Active protection of endangered species of Charadriiformes on the Vistula River islands: implementation of selected protection tasks in the area of SPA ""Dolina Środkowej Wisły""

Description

Since 2000, the threat level for Charadriiformes nesting on the Vistula River has increased. The key threat for adults and offspring is predation by American minks and foxes. As a result, breeding success of gulls and terns nesting on river islands is close to zero, and adult mortality is high. The giving up grazing after 2004 led to fast loss of nesting sites for terns and Mew Gulls. Long periods of hydrological drought in recent years have accelerated this process. For Mew Gulls, another factor has a negative impact on reproduction - low intra-population genetic diversity, leading to higher hatching failure (e.g. Bukaciński et al 2018).

We propose (a) to reduce the numbers of American minks (trapping and euthanasia) and foxes (shooting), (b) to neutralize the pressure of those predators and livestock near breeding areas by electric fencing (for colonies) and through a procedure involving the use of incubators and dummy eggs (for single nests), (c) to renew breeding habitats by grazing; and in the case of Mew Gulls also (d) to increase genetic diversity within colonies by exchanging of clutches between nests distant from each other.

The long-term goal of the project is to stop the population declines of key species in the middle Vistula riverbed bird community: first of all Mew Gulls - the species currently considered the most threatened with extinction in Poland.

Regional Directors for Environmental Protection in Warsaw and Lublin responsible for managing Natura 2000 SPA Dolina Wisły Środkowej PLB140004 will benefit as our protection measures are consistent with Plans of Protection Tasks for this area. All private and public entities or NGOs working for nature protection can implement the proposed protective measures in other areas inhabited by Charadriiformes or other ground-nesting species.

Summary of project results

The Vistula is one of the last large rivers in Europe that has retained the features of a natural lowland river over a large area. The braided nature of the riverbed means that in the middle section of the Vistula we can observe habitats that are very difficult to find in the inland of Western Europe as a result of stream regulation. These are primarily islands and sandy shoals in the riverbed and steep banks. The uniqueness of this environment results from the currently rarely recorded species diversity of avifauna (over 160 species recorded; Chylarecki et al. 1995), but above all from the presence of species typical for large lowland rivers little changed by man. The core of the bird community of the middle Vistula riverbed is formed by Charadriiformes, including several species of gulls, terns and plovers that inhabit mainly islands and sandy shoals in the riverbed (Bukaciński and Bukacińska 2015, Bukaciński et al. 2017). This place is of absolutely exceptional importance for the Common Gull Larus canus and the Little Tern Sternula albifrons, maintaining 75-90% of their breeding populations in Poland. It is also crucial for the Common Tern Sterna hirundo, the Mediterranean Gull Ichthyaetus melanocephalus, the Ringed Plover Charadrius hiaticula and the Oystercatcher Haematopus ostralegus, being a breeding ground for at least 25-35% of the national population. Slightly less important for the Little Ringed Plover Charadrius hiaticula and the Black-headed Gull Chroicocephalus ridibundus, maintaining annually about 10-15% of the breeding population of each of these species (Sikora et al. 2007, Bukaciński and Bukacińska 2015). A natural consequence of the concentration of a large part of the breeding population in one place is that the fate of the birds nesting there (breeding success, survival of adults, etc.) significantly influences the status and abundance of the species throughout the country. This is the case of the above-mentioned species, most of which have shown a clear decreasing trend in their numbers in the Vistula Valley in recent decades.

During the last two decades, the threats and the level of pressure that Charadriiformes nesting on the Vistula River experience, have changed completely. While until 1999 the greatest threat were outbreaks of blackflies (bloodsucking insects from the Simuliidae family), large river floods, and locally also cattle grazing, already in the years 2000-2004 the absolutely key threat to both offspring and adult birds was the rapidly increasing pressure of American minks Neogale vision and red foxes Vulpes vulpes (Bukaciński and Bukacińska 2000, 2001, 2003). As a result, the breeding success of gulls and terns nesting on the Vistula islands was increasingly zero or close to zero, and the mortality of adults was extremely high (Buczyński 2000, Bukaciński and Bukacińska 2008). In the years 2005-2015, the pressure of American minks and foxes continued to grow, and we also increasingly noted the presence of the Raccoon Dog Nyctereutes procyonoides. The cessation of intensive cattle grazing after 2004 resulted in the dynamic disappearance of optimal breeding habitats for terns and common gulls. In the last four years, before the project began (2016-2019), in areas not covered by active protection, mammalian predation was still a key threat to broods and adult gulls and terns. Long periods of hydrological drought further accelerated vegetation succession, activated mass outbreaks of black flies, and above all, facilitated the penetration of islands by humans, feral dogs and cats (Bukaciński et al. 2015, 2018, Drzyzga 2015, Kot et al. 2017, Pikulska 2017). In the case of the Common Gull, we are dealing with another important phenomenon that negatively affects reproduction, related to the rapidly decreasing number of birds on breeding grounds. It is the low intra-population genetic diversity of birds (Bukaciński et al. 2000). This leads to increased unhatchability and low immunity of hatchlings (Buczyński 2000, Bukaciński and Bukacińska 2003, 2015, Spottiswoode, Moller 2004).

