Survey of biological status of Old-Drava has continued
The survey of the biological status of the Old-Drava brought new results in 2017. There are species and habitats of European significance in the oxbow and along it, which are traced regularly during the monitoring. These annual surveys give a unique and comprehensive picture of the Old-Drava, for which there was no opportunity before.
The most important habitats of the oxbow are aquatic plant communities and softwood gallery forests. These habitats are situated in an approximately 100-hectare area, which constitute one-third of the whole oxbow and its environment. The oxbow has several sections where the raising water level is expected to have a greater effect on riverside habitats. We have taken samples on these sections separately so that results regarding better water supply can be monitored with more accurate methods. The monitoring includes those species that are the most characteristic of the condition of the oxbow and the slowly flowing waters.
The most common natural habitats of the Old-Drava are riparian willow-poplar forests, which cover 72 hectare and that we monitored on three sampling sites. In these forests, besides several valuable tree species, the diversity of the undershrub is typically high, regarding that the stand consists of 30-40 species. During the observations in the spring the rare military orchid, narrow-leaved helleborine and white helleborine appeared. This reflects the outstanding natural values of the oxbow. None of the investigated gallery forest communities were characterised by considerable presence of alien species. Weeds, such as white helleborine (Cephalanthera damasonium), narrow-leaved helleborine (Cephalanthera longifolia) and military orchid (Orchis militaris) constituted 10% of the complete list.
Every month from the spring of 2017, surveys on the field have been done to get to know the dragonfly fauna better. Five sampling sites were marked out on the Old-Drava in a way that each typical part of the water is represented, so the survey gives a representative picture about the dragonfly fauna of the Old-Drava. Altogether, 23 dragonfly species were proven to occur on the Old-Drava in 2017, which is 35% of the species known in Hungary. On the sections with the most abundant number of species more than 600 individual were observed during the surveys. The observations prove that the biological state of the Old-Drava is excellent and especially favourable to dragonflies. The results also highlight that the composition of the dragonfly species can change year by year, and data of many years are needed to accurately survey the presence of the dragonflies.
The fish fauna of the river was examined twice on several sections. Sampling sites were marked out so that shores be as varied as possible to ensure that the results are sufficiently representative. During the two-day fieldwork in two different seasons, 953 fish were caught and defined altogether on 7 sampling sites. Out of the observed 22 species, 4 is protected and also considered as species of the Natura 2000 network list: the cactus roach (Rutilus virgo), the white-finned gudgeon (Romanogobio vladykovi), the European bitterling (Rhodeus amarus) and the Danubian spined loach (Cobitis elongatoides). It is of prominent significance of the natural values that the protected European bitterling (Rhodeus amarus) was found to be the third most common species (14,4%), but it is regrettable that there are two adventive fish as well, of which the pumpkinseed (Lepomis gibbosus) presented itself in the second largest number in the samples (14,7%). The most common fish species in the standing waters and streams was proven to be the roach (Rutilus rutilus), which constituted more than third of the catch. The stock of the rudd (Scardinius erythrophthalmus), which likes standing water, the common bleak (Alburnus alburnus), the silver bream (Blicca bjoerkna) and the Prussian carp (Carassius gibelio) also seemed to be stable. The Old-Drava in Barcs is favourable to fish that prefer standing water, or both standing water and streams at present. Fish that prefers flows occur only occasionally.
Amphibians and reptiles
During the survey in 2015 two years ago, the presence of altogether 8 amphibian species were proven, and in respect of the reptiles, only the sand lizard (Lacerta agilis) and the dice snake (Natrix tesselata) appeared. The results of the surveys clearly indicate that both the amphibian and reptile fauna is characterized by a low number of species and individuals. The reason for that is likely to be that there are a lot of terrestrial predators or omnivores (boar, fox, badger, otter) on the shore, and there is a significant number of pumpkinseeds (Lepomis gibbosus) and black bullhead catfish (Ameiurus melas) feeding on the eggs and spawns of amphibians in the Old-Drava. Surveys were continued by using variable sampling methods in March and April in 2017. Based on the results, we can keep saying that the presence of triton species cannot be excepted in the Old-Drava, but if they occur in the water, the number of individuals might be very low. During the far-reaching work in 2017 on the Old-Drava and its environment, individuals of other species were demonstrated or observed indirectly that had not appeared during former surveys. These include the common spadefoot (Pelobates fuscus), the European green toad (Bufo viridis), the European green lizard (Lacerta viridis) and the slowworm (Anguis fragilis). The results of the monitoring of 2017 also proved that the amphibian and reptile fauna of the Old-Drava is characterized by a low number of species and individuals.
The observation of birds has done twice in the spring, and data was recorded on more than 90 sites. Our primary aim was to assess the water-related species, that’s why we made the observations from a canoe. On the workday in late April, 302 individuals of 49 bird species were detected altogether, while in May 382 individuals of 43 bird species were observed. During these two observations the appearance of 60 bird species were proven on Old-Drava. There are 22 species among them that can be considered as water-related bird species. When evaluating the bird fauna from nature conservation point of view, we should highlight those species that are Natura 2000 species and appears on Old-Drava. The ferruginous duck (Aythya nyroca) is likely to be a potential nesting bird, as bird pairs are often seen in the middle of May. The presence of the little grebe (Tachybaptus ruficollis) is reckoned to 3 pairs in 2017, which is low concerning the habitat conditions. Among the common little bittern (Ixobrychus minutus) there were at least 2 nesting pairs in the area in 2017, but the number of pairs is certainly higher. The presence of the black-crowned night heron (Nycticorax nycticorax) and number of individuals that were observed presume a nest colony in the nearby. The purple heron (Ardea purpurea) is the most valuable bird in the area, ornithologists estimate that there were 7 pairs in 2017.
The complete report of the monitoring in Hungarian and the Croatian and English summary can be downloaded below.