Onmuf el aL • WHITE STORK NEST-SITE SELECTION AND BREEDING SUCCESS 359 
nearest stream in contrast to distance to a river, 
presumably because temporary streams do not flow 
dunng the entire breeding season and are small, 
possibly preventing White Storks from landing and 
taking off securely. 
The mean and the maximum altitudes of White 
Stork nests in our study area were much lower in 
elevation than reported by Tryjanowski el al. 
(2005b) where the maximum range in altitude was 
800 m. This difference may he due to lhe effect of 
slope on nesting sites as there was an increasing 
trend in the ratio of villages with nests with 
decreasing slope. Further data with larger sample 
sizes are required to lest this hypothesis. 
We did not find a relationship between breed¬ 
ing success and temperature in contrast to the 
work of Nowakowski (2006). This may be related 
to the temperate climate of our study area as the 
mean day and night temperature during April 
ranged between 7 and 15 C whereas in Now¬ 
akowski’s (2006) study it was 4-9 C. It is possi¬ 
ble that temperature may cause fluctuations in 
food resources (Denae 2006). We found a nega¬ 
tive correlation between breeding success and 
precipitation throughout the breeding season, 
while number of nests was positively correlated 
with precipitation, specifically in April. High 
precipitation in April may motivate White Storks 
to nest, but too much precipitation throughout the 
breeding season may have a negative impact 
either on success of the clutch or on chick deve¬ 
lopment (Moritzi et al. 2001). A negative impact 
of precipitation on breeding success was also 
found for Marabou Storks (Leptopiilos crumeni- 
for) in Africa (Monadjem and Bamford 2009). 
Denac (2006) reported that in sub-optimal habitats 
with poorer food resources, breeding success ol 
While Storks decreases with amount of rain and 
low temperature. 
The positive correlation between the number ot 
breeding pairs and total area of crop fields may 
be explained by the availability of new foraging 
resources for White Storks. It is common to see 
storks feeding behind tractors working in the field. 
The negative correlation between breeding suc¬ 
cess and total area of crop fields may be either due 
to confounding or intrapopulation competition 
between pairs (Nowakowski 2006. Nowakowski 
and Wasilewska 2006). The main commercial 
fruit production activity in the study area was lor 
tomatoes and red peppers; these agricultural pro¬ 
ducts are not included in the list ol suitable 
foraging sites for White Storks (Cramp and 
Simmons 1977). Thus, the negative correlation 
between fruit production ami number ot breeding 
pairs is predictable. We found no relationship 
between any of the analyzed breeding parameters 
and fallow lands. This could be either due to the 
small size of fields left fallow or the White Stork 
population in the region may not be affected by 
either existence or nonexistence of tallow' lands. 
The observed difference between the number of 
nests on electricity pylons and buildings between 
the central town and villages may be explained by 
several factors. First, on average buildings are 
taller than electricity pylons in the town and 
electricity pylons arc taller than houses in 
villages. A higher nest location may provide a 
better and more secure landing and takeoff site tor 
White Storks. Second, some villagers complained 
that White Storks brought live snakes to their 
nests anil some were able to escape and create 
problems for homeowners. Thus, some White 
Stork pairs trying to build nests on houses in 
villages may be disturbed by homeowners and 
build their nests on pylons. Further data and 
analyses are needed to test these hypotheses. 
The relatively small standard mean population 
density in our study area compared to Poland 
(Tryjanowski and Ku/.niuk 2002) may be due to 
fewer optimal and suboptimal habitats (Now¬ 
akowski and Wasilewska 2006). Data on the While 
Stork population in the central town suggest the 
population was significantly larger in the 1980s 
and declined after 1995. Local villagers suggest the 
White Stork population was much larger in 1970s 
and 1980s. A possible reason for this decline could 
be the dramatic loss of foraging sites on floodplains 
in the study area, as White Storks are highly 
vulnerable to wetland destruction in breeding areas 
(Dallinga and Schoenmakers 1989, Barbraud et al. 
1999). The quality and quantity of food that parents 
provide to their chicks is an important environ¬ 
mental factor influencing reproductive success 
(Kosicki et al. 2006). The historical wetland 
ecosystems in the study area were mainly charac¬ 
terized hy wide flooded areas for long periods 
during the spring. However, flood control measures 
were applied to 2.536 ha of the study area by the 
General Directorate of State Hydraulic Works 
(DSD between 1964 and 1995. converting these 
areas into farmland or dams which resulted in 
significant loss of wetland ecosystems. These 
losses may have contributed to the reduction in 
the number of breeding pairs and breeding success 
during the study period. 
