The HELCOM common monitoring relevant on white-tailed sea eagles is described on a general level in the HELCOM Monitoring Manual in the sub-programme: Marine bird health.
In addition to the annual monitoring described in the Monitoring Manual, data are collected from eagles found dead in nature. Such specimens belong to the state in all countries around the Baltic Sea, except for in Germany. This provides good opportunities for investigations of the cause of death. State game is normally sent to the national authority for registration and examination of death cause, saving of samples and preparation for museum collections. Professional investigations of causes of death in white-tailed sea eagles are performed in Finland, Germany and Sweden (and possibly elsewhere). Before being opened, all white-tailed sea eagles are inspected macroscopically for body condition and signs of trauma, and x-rayed to assess the presence of lead shot, fractures etc. Distributions of cause of death of sea eagles from Germany, Finland and Sweden are presented in Herrmann et al. (2011). In Finland, Germany and Sweden, organ samples are archived from all reasonably fresh specimens.
The monitoring activities relevant to the indicator that are currently carried out by HELCOM Contracting Parties are described in the HELCOM Monitoring Manual in the Monitoring Concepts table.
Sub-programme: Marine bird health
Monitoring Concepts table
Current monitoring, which is carried out by the HELCOM Contracting Parties on an annual basis, is considered adequate.
At present, eagles are breeding along the coasts of almost the whole of the Baltic Sea, as well as in inland freshwater systems within the Baltic Sea catchment area. Populations and reproduction are monitored in a network of national projects that use the same methodology (Helander 1990). Monitoring of white-tailed sea eagle reproduction in Sweden has been included in the National Environment Monitoring Programme since 1989 as an indicator of the effects from chemical pollutants. Pre-1954 background data on breeding success and pre-1950 background data on nestling brood size are available from the Swedish Baltic coastline (Helander 1994a, 2003a). These data are used as reference levels for evaluation of observations within the programme (see below). The current numbers of known territorial pairs in the HELCOM coastal area are given below (Monitoring table 1). The coastal area is restricted to the 10 km from the coastal zone, with the majority of eagles breeding close to the coastline and in the archipelagos.
White-tailed sea eagles breeding inland in freshwater habitats are usually monitored in the same way as the coastal populations. Freshwater populations are much less exposed to contaminants and observed differences in data can be used to compare exposure to different pressures faced by inland and coastal eagles (Helander et al. 2002).
Monitoring table 1. The number of breeding white-tailed sea eagle pairs monitored and considered in the indicator evaluation. Note: this table has not been updated during the 2018 update process. Some numbers presented here are now outdated, as sea eagle populations have increased.
During spring (February – April, incubation period) eagle territories are checked from a safe distance (to avoid disturbance) in order to locate occupied nests. Occupied nests are to be revisited during the nestling period (May – June) for assessment of breeding success and nestling brood size.
It is crucial for the assessment of breeding success and productivity that unsuccessful as well as successful breeding attempts are recorded equally well. Most breeding failures occur during the early phases of the breeding cycle. The early spring surveys are therefore very important as later during the breeding season there is an increasing risk that unsuccessful breeding attempts are overlooked. A very effective way to perform the early survey in spring is by helicopter. The importance of conducting a first check during the incubation period, to be followed by a second check during the nestling period, has been stressed previously by Postupalsky (1974; 1981; 1983), Steenhof (1987) and Steenhof & Newton (2007).
For the assessment of nestling brood size, it is crucial that the nest content is checked properly by climbing to the nest (or a neighbouring tree) in order to be able to look into the nest. Nests checked only from the ground are not used for assessment of nestling brood size. The number of nestlings in successful nests observed only from the ground is estimated by applying a correction factor before being used for calculation of productivity. For the future, Unmanned Airborne Systems (UAS) may provide good opportunities for the checking of unclimbed nest to assess actual nestling brood size.