The results of the censuses of the species show a high variability depending on the methodology applied. Census reliability is crucial to establish an appropriate diagnosis of the status of populations and their trends.

Censuses provide the principal reference to evaluate the conservation status and the population trends of lesser kestrels, and it is crucial that the methodology employed is sufficiently precise to ensure an objective diagnosis of the situation of the species and its evolution.

Urban habitats require a specific methodology different to that of rural zones, where usually colonies are established in isolated buildings in the countryside making it easy to count the number of birds. The complexity of urban areas, the towns and villages, makes census work more difficult, given the different types and heights of the buildings which often impede the observation of the birds, to follow their flight and to localise nests. In some cases, the population is spread across numerous buildings or with nests situated in sites difficult to see. Therefore, it is necessary to establish a census methodology adapted to urban areas. 

The literature review has shown that the application of different census methodologies can sometime impede the comparability of results. Indeed, currently there is no single agreed methodology for the species between the different working groups and those responsible for populations censuses, which is considered as a priority in the “Lesser Kestrel Action Plan in the European Union”.

In this action there will be an objective evaluation of which will be the most precise methodology to census the populations of lesser kestrels in urban centres with respect to the different variables that could affect the result.

For this, two different reference situations characteristic of urban SPAs in Extremadura will be used: colonies situated in a single building and colonies spread across several buildings.

Colonies will be selected where the precise number of existing pairs will be known, where different censuses will be carried out to look at the incidence of different variables in their effectiveness. The aim is to identify the census that is most precise and establish the best conditions to quantify the populations of the species in urban settings, and to optimise the costs of these actions in the future.

The general methodology will be to count individuals at a distance, to avoid any disturbance of the birds. Prior to egg-laying, the pairs normally are established in the nest sites and enter frequently, so that it is easy to locate and count the number of pairs present in the colony. This method can be used at later stages in breeding, adding numbers of pairs to the initial pre-laying count, since when pairs are feeding young, the size of the colony can be underestimated since only pairs that have not failed in their breeding attempt will be counted. This method is also useful as a means to produce diagrams mapping the colony on the buildings.

With respect to the variables that can potentially affect the effectiveness of the census method, the following will be evaluated:

  • Date of census. From the pre-laying, the majority of the breeding birds are already in the colony. Afterwards, once laying starts, at least one of the pair from each nest should be at some time or other be at the breeding colony.
  • Time of census. The middle part of the day should be avoided because the lesser kestrels will have left the colony at these times to forage. It is expected that the most effective time to do a census is during the first hour of day light which is when most birds are at their nests defending their territories. The effect of this variable will be tested by carrying out at each colony two visits on consecutive days, one of those in the morning and the other in the afternoon in order to compare the effectiveness of the census at each moment during the day.
  • Time of observation by colony or building (relationship between length of observation and effectiveness). The census should be carried out for a period that is related to the size of the colony, but usually it can be considered sufficient if no new pair has been detected during 30-40 minutes of observation. To test this, censuses will be undertaken following this rule and others stopping after 10 minutes after not detecting a new pair.
  • Area to census. This variable is already considered when looking at the two different types of colonies.
  • Experience and previous knowledge of the colony by the observer. The censuses of colonies will always be carried out by one or two observers with previous experience and knowledge of the same colonies and with one or more observers with less experience and who do not know the colonies.
  • Pre-determination of observation points (yes/no)

The censuses will be carried out by project technicians from the General Directorate of the Environment (DGMA), DEMA, Terra Naturalis, as well as members of the Scientific Committee (action F2). In addition, Environment agents and technicians from DGMA, as well as volunteers, may participate at no cost to the project.

All observers will be given prior training in the methodology of the work and the objectives behind the analysis of the variables. The DGMA will set the dates and protocols for the census based on what is agreed by the Scientific Committee of the project.

Responsible for implementation: General Directorate of the Environment, DEMA and Terra Naturalis.