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 - methods

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

SELECTING NESTS AT DE KREUPEL & LELYSTAD

Lesser Black-backed Gulls and Herring Gulls breed in good numbers at De Kreupel or Lelystad.
How to be sure a nest belongs to Caspian Gulls? We use the following steps.

  • guarding birds at potential nest location
    Obviously, Caspian Gull is a relatively early breeding species, and many birds arrive in March. Guarding birds normally choose obvious posts, visible from a distance. Furthermore, birds attract attention by frequently alarming in a characteristic way ("albatrossing") and with diagnostic long-calls. Normally, the nest is within 10 meters.
  • egg laying date
    Some sections of the colony were visited by foot, the birds alarming overhead. Then, a strong indication for Caspian Gull presence are the eggs. Egg laying date is obviously early for bulk of the breeding Caspians. We have collected data for egg laying date at colony Lelystad in season 2020 and season 2021. Result will be in the section BREEDING BIOLOGY.
    Results for Lelystad 2020:
    - average egg laying date for 21 selected Caspian nests is April 7th.
    - average hatching date for 21 selected Caspian nests is May 9th.
  • egg dimensions & pattern
    Third, shell pattern on eggs is a good clue, being more contrasting (than Herring) and eggs are larger (than Herring).
    Nests of Lesser Black-backed Gulls contain much smaller and browner eggs, and egg laying date is weeks later for that species.

These 3 steps combined divide late species (Lesser Black-backed & Herring Gull) from early species (bulk of the Caspian Gulls & hybrids).
In step 2, we selected nests without certainty of parents. Still, we could confirm Caspian Gull as parents for these early nests by subsequent observations and photographs. The method proved to work.

  • examining photographs
    Many birds, alarming overhead, were photographed and details on head and wingtip were used to classify birds using the Chris Gibbins criteria (British Birds). Therefore, first estimations for the population size are assumed to be pretty accurate.

 

TIME SCHEDULE

Late March: first impression of the colony before breeding started.

  • From the kayak, we roughly estimated numbers and locations of cachinnans nests.
  • Do birds occupy approximately the same locations for their nests, as they did in 2019? -> Definitely.
  • Can we easily get to the nests from the kayak? -> Not always. Tip for 2021: None.
  • Estimate disturbance for vulnerable species (Spoonbill, Little Egret). Tip for 2021: acceptable time in colony can increase, based on 2020 results?

Mid-April: research starts in 1st survey.

  • Locate nests, from the kayak,  from the water. Landing. Searching between blocks and vegetation.
  • Nest with eggs? -> mark nest with long bamboo stick and coded flag. Tip for 2021: Has to be more obvious from the water. And flag has to be really close to the nest, together with an obvious marked/coded block well visible from waterfront, especially in clustered areas.
  • Measure eggs in mm.
  • ‘Water test’ to determine laying date.
  • Check for prey left-overs.
  • Take picture of nest and location. Tip for 2021: use plasticised paper binder with images of exact nest location + immediate surrounding.
  • Add GPS fix to nest location database. Tip for 2021: any improvements for accuracy?
  • Any alarming adults overhead, especially when diving to us: take pictures of that adult.

Late-April: 2nd survey.

  • Trace marked nests. Check eggs, and measure new eggs as  described in mid-April. Tip for 2021: cut away Blackberry stems in 1 m diameter of nest.
  • Do ‘water test’ to determine laying date.
  • Check for prey left-overs.
  • Locate new nests, from the kayak,  from the water. Same procedure.
  • Mark new nests, with long bamboo stick and coded flag.
  • Take pictures of adults, especially shots for wingtip pattern.

Early-May: 3rd survey.

  • Much emphasis on pictures of adults.
  • Visit nests to check progress. Tip for 2021: cut away Blackberry stems in 1 m diameter of nest. Tip 2 for 2021: supply wooden fruit box?
  • Check for prey left-overs.
  • If chicks present: measure weight.
  • If chicks vomit: take picture of pellet.
  • Locate new nests of late starting cachinnans. Check: how could we miss these nests in previous survey? Tip for 2021: check all the exact old locations of 2020. We have paint sprayed the codes on the blocks in red and white (hopefully it will last all winter). Also, we now have accurate GPS for all old 2020 nests.
  • Minimise disturbance of vulnerable species. Tip for 2021: if we remain this careful, it’s okay with the Spoonbills and Egrets.

