Larus cachinnans in the Netherlands

(last update: December 24, 2021)

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

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Cachinnans breeding in the Netherlands - fecundity

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please send in your observations of colour ringed birds to: ring@buijsecoconsult.nl

CLUTCH SIZE

Table below: clutch sizes for Caspian Gull colony De Kreupel and colony Lelystad. Numbers of eggs in selected nests; selection of nests motivated HERE.
At least one parent scored as Caspian Gull (Larus cachinnans).

  Lelystad De Kreupel
clutch size: 2020: 2021: 2020: 2021:
3 eggs clutch 24 (92%) 35 (88%) xx xx
2 eggs clutch 2 (8%) 4 (10%) xx xx
1 egg clutch 0 (-) 1 (1+ eggs; 2%) xx xx
average ± SD 2.92 ± 0.27 2.85 ± 0.43 xx xx
(n) nests 26 40 xx xx

For complete tables with raw data, see HERE.

By far the majority (>90%) of Caspian Gull nests contain 3 egg clutches, with two exceptions in 2020.
Nest05 PLDP. We measured two eggs on April 15th, 2020 and the next visit (April 27th) the nest still contained just 2 eggs. Then the next visit was on May 7th, when we measured 1 chick (approx 1 week old) next to nest, the nest was empty.
Nest39. This is the nest of 'the one-legged bird', only found late in the season (June 2nd, 2020) when the eggs already showed tiny bursts in the shell.

Two nests were excluded from the analysis in 2020:
Nest38. Nest discovered relatively late in breeding season, on May 21st, 2020. Clutch size unknown, we ringed two pulli from this nest.
PairB. Both male and female are Caspian Gull, female with immature pattern on the bill. All season, every visit, they were just guarding from the look-out block at dam 1. Never really alarming, and we never found a nest. They may have used this as prospector season, or birds were floaters.

In 2021 >80% of the nests contained 3 eggs. Exceptions for 2021 are:
Nest43 r-FC. Nesting late in the season (2 eggs present on May 28th, 2021) and chicks ringed on June 26th, 2021.
Nest55. Throughout the season, only a female was observed at this nest with 2-egg clutch, which eventually failed.
Nest65. On April 24th, 2021 we found one Caspian Gull egg together with a goose egg in the nest. No subsequent visits to check if the clutch increased, we included this nest in the data set as '1+ eggs'.
Nest66. Nest in very dense Blackberry complex, which had 1 hatching egg and 1 complete egg on May 6th, 2021. We have no data on the initial clutch size earlier in the season.
Nest y-P:U60. This is a new breeder, 4CY female from Poland, with a 2-egg clutch.

We excluded these nest for the 2021 analysis:
Nest16. Early in the season a prospecting bird early in the season guarding at blocks, but no nest constructed.
Nest17B. Situation similar to nest 16 with prospecting female observed at this location, but no eggs were laid.
Nest33. Throughout the season, both parents were frequently seen guarding at the blocks, closely together, and no exact location of a nest (was there any in 2021?) was found in this dense section in the colony. Therefore, no clue for clutch size or fledging rate.
Nest42. Nest discovered late in season (May 28th, 2021) when we discovered a chick in an old Spoonbill nest (no eggs present), most likely Caspian Gull chick. Location of this nest on dam 2 is in concentration of both Spoonbills and Caspian Gulls, for which we skipped several visits.
Nest 044 was discovered late in season (May 28th, 2021) when a chick was found and ringed, situation like Nest42.

Table below: comparison of our Lelystad egg data with studies on Caspian Gulls (abroad: Germany, Poland, the Ukrain) and studies on Herring and Lesser Black-backed Gulls at Texel, the Netherlands (see thesis Camphuysen, p. 268-269). Foreign data will follow.

  Clutch size (n) nests 3-egg clutch volume (n) nests
Caspian Gull Lelystad 2020 2.92 ± 0.27 (26) 276,8 ± 11,9 (21)
Caspian Gull Lelystad 2021 2.85 ± 0.43 (40) 273,6 ± 17,8 (33)
Herring Gull 2006 Texel 2.71 ± 0.51 (42) 247.0 ± 23.3 (31)
Herring Gull 2007 Texel 2.58 ± 0.69 (55) 241.9 ± 24.1 (38)
Herring Gull 2008 Texel 2.86 ± 0.43 (69) 249.1 ± 22.4 (58)
Herring Gull 2009 Texel 2.69 ± 0.56 (65) 241.3 ± 23.5 (48)
Herring Gull 2010 Texel 2.81 ± 0.48 (58) 248.1 ± 20.2 (49)
Herring Gull 2011 Texel 2.77 ± 0.50 (56) 248.4 ± 21.0 (48)
Herring Gull 2012 Texel 2.64 ± 0.65 (73) 245.8 ± 24.1 (54)
Lesser B-b Gull 2006 Texel 2.75 ± 0.54 (57) 226.4 ± 17.1 (46)
Lesser B-b Gull 2007 Texel 2.73 ± 0.52 (79) 224.0 ± 17.1 (61)
Lesser B-b Gull 2008 Texel 2.84 ± 0.49 (98) 224.1 ± 15.1 (87)
Lesser B-b Gull 2009 Texel 2.80 ± 0.46 (114) 221.2 ± 17.6 (94)
Lesser B-b Gull 2010 Texel 2.80 ± 0.51 (88) 226.6 ± 15.7 (73)
Lesser B-b Gull 2011 Texel 2.82 ± 0.52 (88) 222.5 ± 20.5 (74)
Lesser B-b Gull 2012 Texel 2.59 ± 0.64 (97) 218.5 ± 17.5 (64)