The strategic, long-term goal of active conservation measures was to stop the decline in the population of key species of the middle Vistula riverbed community: primarily the Common Gull - a species currently considered to be most endangered in Poland (a decline in population by over 80% in 2007-2020; Chodkiewicz et al. 2019, Wardecki et al. 2021, Przymencki et al. 2024) and the Little Tern, Common Tern and Black-headed Gull, which, like the Common Gull, are experiencing a decline in population (by 20-40% in 2007-2020), as well as the Mediterranean Gull, which joined the group of declining species only in recent years (Sikora et al. 2007, Chodkiewicz et al. 2018, Chylarecki et al. 2018, Bukaciński et al. 2018, Bukaciński et al., unpublished material). Even immediate and extremely effective protective measures will not stop the trend immediately. This requires, first of all, effective implementation of detailed intra-seasonal goals, which we will present below, and the time needed for the chicks that survive to reach sexual maturity (2-4 years), return to the hatching sites on the Vistula and successfully breed every season. The specific, intra-seasonal aimes were: (a) to reduce the mortality of adults on the breeding grounds (to several individuals per season in the area covered by conservation measures), (b) to increase the breeding success (by no less than 20-40%), and in the case of the Common Gull also (c) to increase the genetic diversity of birds within the colony (reducing the frequency of unhatched eggs to the level of 10-15% of laid eggs). We have taken active protective measures to cover the broods and nesting grounds of the following species: Common Gulls, Mediterranean Gulls, Black-headed Gulls, Little Terns, Common Terns, and Oystercatchers, which is still very rare in Poland. Indirectly, effective protection was also provided to the following species nesting in the same nesting grounds: Ringed Plovers, Little Ringed Plovers, and Lapwing Vanellus vanellus, which is currently, like the Common Gull, one of the most endangered species in the country (Chylarecki et al. 2018).

As part of the implementation of active conservation measures on the breeding grounds and broods of 6 bird species threatened with extinction: Common Gulls, Mediterranean Gulls, Black-headed Gulls, Little Terns, Common Terns and Oystercatchers inhabiting the Natura 2000 SPA Dolina Wisły Środkowej (PLB140004) on a section of the river between Puławy and the mouth of the Pilica (km 371-457 of the Vistula shipping route) in an area of ​​approx. 9460 ha (inter-embankment area with an average width of 1100 m x 86 km = 9460 ha), the following activities were carried out:

a. Reduction of the number of predatory mammals, including catches of American minks in live traps with bait and euthanasia. We conducted four catch campaigns every year, including two in the autumn-spring period. In selected locations (near the most important breeding grounds), catches were also conducted in the spring-summer period (May-July). During each action, depending on environmental conditions (ice, floe, water level) and the activity of predatory mammals, catches were conducted for 14-21 days.

b. Red fox shooting (work carried out by hunting associations) along the entire section of the river covered by the protection activities, in the area adjacent to the river, on both sides of it throughout the year, excluding the closed season (from April 1 to June 30).

c. Protection of bird breeding grounds using an electric fence system. A few fences were set up annually on the most important nesting grounds. In the unregulated Vistula River, a mobile fencing system proved to be excellent (completely different from the so-called electric shepherds used for fencing pastures). It is a lightweight, relatively easy to assemble, construction that can be rolled up rather quickly. Regardless of the fact that the system is installed only for the breeding season (early April - late June/July), in the event of high water levels, the lightweight construction ensures quick dismantling and the possibility of immediate transport from the islands to safe places outside the riverbed. Each individual net system was connected to an electric generator and a battery, which was additionally reinforced by a solar panel.

d. Protection of eggs using incubators and egg dummies. This is a task consistent with the previous one, complementing and strengthening its effect. The procedure was extremely important, especially for birds which nested solitarily or in loose associations and were not fenced with an electric grid system. Shortly after being laid, eggs of such pairs were taken away and wooden dummies were placed in their nests, the size, shape and colour of which resembled the original eggs of a given species. The original eggs of gulls and terns were transferred to incubators, where, while maintaining the appropriate temperature and humidity, they were safely! incubated. Eggs were returned to the same nests from which they were taken out shortly before hatching. In this way, during the incubation period, eggs were protected (in incubators) from mammalian predators. What is more, American minks and red foxes, as sniffers, do not recognize artificial eggs as potential food, and they rarely disturb adults on the breeding grounds. In order to carry out this task, two incubators and two hatchers were purchased.

e. Enhancing genetic diversity in colonies of the Common Gull. The method of increasing the genetic diversity within smaller colonies/populations was technically simple and logistically uncomplicated. It consisted in the mutual exchange of eggs between nests spaced apart by no less than a dozen or (better) several dozen kilometers.

