Whitewater kayaker and ornithology expert, Bor Mihelič, who was a part of the BRT5 crew for the entire descent of the Sava River, performed a bird census in the nesting season of the entire 258 km of Sava River in Slovenia that we paddled – the first continuous survery of this kind.

His data and findings were a base for diploma thesis Celosten popis gnezdilk reke Save s pomočjo kajaka (Comprehensive inventory of nesting birds of the Sava River with the help of a kayak), which he successfully defendend on December 22nd 2023 at BCN – Biotehniški center Naklo. Survey findings and results now provide a base of data, that ornithologists can compare with future surveys of this kind, which can, in a long term, serve local conservation groups to further protect stretches of the Sava.

Abstract of the thesis
In Slovenia, bird monitorings are only carried out during the breeding season for individual river areas or for individual target species. No systematic inventory of the whole river during the breeding season has been carried out in Slovenia. Most river inventories are conducted from land, where the passability and opacity of the terrain often make inventories difficult. In this thesis we aimed to conduct a comprehensive waterbird census of the Sava River by kayak and to determine the feasibility, efficiency and utility of this type of nesting census. We wanted to estimate the size of the nesting populations along entire length of the Sava River and to compare the species composition and abundance of nesting birds in free-flowing sections and in accumulations on the river.

The whole area of the Sava River in Slovenia was surveyed and inventoried by kayak between 1st June and 11th June 2021. All waterbird species and species that may be associated with the riverbed for breeding were inventoried. For each species, we recorded the location, the number of individuals and the breeding codes found. We assessed their populations on the Sava River based on counts and species ecology. The Sava River was divided into 18 sections according to the free-flowing course of the river or the stagnant flow of the reservoirs. For each section, the diversity was determined using the Shannon and Simpson indices. We tested for differences between reaches using the chi-square test.

We were able to inventory all 251 km of the river. We inventoried 1972 individuals of waterbirds and river-associated birds belonging to 24 species. The most abundant species were: mallard (N=414), goosander (N=229) and grey wagtail (N = 223). We detected a colony of the cormorant, which has not been registered as a breeding species on the Sava River so far. The sections with free-flowing water had a similar diversity as the hydropower reservoirs, but the species composition differed. The reservoirs had fewer species of nature conservation importance, which leads us to conclude that the contribution of the flowing water sections of the Sava to the conservation of threatened bird species is greater than that of the reservoirs. We have confirmed that the kayak can be used to carry out a good quality river inventory.

You can reach the entire diploma HERE.

This proves BRT5 provided a unique opportunity to monitor the entire stretch of Sava in Slovenia for waterfowl in the nesting period in one go, by a kayak. Exploring rivers can combine enjoyment with serious scientific survey, which provides a detailed insight into the functionality of the riverine ecosystem and thus objective arguments for its protection.