VOLUME

Once a nest with eggs was located, eggs were marked with a letter 'A', 'B' and 'C'. All eggs were measured with calipers to the nearest 0,1 mm in width and length, unless there were signs (cracks or holes in the shell) of hatching chicks, then eggs were not measured.
Volume was measured by the formula also used by Camphuysen:  
Volume = k*L*W*W, with L=max length, with W = max width and k = a constant. We used k=0,5035. For motivation, see Camphuysen (p. 272).

Table below: egg dimensions and volumes for Caspian Gulls at colony Lelystad, breeding seasons 2020 & 2021, eggs/nest ranked on volume. Full set of data, see HERE.

  A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 73,1 50,7 94,5 71,6 50,2 90,9 70,3 49,6 87,1 274,8
SD 2,8 1,4 6,3 2,9 1,4 6,8 3,0 1,4 6,5 15,7
min 67,9 45,3 72,6 64,6 46,5 72,3 63,3 45,9 68,2 238,6
max 83,7 53,5 113,1 77,2 53,3 104,6 77,0 51,9 98,9 299,4
N 66 66 66 66 66 66 55 55 55 54

 

2020 2021
average    
SD 11,9 17,8
min 254,0 238,6
max 293,3 299,4
N    

Comparison of our Lelystad egg data with studies on Caspian Gulls (abroad: Germany, Poland, the Ukrain) and studies on Herring and Lesser Black-backed Gulls (Camphuysen, in the Netherlands). Will follow.

Table below: egg dimensions and volumes for Caspian Gulls at colony Perejaslav island reedbed (n: 16), Ukraine, breeding seasons 2009.

A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 73,7 50,0 93,0 72,4 50,2 92,1 71,1 49,8 88,9 274,0
SD 2,3 1,6 7,5 3,3 1,6 8,8 2,8 1,4 7,5 22,3
min 70,2 46,8 79,0 68,1 47,3 78,1 67,3 48,0 79,3 236,9
max 78,6 53,3 108,7 81,1 52,6 111,3 76,9 52,8 103,6 317,1
N 16 16 16 16 16 16 16 16 16 16

Table below: egg dimensions and volumes for Caspian Gulls at colony Perejaslav island reedbed (n: 14), Balyko-Schuchinka sand island (n: 8), Kyiv reservoir island (n: 16), all colonies in Ukraine, breeding seasons 2010.

A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 73,1 50,1 92,3 71,3 49,8 89,1 69,7 49,2 85,1 266,5
SD 2,7 1,8 7,8 2,0 1,6 6,9 2,4 1,7 6,9 18,9
min 67,9 43,6 70,3 67,1 46,6 77,6 63,7 46,0 72,8 223,4
max 78,4 53,5 109,2 75,1 52,8 104,3 73,7 53,9 101,1 303,9
N 38 38 38 38 38 38 38 38 38 38

Table below: egg dimensions and volumes for Caspian Gulls at colony Javoriv island near Lviv (n: 15), Perejaslav grass island (n: 19), Ukrainka reedbed (n: 7), all colonies in Ukraine, breeding seasons 2013.

A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 72,0 49,9 90,2 70,8 49,8 88,6 69,4 49,4 85,3 264,1
SD 3,0 1,4 7,0 2,6 1,5 7,2 2,7 1,4 6,4 19,6
min 66,4 46,2 79,7 66,1 46,7 77,1 64,3 46,3 71,3 236,3
max 79,6 53,1 107,1 77,0 52,7 107,1 75,9 52,1 101,3 315,5
N 41 41 41 41 41 41 41 41 41 41

Table below: egg dimensions and volumes for Caspian Gulls in Ukraine, breeding seasons 2016.

A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 73,2 49,9 92,0 71,1 49,5 87,7 68,8 49,5 84,8 264,5
SD 3,2 2,7 11,3 2,8 1,4 7,3 3,0 1,2 6,3 20,0
min 67,4 45,3 72,2 66,8 47,3 76,8 64,5 47,0 71,7 227,1
max 79,5 58,6 125,7 75,8 51,8 99,6 76,0 51,6 97,2 293,3
N 21 21 21 21 21 21 21 21 21 21

Table below: egg dimensions and volumes for Caspian Gulls at colony Ukrainka Damb (n: 38) & Ukrainka reedbed (n: 30) in Ukraine, breeding seasons 2020.

