Sessions

Territory-based turnover – the possible changes of breeding parents at one territory – provides information about the joint effect of breeding dispersal and mortality, both of which are important parameters for conservation biology. Investigating these population dynamic variables is essential for monitoring globally threatened raptors, such as the saker falcon (Falco cherrug), a strictly protected, emblematic breeding species of Hungary. Despite many conservation efforts, its population is stagnating or even decreasing in certain areas, urging researchers to study the possible reasons for this phenomenon.

Our aim was to infer possible territory turnover events in Hungary between 2023 and 2025. One way to determine territory turnover in monogamous species is by calculating the difference of the within-year mean relatedness and the between-year mean relatedness of offspring in the same territory, which equals to the relatedness change between years. Certain thresholds are established to determine whether there was no turnover (<0.25, chicks are full siblings), only one parent changed (>0.25 & <0.5, chicks are half-siblings), or both parents changed (>0.75, chicks are not related).

To estimate relatedness, we needed a reliable and highly polymorphic microsatellite marker set specifically for the saker falcon population of Hungary. To gain the genotype data needed, we took axillary feather samples from 120 chicks during the ringing process. Using this DNA, we tested a total of 23 microsatellite markers, ten of which were originally developed for the saker falcon, twelve for the peregrine falcon (Falco peregrinus), and one for the Eurasian goshawk (Accipiter gentilis). Out of these, 18 proved to be adequate. We also optimized PCR conditions for the marker set to minimize the number of reactions, so the 18 markers ran in two monoplex, five duplex, and two triplex PCR reactions.

The microsatellite marker set’s high polymorphism was sufficient for individual identification, supported by a very low probability of identity value (PI=5.7x10-20), even among siblings (PSIB=8.5x10-8). We found an average of 8.7 alleles per locus, which did not differ from Hardy-Weinberg proportions and were in linkage equilibrium. Consequently, satisfyingly precise relatedness estimation was possible. We estimated the turnover of 15 territory pairs, from which we detected two turnovers of both parents, two one-parent turnovers and eleven instances of no turnover. This results in a 20% turnover rate.

Overall, this turnover rate can be considered relatively low, thus we can conclude that a higher proportion of breeding pairs remain in their territory in consecutive years, therefore the rate of breeding dispersal and mortality is relatively low in the studied population. To reveal the reasons for turnover events and the future direction of conservation measures, more territories and ecological variables should be included in prospective analyses.