Monitoring breeding outcome

For this phase, it is of utmost importance that the timing of visits to the nest is undertaken according to best practice, i.e. at times when the risk of disturbing the adult birds is minimal. Visits should not be undertaken in adverse weather conditions (i.e. cold, wet or excessively hot). For some species, it is even recommended that no visits should be done during the egg stage of the breeding season (Hardey et al. 2013).

The raptor worker tries to establish clutch size, brood size and fledging success, using the minimum number of visits required to establish these parameters. Often a visit during the chick stage is combined with the ringing of the chicks. For this, the person must be a licensed ringer (ringing permits issued by BTO on behalf of SNH),  following best practice described in Hardey et al. (2013) and BTO’s “Ringers’ Manual” (Redfern and Clarke 2001).

Finally, a visit around or just after the chicks are expected to fledge will reveal the number of fledglings from each nest. This visit should involve a nest inspection to check if any chicks might have died at the later stages of the breeding attempt. This is an important part of the monitoring, as it will give the final piece of information of the outcome of the breeding attempt.

Data collected during the nest monitoring phase includes, apart from clutch size, brood size and fledgling numbers, the type of nest (e.g. nest box, tree or cliff), nest site (e.g. species of tree) and if ringing occurs, the age, sex and size (e.g. wing and tarsus length as well as body mass) of the chicks. Thorough recording of visit dates is again essential, as it will indicate stages and even specific dates when a potential nest failure might have happened.

For more detailed species-specific information please refer to Hardey et al. (2013).