Larus cachinnans in the Netherlands

(last update: December 24, 2021)

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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

Lelystad:
nest y-PNED
nest y-PESV
nest y-PLDP
nest y-PHSV
nest y-P:A02
nest y-P:U60
nest zy-MT
nest r-FB
nest r-FC
nest 001
nest 003
nest 006
nest 009
nest 011
nest 012
nest 013
nest 014
nest 015
nest 016
nest 016B
nest 017
nest 018
nest 019
nest 021
nest 025
nest 027
nest 028
nest 029
nest 031
nest 032
nest 033
nest 034
nest 035
nest 036
nest 037
nest 038
nest 039
nest 040
nest 041
nest 042
nest 044
nest 045
nest 046
nest 047
nest 048
nest 053
nest 055
nest 056
nest 058
nest 060
nest 062
nest 063
nest 065
nest 066
nest 067
nest 072
pair A
pair B

Cachinnans breeding in the Netherlands - fecundity

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).

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.

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.

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.

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.

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.

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

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

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

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:

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