A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 71,8 49,6 89,2 69,8 48,7 84,5 68,2 48,4 80,4 254,1
SD 2,9 1,2 6,1 2,6 5,6 12,0 3,1 2,0 7,5 19,9
min 66,4 46,1 78,2 65,0 4,6 0,8 60,5 37,8 49,6 166,8
max 83,0 53,1 107,0 77,1 51,7 99,8 81,0 54,0 101,1 299,1
N 68 68 68 68 68 68 68 68 68 68

Table below: egg dimensions and volumes for Caspian Gulls in Ukraine (n: 184), breeding seasons aggregated 2009-2010-2013-2016-2020.

  A_length A_width A_volume B_length B_width B_volume C_length C_width C_volume TOTAL :
average 72,4 49,8 90,7 70,7 49,4 87,4 69,1 49,0 83,7 261,8
SD 2,9 1,6 7,6 2,7 3,6 9,6 2,9 1,8 7,5 20,7
min 66,4 43,6 70,3 65,0 4,6 0,8 60,5 37,8 49,6 166,8
max 83,0 58,6 125,7 81,1 52,8 111,3 81,0 54,0 103,6 317,1
N 184 184 184 184 184 184 184 184 184 184

HATCHING RATE

Relation number of eggs in the nest - chicks in the nest.

CHICK GROWTH

When chicks were caught for ringing, 'weight' and 'head+bill' were measured on May 21st, 2020. Results are in the table below:

nest: species linked to nest? colour ring metal ring Weight: Head+bill: Remarks
nest03 CACH Certain Noir F|R 5552903 323 79,90 Nest empty
nest03 CACH Certain Noir F|S 5552904 190 64,90
nest03 CACH Certain Noir F|T 5552905 208 80,07
nest29 CACH Certain Noir F|U 5552906 178 74,52 5 clutch, ABC eggs intact, but rotten
nest35 CACH Certain Noir F|V 5552907 186 65,49 1 egg intact and with embryo, but rotten
nest35 CACH Certain Noir F|W 5552908 265 73,70
Nest01 CACH & MICHA ? Certain Noir F|Y 5552910 230 68,63 Nest empty, signs of hatched chicks
Nest02 CACH Certain Noir F|X 5552909 264 74,44 Nest empty, signs of hatched chicks
Nest09 CACH & CACTUS Certain Noir F|Z 5552911 286 73,36 Empty nest
Nest09 CACH & CACTUS Certain Noir F|0 5552912 328 86,83
Nest06 CACH Certain Noir F|1  5552913 462 84,11 Empty nest
Nest06 CACH Uncertain Noir F|7 5552918 409 84,03 Chick found on the blocks, PESV alarming above so nest 6?
Nest21 CACH Certain Noir F|2 5552914 73 51,94 egg C not fertile - collected
Nest21 CACH Certain Noir F|4 5552915 154 62,92
Nest33 CACH Certain Noir F|5 5552916 513 86,64 Empty nest
Nest33 CACH Certain Noir F|6 5552917 611 89,84
Nest11 CACH Certain Noir F|8 5552919 686 94,00 Empty nest
Nest11 CACH Certain Noir F|9 5552920 513 86,85
Nest14 CACH Certain Noir F|+ 5552921 507 86,79 Empty nest
Nest14 CACH Certain Noir F|= 5552922 306 74,12
Nest25 CACH Certain Blue F|A 5552923 81 52,91 Empty nest
Nest25 CACH Certain Blue F|B 5552924 94 56,88
Nest17 CACH Certain Blue F|C 5552925 350 77,90 Empty nest
Nest32 CACH Certain Blue F|D 5552926 209 72,93 Empty nest, mole as a prey
Nest31 CACH Certain Blue F|E 5552927 73 51,25
Nest37 CACH Certain Blue F|F 5552928 227 71,90 New nest, both parents cachinnans, empty nest
Nest38 CACH & ARG Certain Blue F|G 5552929 98 57,78 New nest under a Sambucus nigra, mixed pair flying off and alarming above
Nest38 CACH & ARG Certain Blue F|H 5552930 203 67,42

Plotted in a graph below:

CANNIBALISM

Chick mortality in ther nest.

FLEDGING

Observations of fledged juveniles in colony late summer

Ring codes used in breeding season 2019, 2020 and 2021 for pulli at Lelystad. Fledging rate estimated from resightings in the period July 2019 - March 2022.
Note that numbers of resightings may strongly increase when adult birds turn back to the colony (>4CY).

In 2019 we ringed 12 chicks, of which 4 have been reported outside the colony up to March 2022 (this cohort is now 4CY March).
In 2020 we ringed 28 chicks, of which already 14 (=50%) have been reported (this cohort is now 3CY).
In 2021 we ringed 64 chicks, now also including some Herring Gulls, of which already 28 codes (>40%) were reported back. That is within 10 months after ringing.

SURVIVAL RATE

Mortality / survival rate - ringed juveniles become breeders

Results:

  • incubation period - will follow
  • mean date first egg - will follow
  • mean date hatching - will follow