Entanglement rates and their effects on the population

In order to be able to estimate the consequences for population development, individuals entangled by artificial nesting material in the nature reserve "Lummenfelsen" are to be recorded throughout the year between November 2018 and June 2020. Gannets and guillemots become entangled in the artificial nesting material and in most cases die because they cannot free themselves from the plastic residues. Several times during the summer months, surveys of the entangled seabirds have already been carried out sporadically by the Institute for Bird Research "Vogelwarte Helgoland" and regularly since 2014 by the FTZ as part of two F&E projects financed by the "Umweltbundesamt" (2014-2016: "Coherent monitoring of the pollution of German marine and coastal waters with human waste and the ecological consequences with further focus on in-depth identification of the sources", UFOPLAN 2014; 2017-2021: "Follow-up assessment and establishment of long-term monitoring of the pollution of various marine areas and biota by marine waste (marine litter)", UFOPLAN 2017) in the Heligoland colony. The existing data material is to be reviewed and supplemented by the above-mentioned surveys. Guillemots visit the breeding rocks irregularly from the end of October. At this time, the gannet nests are not occupied, so that the birds come even closer to the gannet nests, thus increasing the risk of entanglement. Every winter, a relatively high number of gannets die in this way, but quantitative data on this are still completely lacking.

Little is known about the effects of plastic waste as nesting material on seabird populations. For this reason, the recorded entanglement rates are to be incorporated in a population model to be developed in this research project, in order to see what effect the entanglement has on the population or will have in the future if the entanglement increases.

Data collection

During the recording period from October 2018 to September 2020, seabird entanglement in plastic trash was recorded three times a week in nine test plots using the same method each time.

Collected Data:

  • Date of entanglement, date of death of an individual/date of release of an individual, species of bird, number of individuals of affected species, condition of bird, type of plastic in which the bird was entangled, color of plastic, body part of entanglement, date when bird was no longer visible in rock


  • Scientific publication on the methodology of the data collection and the results of the field work during the period of data collection
  • Development of a population model (scientific publication and supervision of a master thesis)

Species and distribution
Seabird species affected by entanglement are the Northern Gannet, the Common Guillemot, and, with a few single individuals, the Black-legged Kittiwake. The entanglement hotspots are where the breeding grounds of Common Guillemot and Northern Gannet overlap (see graph). This "heat map" shows the density distribution of entanglement for one study area as an example. The darker the color, the more entanglement was recorded in this area.

Number of entanglements
Significantly more entangled individuals were recorded during the survey period than would be expected. The entanglement data, collected in this detail for the first time, yielded the following results, among others:

Gannets: 40-60 entangled individuals per year.
Common Guillemot: approximately 100 entangled individuals per year.

Gannet entanglement peak: July-September
Guillemot entanglement peak: April-June

Seasonal distribution of entanglement
For the first time, year-round entanglement was collected in a seabird colony. Accordingly, there are no data on entanglement victims in winter. The Guillemots visit the cliffs at irregular intervals for so-called "prospecting flights" even in the winter half-year. As a result, a not insignificant proportion of the annual entanglement of Guillemots occurs in the winter half-year:

Proportion of entanglement of Guillemots in winter:
Winter 2018/19: 29.73 %
Winter 2019/20: 28.42 %