Mid-May: 4th survey and ringing chicks.

  • Ring chicks. Tip for 2021: how to increase relocate the chicks when they hide?
  • Ring chicks. Check for 2021: do we need an extra day for ringing, e.g. around May 10th?
  • Locate marked  nests and search chicks. Tip for 2021: chicks appeared pretty large already and hard to find in Blackberry vegetation. Can we supply wooded box for both shelter and safe haven, which will make it easy to catch juveniles by mid-May?
  • Measure weight of chicks.

Early-June: 5th survey.

  • Allocate ringed chicks to nest code. Tip for 2021: how to increase observations of ringed chicks in the colony?
  • Determine ringed chick - parent relation (to confirm: did we ring the right chicks?). -> This proofed to be very difficult, as almost all chicks hided in the dense vegetation. Tip for 2021: Improve data on relations. How ???
  • Photograph the adults in flight.

Early-September: 6th survey.

  • Visit the abandoned colony. Check nest locations and check GPS fixes.
  • Paint spray code on the blocks next to the nest, to ease the search for next season.
  • Remove all bamboo sticks.
  • Check nests for prey left-overs.
  • Check for dead chicks or check for rings.

Research, general ideas.

  • Do we need to visit the colony more often?
  • Is there a possibility to monitor the colony from the waterfront (385 meters away)?

RESEARCH DATA.

Research data - egg laying date and hatching date.

  • Incomplete nests (1 egg , 2 eggs) indicate laying date, when 3rd egg is present in next visit.
  • Water test: extrapolation for laying and order of laying (A, B, C-egg).
  • Compare data with cachinnans from Germany, Poland and the Ukrain.
  • Compare data with Dutch research on argenteus and graellsii.
  • Observations of wet chicks, cracks in egg shells.
  • Weight of chicks in the first week.

Research data - egg dimensions.

  • Size to nearest 0,1 mm in width and length. Volume by formula Stonehouse 1964.
  • Compare data with cachinnans from Germany, Poland and the Ukrain.
  • Compare data with Dutch research on argenteus and graellsii.

Research data – breeding success.

  • Early stage breeding – eggs disappeared from nest?
  • No signs of chicks, throughout the 2nd half of the season. -> Especially sub-adult breeders seemed inexperienced to maintain the nest?
  • Witness predation. -> Not witnessed at all in 2020 in this colony.
  • Fledged juveniles in the colony. -> A few ‘brothers/sisters’ without ring were seen accompanying ringed chicks on June 2nd 2020.
  • Observations of ringed birds outside the colony. -> We create a website to illustrate the research and hope this will increase data on movements of our birds.
  • General, for 2021: How can we get a better picture of chick survival in this densely vegetated colony?

Research data: adults.

  • Score adults on cachinnans trades as in Gibbins. -> Scored separately by Albert and Mars, then compare outcome.
  • Monitor mixed breeding with argenteus. Tip for 2021: extra effort to monitor these nests and trace down chicks for ringing.
  • Tip for 2021: tape record alarm and long callings from known individuals? -> Extra ID support?
  • Dedicate more time to ‘funky nests’? Like 2020 nest with 5 eggs, which exactly were the true parents?

Research data – emigration, immigration and dispersal.

  • Origin of breeding birds? -> Check for ringed birds that have a nest.
  • Origin? -> Take blood samples of breeding adults? Important question: could we trap breeders without unacceptable disturbance of vulnerable species? Major pro: adults will be ringed, adults will be blood sampled, wingtip patterns from in-hand images.
  • Relative abundance of cachinnans compared to other taxa. Time series analysis. -> Increase of one species correlates with decrease of another? -> Complete colony survey on breeding numbers.
  • Observations of ringed birds outside the colony. -> We create a website to illustrate the research and hope this will increase data on movements of our birds.