The only measurable way to monitor the effects of protective measures carried out in the middle Vistula is to monitor changes occurring in the environment. As part of this task, monitoring of the reproductive ecology of protected bird species was carried out, which included: the mortality rate of adult birds on breeding grounds, basic parameters of breeding biology and ecology (causes of nest failures, hatching success, breeding success). In addition to breeding ecology monitoring, the number and distribution of all breeding gulls, terns, waders, ducks and species of steep banks (Sand Martin, Common Kingfisher, Goosander) were monitored annually on the entire protected section of the river. The basis was two or three trips, combined with pedestrian exploration of all islands in the riverbed, in the period between the second half of April and mid-June.

Monitoring of numbers and activity of mammalian predators (American Minks, Foxes, Raccoon Dogs) was carried out in two ways: as a separate task consisting in tracking the animals 2-3 times in winter and early spring throughout the entire part of the river under active protection and, "on the occasion" during the work in bird colonies in the spring and summer.

In addition to active protection measures, information and promotion activities were carried out. The basic information medium with a national reach is the Project Website (10,580 visits to the website).

In line with the assumptions of the Communication Plan, four main information events were implemented:

1. a press article (in “Ptaki Polski”, circulation 4,000 copies)
2. a radio broadcast (“Radio Warszawa”, audience approx. 9,300 people)
3. a Nature Seminar opening the project (81 people)
4. a conference closing the Project (114 people)

and three information support activities:

1. 1. informational and promotional meetings with school and university youth (5 meetings in total, 174 participants)
   2. a 12-board wall calendar for 2025 (1,500 copies)
   3. Project board placed on the building of the field station in Wróble

The main beneficiaries of the project are primarily birds breeding on islands in the middle Vistula riverbed. Without the implementation of the proposed active protective measures, in the perspective of a decade, the middle Vistula River will be impoverished by at least one species (Mew Gull), and two other - Common Tern and Little Tern are likely to experience a further, then probably drastic decline in numbers; The second beneficiary of the project will be the bodies responsible for managing the Natura 2000 SPA Dolina Wisły Środkowej PLB140004, which are the Regional Directors for Environmental Protection in Warsaw and Lublin. The proposed protection measures are consistent with the approved Plans of Protection Tasks for this Natura 2000 area. All private and public entities (including universities, scientific institutes, Polish Academy of Sciences) and nongovernmental organizations working for nature protection (including OTOP, PTOP, MŚTO, WWF Poland, Greenmind, Salamandra, Coalition Save Rivers, etc.), that can implement the proposed protective measures in other areas inhabited by Charadriiformes or other bird species for which the proposed actions will be adequate to their needs will benefit. A good example is the Nature Society “Bocian”, which first implemented some of our original protective measures (placing dummy eggs in nests) in the project "Protection of the Eurasian Curlew in the key refuges of the species in Poland" and later recommended them as one of several in the National Protection Plan for this species (Wierzbicka 2014, Lewtak et al. 2016).

Active conservation measures carried out as part of the project allowed for:

1. 1. Reduction of the American mink population in the middle Vistula riverbed by over 20 individuals;
   2. Reduction of the red fox population in the middle Vistula valley by over 60 individuals;
   3. Protection of bird breeding grounds using a system of electric fences and protection of bird eggs using incubators and dummy eggs allowed for a significant increase in the hatching success and the breeding success of no less than 100 pairs of Common and Black-headed Gulls, 50 pairs of Common Terns and Little Terns, and a dozen or so pairs of Oystercatchers and several pairs of Mediterranean Gulls (in the case of the latter two species - all that nested annually in this part of the river);
   4. Environmental monitoring and the exchange of Common Gull eggs between spatially separated aggregations of nests of this species allowed to control and strengthen the genetic diversity of the Vistula population

Information and promotional activities made it possible to reach a very wide and diverse group of recipients with information on threats to the Vistula avifauna, methods and forms of active protection of bird species experiencing a drastic decline and the key role of the EEA funds in ensuring financing of these pro-nature activities:

1. 1. 1. The Project Website had 10,580 hits;
      2. The press article in the “Ptaki Polski” had a circulation of 4,000 copies;
      3. The radio broadcast on “Radio Warszawa” had a listenership of approx. 9,300 people;
      4. The Nature Seminar opening the project was attended by 81 people;
      5. The Conference closing the project was attended by 114 people;
      6. A total of 174 participants participated in informational and promotional meetings with school and university youth (5 meetings);
      7. The 12-sheet wall calendar for 2025 was received by 1,500 people.