Population size and spatial distribution of the white storkCiconia ciconiain Poland in 1958 with insights into long-term trends in regional and global population

Abstract

Although white stork Ciconia ciconia counts go back to the XIX century, making the species a model in population investigations, substantial gaps remain in the knowledge of its large-scale population dynamics. In particular, incomplete past estimates from the core breeding areas leave the long-term changes uncertain. In this paper, we provide the earliest estimation of population size and spatial distribution of the white stork in its main stronghold (Poland) to reconstruct the species long-term trends. Based on original survey data collected during the 2 nd (1958, incomplete in Poland) and 3 rd (1974, successful) International White Stork Census (IWSC) we compared stork numbers in a random sample of villages surveyed on both occasions. We applied linear models to estimate the population growth rate between 1958 and 1974 and to assess spatial variation in population change across the country. Finally, we collated worldwide stork numbers obtained from all IWSCs and discuss the long-term population trends in light of new data. The stork population in Poland in 1958 was estimated at 46,100 breeding pairs and the nationwide density at 14.7 pairs/100 km 2 . A strong decline (by 30.2%, 1.88% per year) was noted between 1958 and 1974 across Poland with prominent spatial variation reflecting differences in local densities. The strongest declines in absolute terms affected the most abundant populations in Eastern Poland. Our data show that in the mid-20th century, the stork population in Poland was close to the current level, but it experienced a massive decline during the 1960s-1980s. This decline was consistent with trends in the worldwide and regional European populations, contrary to earlier statements indicating limited, if any, changes in the core European area. Overall, our data expand knowledge on the long-term dynamics in the white stork numbers and show that even massive changes may easily go undetected if based on non-solid data.

The usefulness of unmanned aerial vehicles (UAV) in white stork censusing

“…Although it is not surprising, as the access to a nest for humans watching from the ground level is more constrained than for a flying object recording from above, so far, the method of counting stork fledglings was assumed precise enough even when amateurs performed the survey. Thus, it has been used long term and worldwide (Wuczyński et al 2021). Results of our simple experiment bring essential information that during the long-term censusing of the white stork population, the overall breeding output may be underestimated when only ground checking is performed.…”

“…We performed white stork nests census according to the standard methodology used in white stork monitoring, which constitutes counting juvenile storks standing on the nest that are not able to fly yet, but developed enough to be considered fledglings (Wuczyński et al 2021). This method is assumed reliable and not observer-biased, particularly when performed by experienced observers.…”

“…Among these species is the white stork Ciconia ciconia, which has been monitored in some locations for over 100 years (Bairlein 1991). More importantly, the monitoring is being performed on the entire breeding range under the International White Storks Censuses according to standardised methodology, which enables the assessment of current trends on broad time and geographical scales (Wuczyński et al 2021). The white stork is an example of an easily recognisable species that does not demand high expertise during censusing, its monitoring can be performed even by amateurs, and the observer bias is believed to be low.…”

The usefulness of Unmanned Aerial Vehicles (UAV) in white stork censusing

“…We conducted the study in two distinguished populations of the white stork differing in ecology and facing different environmental conditions. One, near the town of Augustów in NE Poland (N 53.85, E 22.98), where the population density is high, namely 44 breeding pairs/100 km 2 , and the landscape is composed of traditionally managed agricultural lands with a mosaic of grasslands (meadows and pastures), arable elds and woods (Zbyryt et In 2019 (between 1th and 2th July), according to the standard methodology of white stork censusing (Wuczyński et al 2021), we surveyed 57 white stork nests in NE Poland. One experienced observer who knew well the study area (AZ -co-author of this paper) recorded the number of edglings using binoculars 10x42.…”

“…Among these species is the white stork Ciconia ciconia, which has been being monitored in some locations for over 100 years (Bairlein 1991). More importantly, the monitoring is being performed on the entire breeding range under the International White Storks Censuses according to standardised methodology, which enables the assessment of current trends on broad time and geographical scales (Wuczyński et al 2021). The white stork is an example of an easily recognisable species that does not demand high expertise during censusing, and its monitoring can be performed even by amateurs.…”