Research data, general ideas.

  • Should we trap and ring breeding adults to collect more data on adults?
  • Should we increase ringing chicks from coded nests? If yes, how?
  • In 2020 no (detailed) monitoring of other gull species in the colony. Should we do such in 2021?
  • Should we intensify / combine research Leystad – De Kreupel? If yes, which fields of research?

Methods:

  • early stage - monitor breeding birds, plot nests, take pictures of wingtip patterns,
  • breeding season - visit nests, ring adults, collect pellets,
  • late stage - estimate breeding succes, ring pulli,

Measurements for adult cachinnans, as proposed in the Polish research.

Cachinnans is a new breeding species for the Netherlands, hence no research has been done for the species here. Yet, in Poland and Belarus it's an expanding species, which has colonised the interior for the last 3 decades and prolonged research has been going on in these countries. We join this research, and have chosen to follow an the same strategy and methods to make data comparible.

In 2021 we trapped breeding (sub)adults ate the nest and scored these birds. All phenotypics were taken and you can find data for these birds by clicking the trhumbnails at the right hand side of this page.

Caspian Gull cachinnans adult, April 27 2020, Lelystad, the Netherlands. Picture: Albert de Jong. Albatrossing to the partner flying overhead. We placed long bamboo sticks to relocate nests in tall vegetation.
Measuring angle of egg to determine laying date.
Nest 35, April 16 2021 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).

All visits to the breakwaters by kayak, May 16 2019 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).

Ringing of Caspian Gull Larus cachinnans, May 21 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Ringing of Caspian Gull Larus cachinnans, May 21 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Yellow-legged Gull michahellis male x Herring Gull argenteus 97 8CY female, but nest was never located (always on this post). June 02 2020, Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E). Herring Gull 97 was ringed as 4CY on September 15 2016 at Brouwersdam, the Netherlands.

Nest 034, with male Caspian Gull Larus cachinnans and female Herring Gull Larus argentatus argenteus. May 07 2020, Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).

Nest 029 with 5-eggs clutch. May 07 2020, Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).

Caspian Gull Larus cachinnans F|X 1CY, May 21 2020, Lelystad, The Netherlands (52°30'36.17"N 005°25'11.70"E). Picture: Merijn Loeve.
Bird hatched at
"nest 02" in season 2020.
Caspian Gull Larus cachinnans F|X 1CY, May 21 2020, Lelystad, The Netherlands (52°30'36.17"N 005°25'11.70"E). Picture: Merijn Loeve.
Measurements on this bird, hatched at
"nest 02" in season 2020.
Caspian Gull Larus cachinnans F|5 1CY, September 19 2020, Portugal. Picture: Rui Viana.
Bird hatched at
"nest 33" in season 2020 and already in Portugal by September.
Nest 15 code sprayed on the block again in fall. Nice illustration of increase of vegetation over the season, in which it is hard to locate chicks. "Somewhere down there should be the nest!", September 11 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Collecting bamboo sticks and code nests after the breeding season, September 11 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
New codes on the blocks for the nests after the breeding season, September 11 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Nest 14 and a satisfied coordinator, September 11 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Nest 05 code sprayed on the block again in fall. Hopefully still visible when season 2021 starts. September 11 2020 at Lelystad colony, the Netherlands (52°30'36.17"N 005°25'11.70"E).
Trapping breeding (sub)adults at the nest to attach colour tibia rings: ringers Roland-jan Buijs & Leon Kelder. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Head dimensions of breeding (sub)adults. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Grey tone of upperparts in breeding (sub)adults. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Measure weight of breeding (sub)adults. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Wingtip patterns in breeding (sub)adults. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Coordinator for cachinnans research at De Kreupel, ecologist for Staatsbosbeheer: Leon Kelder. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Ringer for cachinnans research at De Kreupel & Lelystad, ecologist for Buijs Ecoconsult: Roland-Jan Buijs. April 23 2021, De Kreupel. Picture: Merijn Loeve.
Merijn Loeve holding a Polish cachinnans which just received it's new red tibia ring. April 23 2021, De Kreupel. Picture: Leon Kelder.