2020
nest16B male 0 1 0 0 2 0 1 1 1 6 Caspian ? 16-2020, minor differences in wingtip pattern
female not known
nest17 male cachinnans type, no pictures
female 2 3 1 1 2 3 1 3 2 18 Herring different bird
nest18 male 0 1 0 0 2 0 0 1 1 5 Caspian same as 2020
female 2 2 1 2 2 2 0 2 1 14 Hybrid (outside Caspian range) unknown
nest19 male 0 0 1 2 ? 0 0 2 0 5 a 7 Caspian new nest
female 0 1 1 0 1 1 0 1 0 5 Caspian new nest
nest21 male 0 1 0 0 0 1 0 2 0 4 Caspian probably same; was subad in 2020
female cachinnans type, no pictures  
nest29 male 0 2 1 0 2 1 0 1 0 7 Caspian same as 2020
female 0 0 0 1 2 2 1 1 0 7 Caspian same as 2020
nest33 male 2 3 1 0 1 0 0 1 0 8 Caspian subadult, different bird
female 0 0 0 0 2 1 0 1 1 5 Caspian same as 2020
nest34 male 0 0 1 0 2 0 0 1 1 5 Caspian same as 2020
female 2 1 2 4 2 2 2 2 2 19 Herring same as 2020
nest35 male 0 0 1 0 2 1 0 0 1 5 Caspian same as 2020
female 0 0 0 0 1 2 0 2 0 5 Caspian same as 2020
nest38 male 0 1 0 0 2 1 0 2 0 6 Caspian 60% likely same as 2020
female 2 1 2 0 2 2 0 3 1 13 Hybrid (outside Caspian range) same as 2020
nest40 male 0 1 0 1 2 0 0 2 0 6 Caspian new nest, 5CY
female argentatus type, no pictures
nest41 male 2 2 2 1 2 2 0 2 2 15 Yellow-legged new nest
female 0 0 1 0 1 2 0 2 1 7 Caspian new nest
nest43 male rFC 1 2 1 2 2 1 0 2 0 11 Caspian new nest
female 0 0 0 0 2 1 0 2 ? 5 a 6 Caspian new nest
nest44 male 2 3 1 1 1 3 0 3 14 Hybrid (outside Caspian range) new nest
female not known 
nest46 male 0 0 0 0 2 2 0 1 0 5 Caspian same as nest 37 -2020
female 0 3 1 0 2 2 0 2 0 10 Caspian same as nest 37 -2020
nest47 male 0 1 0 0 1 1 0 0 0 3 Caspian new nest
female not known  
nest48 male 1 2 0 1 1 0 0 1 1 7 Caspian new nest
female 2 2 2 3 2 2 1 3 2 19 Herring new nest
nest52 male PLDP 0 0 0 0 2 2 0 1 0 5 Caspian same as 2020
female 0 0 0 0 2 2 0 2 ? 6 a 7 Caspian likely different bird, 2020 bird had white prim covs
nest53 male ? 0 ? 0 ? 0 0 1 1 2+ Caspian new nest & unsufficient photographic documentation
female not known
nest54 male zy-MT 2 3 2 0 2 3 0 2 2 16 hybrid Yellow-legged x Herring new nest
female 2 0 2 3 2 3 1 3 2 18 Herring new nest
nest55 male not known
female 0 0 1 2 2 0 0 0 0 5 Caspian new nest
nest56 male 1 1 0 1 1 2 0 2 ? 8 a 9 Caspian new nest
female 0 0 0 1 2 0 0 1 ? 4 a 5 Caspian new nest
nest57 male P:A02 1 0 0 0 2 1 0 1 0 5 Caspian new nest
female 0 1 1 2 2 2 0 0 0 8 Caspian new nest
nest58 male 1 3 1 0 2 3 0 1 0 11 Caspian 5CY, new nest
female 0 3 0 1 0 0 0 1 ? 5 a 6 Caspian 4CY, new nest
nest60 male 0 0 0 3 2 1 0 2 0 8 Caspian new nest
female 0 0 0 1 2 1 0 1 ? 5 a 6 Caspian new nest, probable partner
nest61 male 2 2 1 0 2 0 0 0 0 7 Caspian new nest, 5CY
female rFB 0 0 0 2 2 0 0 1 0 5 Caspian new nest
nest62 male not known
female 1 1 1 2 2 3 0 2 1 13 Hybrid (outside Caspian range) new nest
nest63 male not known  
female 2 3 2 1 1 3 0 3 2 17 Hybrid (outside Caspian range) new nest, 4CY
nest64 male 0 0 0 2 2 1 0 2 0 7 Caspian new nest
female PHSV 0 0 0 1 2 2 0 1 0 6 Caspian new nest
nest65 male 2 3 0 1 1 0 0 1 ? 8 Caspian new nest, 4CY
female 2 3 2 1 2 0 0 0 ? 10 Caspian new nest, 4CY
nest66 male not known  
female 0 1 0 1 1 1 0 1 1 6 Caspian new nest
nest67 male 0 0 0 0 1 2 0 1 ? 4 a 5 Caspian new nest
female 2 3 ? 1 0 0 0 1 ? 7 a 11 Caspian new nest, 4CY
nest68 male ? 1 ? ? ? 1 0 0 0 2 a 6 Caspian new nest
female P:U60 2 3 1 0 1 1 0 1 1 10 Caspian new nest, 4CY