Table 1 Types of harness attachment methods used on migratory shorebirds

Abdominal implantation

Transmitter is surgically implanted into the intraperitoneal cavity of the abdomen by a veterinarian

Invasive and questionable in value given animal welfare implications

Requires specialist skills

Glue-on

Fur or feathers are clipped as close to the skin as possible to allow adhesion of a transmitter to the skin

Some studies have glued onto tail feathers but this only works for larger birds like seabirds

These are a very simple attachment method but have a very limited time frame of weeks or months depending on the timing of body moult. They are, therefore, only suitable for short-term studies [21]. This method has been commonly used for manual radio-tracking studies, and more recently for attaching GPS devices as part of studies on a variety of shorebirds in the Wadden Sea [1]

Harnessing

Transmitter is attached to the animal via a harness made from (usually) synthetic materials that are soft, which helps reduce abrasion to the skin. Knotting of material (and sometimes also gluing) or metal crimps are commonly used for securing the harness material to the transmitter. Considerations for choice of material include the addition to overall weight, the shape of the harness—whether it is round or flat and potential impacts on the bird, such as rubbing or restriction of movement

Harnesses affix devices to birds for relatively long periods of time and are therefore useful for studies of full migration

Most tracking devices have attachment points in the form of holes or hooks which can be adapted to different styles of attachments

Can have adverse impacts on the bird depending on type of harness and material used so need to be carefully chosen