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 - breeding ecology

PROSPECTING & AGE AT FIRST SETTLEMENT

At this moment, only few birds had been ringed before settling in this colony, therefore it is not possible to draw any conclusion yet. We did observe several breeding birds with obvious sub-adult features in wing and/or tail, either 4CY or 5CY birds.
We started the ringing program in 2020, we hope to see those ringed birds returning and settling at De Kreupel and Lelystad in the near future.

BREEDING DENSITY IN THE COLONIES

Population density in some sections of the colony may have repercussions and impact on chick survival rate. We have multiple observations and documentation of egg loss and chick mortality (cannibalism) in the densely populated colonies along the coast (colony Maasvlakte and colony Texel). Thus far, distances between nests don’t give rise to expect this happening much at Lelystad or De Kreupel. However, we have one sections with nests closely grouped together: nest 60-62-63 at dam – south section at Lelystad, and we may have to follow this cluster in more detail to see if this is relevant here. Maybe coincidentally, or not, we found a predated Caspian Gull egg at nest 62.

EGG LAYING DATE & HATCHING DATE

We assume the female lay three eggs within a 3 or 4 days period. (Check 1: % of birds in known studies like Camphuysen that do not get a 3-eggs clutch. Check 2: have deviations been described for the assumption that on three consecutive days there is a new egg?)
We use an average incubation period of 28 days, as described for Herring Gull in: The breeding biology of Herring and Lesser Black-backed Gulls on Texel, 2006-2010.
We used four methods to estimate laying date of eggs.

1. The ‘water test”. Eggs were placed in a small transparent plastic container, filled with water. The angle (from lying flat 0° to straight up 90°) and position (touching bottom container to floating) is an indication for development and age of the embryo inside the egg.
2. We coded several nests containing only one or two eggs (A-egg, B-egg). We used a permanent marker to write the ‘A’ and ‘B’ on the shell. If, in a next visit, the same nest contained a ‘full clutch’ of three eggs, we assume the new egg to be C-egg, and in retrospect, our last visit indicate the laying date. (pitfalls: see check 1 and check 2)
3. We witnessed small cracks in egg shells, indicating hatching date for a pullus. When using an assumed breeding period of 30 days, we are able to extrapolate the egg laying date. (Check 3: how many hours is a chick busy freeing itself from the shell? Do other, comparable studies have details on this? Check 4: what parameters may influence the total breeding time of 28 days and may this vary substantially from year to year? Check 5: what is the SD for the mean breeding period?)
4. In the first week after hatching, when chicks are still really small, you can estimate with relative good accuracy the hatching date for a chick, and, again, using the 28-days breeding period, you can estimate laying date (check 6: weakness of faults in twofold-assumption construction)

Hans Schekkerman kindly calculated egg laying date for the selceted nests in 2020 at Lelystad. The full excel is availble HERE. Conclusions are:

DEPARTING THE COLONY AFTER BREEDING

What date do parents leave the colony?
What date do juveniles leave the colony?

FLOATERS - DECISION NOT TO BREED

Observations of well prepared nests, but despite the energy put into this, the adults did not start breeding this season.

SITE FIDELITY - TIME SERIES

From pictures.

PARTNER FIDELITY - TIME SERIES

From pictures.

SYMPATRIC BREEDING - BETWEEN-SPECIES DYNAMICS

Territorial disputes and hierarchy.