Coastal breeding birds in the Netherlands

To make the information in this report more accessible to site managers, policy makers and other stakeholders, we created a brochure for OBN Knowledge Network and the VBNE (Association of Forest and Nature Reserve Owners).

Coastal breeding birds naturally breed along the edges of dynamic intertidal areas, such as on islands, spits, beaches and salt marsh zones. These are all areas that are highly dynamic and vegetation is constantly changes due to erosion and sedimentation. The dynamic nature of these areas influences the breeding opportunities and breeding success of birds, especially as the suitable breeding sites comes and goes.
Over the past century, many of the natural breeding areas of coastal birds have disappeared or become unsuitable. The Delta Works and the closure of the Zuiderzee and the Lauwerszee have had a large-scale effect on the dynamics of Dutch estuaries. This has also led to ground predators being able to establish themselves permanently in the breeding areas of coastal birds. A strong increase in human activities in these areas has also had a significant impact on the populations of coastal breeding birds.

Keeping coastal areas suitable for breeding birds requires specific habitat development and management measures as well as great dedication from site managers. Major challenges include vegetation succession, predator effects and disturbance by human activities.

The breeding habitats of coastal birds essentially consists of bare sandy ground (possibly with shells, gravel, etc.), with a very low vegetation cover and plants that do not grow much higher than about 50 cm. The development of plants and plant communities is largely controlled by dynamics and abiotic conditions on site.
The extent to which an area is actually suitable for breeding and raising young also depends on the presence of predators (ground-based and/or gulls), predation pressure on clutches and young, food availability in and around the breeding area and human activities in the area.

In our research we discuss Sandwich tern, Arctic tern, common tern, little tern, avocet, Kentish plover and ringed plover. There are subtle but important differences in behaviour and habitat preferences between these species. Sandwich tern, Arctic tern and common tern breed in colonies (Sandwich terns very compact, common tern and Arctic tern often somewhat more dispearsed). Avocet and Kentish plover prefer loose, open colonies or solitary nesting. The ringed plover always nests solitarily.

In addition, each species has preferences in openness and the amount of vegetation in an area. Kentish plover and little tern prefer extremely bare and open areas in which vegetation is almost completely absent. Arctic tern, avocet and ringed plover nest in areas where chicks can hide from danger in scattered clumps of vegetation. Common terns and Sandwich terns also breed in open, bare areas, but are generally more tolerant of increasing vegetation cover and higher herbaceous vegetation, with chicks again using the vegetation for shelter. In addition, common terns also use artificial structures such as pillars near locks and pontoons. The avocet in particular is dependent on soft mud for foraging. This must be available at a short distance from the nesting sites for both adult birds and slightly older chicks. Young chicks first hunt for insects on the surface, but soon switch to sifting in soft mud.

The measures discussed in our research have been an attempt to serve multiple coastal breeding bird species simultaneously. Sometimes measures are needed for one specific species, in which case extra attention must be paid to the species-specific requirements of that species. These species-specific requirements are described in detail in the appendix to the research report.

There are many options available for both the construction and development of new areas and the management of existing areas for coastal breeding birds. But which is the right option? In our research, we advocate a step-wise approach: when choosing the location for new areas or the management and development of existing areas, try to make as much use as possible of the natural dynamics or control this with variable water levels, preferably with brackish or salt water.
Only if construction in dynamic environments or the application of dynamics in existing areas is not possible, can more intensive management measures be considered. This involves all kinds of vegetation management, the use of new substrate, shell layers or salt, electric fences against ground predators and the control of human co-use by, among other things, deploying volunteers.