The Impact of a Catastrophic Flood on Species and Size Composition of The

Acta Oecologica 108 (2020) 103608

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Acta Oecologica

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The impact of a catastrophic flood on species and size composition of the T diet of fish-eating birds ∗ Alena Hadravováa, , Pavel Čechb, Martin Čecha,c a Institute for Environmental Studies, Faculty of Science, Charles University, Benátská 2, 128 01, Prague, Czech Republic b Czech Union for Nature Conservation, 02/19 ZO ČSOP Alcedo, Blanická 1299, 258 01, Vlašim, Czech Republic c Biology Centre of the Czech Academy of Sciences, Institute of Hydrobiology, Na Sádkách 7, 370 05, České Budějovice, Czech Republic

ARTICLE INFO ABSTRACT

Keywords: Floods in June 2013 affected significant portions of the Czech Republic (total damages amounted ~600 millions Common kingfisher (Alcedo atthis) of euro). This study examines the impact of catastrophic flood on the species composition and size of fish prey in Diagnostic bones the diet of the common kingfisher (Alcedo atthis), a fish-eating bird, nesting and hunting on Botič stream (Prague, Diet composition Czech Republic) in 2013. Hundred and forty years water (flow 74.5 3m s−1) caused considerable damage to Regurgitated pellets property and it is likely that the character and size composition of biota, especially fish, changed. This should be Nesting sediment reflected naturally in the diet of resident kingfishers. The diet of kingfishers before and after the flood were Floods investigated from the mass of regurgitated pellets, which were collected from the nest tunnel and chamber immediately after the successful breeding period before and after the flood event. Before the flood (normal 3 −1 situation; flow 0.4–1.5 m s ), the average length of fish caught was 6.5 cm LT (total length), average weight

2.6 g, and the index of food diversity was 1.58. After the flood, the average length of fish caught was 7.5 cmL T, weight 4.1 g, and the index of the food diversity was 1.36. It was evident that after the flood kingfishers were forced to hunt significantly larger prey. Six fish species (Gobio gobio, Squalius cephalus, Perca fluviatilis, Scardinius erythrophthalmus, Rutilus rutilus, Pseudorasbora parva) which were hunted both before and after the flood com posed 96.5 and 99.8% of the catch (by numbers). Surprisingly, the impact of floods may not always be reflected in the species composition of the diet of fish-eating birds, it mostly depends on the presence of fish broadly occurring in the stream, natural stability of the fish stock and on the composition of the fish assemblage in the upstream catchment area.

1. Introduction diversity and distribution of aquatic organisms, particularly fish (Čech and Čech, 2004; Čech et al., 2007). Such changes could then be re Floods are extreme hydrological events, which are usually short flected even in the diet of fish-eating predators (diet composition, term and sharply delineated (Lake, 2000). Their impacts are reflected in hunting success etc.; Luz-Agostinho et al., 2008; Čech and Čech, 2011, both natural and urban environments. They have effects on both the 2013). abiotic and biotic components of streams, rivers and reservoirs (Lake, Čech and Vejřík (2011) have shown the impact of the flood on the 2000; Čech et al., 2007; Lugeri et al., 2010). Floods have a pre hunting success of great cormorant (Phalacrocorax carbo). During the dominantly negative impact on organisms, primarily lead to a decline in high flow, some individuals were not able to hunt, some hunted but body condition (Reiley et al., 2017), fecundity, species richness (Chiu failed to catch the amount of fish corresponding to their daily dose. et al., 2013), and may lead to a population decline (Jurajda et al., 2006; Similarly, Prigioni et al. (2006) have shown the impact of floods on the Kubín et al., 2018; Maxwell et al., 2018). They can change habitat hunting success of Eurasian otter (Lutra lutra). Even in this fish-eating availability and structure (Breck et al., 2003; Wilson and Peach, 2006; predator, the increasing water turbidity and water flow significantly Yamanakaa et al., 2019) and cause changes of ecosystem processes reduced the ability to catch a fish. Otters and cormorants pursue their (Reich and Lake, 2015). Fast-flowing flood water has a strong potential prey underwater and although they are predominantly visual predators, to create material (Romanescu and Nistor, 2011) and nutrient losses they also use tactile cues (Prigioni et al., 2006; Grémillet et al., 2012). (Pecqueur et al., 2011). Floods cause significant changes to the In contrast, the common kingfisher (Alcedo atthis) uses diving/

∗ Corresponding author. E-mail addresses: [email protected] (A. Hadravová), [email protected] (P. Čech), [email protected] (M. Čech). https://doi.org/10.1016/j.actao.2020.103608 Received 19 January 2020; Received in revised form 3 June 2020; Accepted 15 June 2020 1146-609X/ © 2020 Elsevier Masson SAS. All rights reserved. A. Hadravová, et al. Acta Oecologica 108 (2020) 103608

floods in 2002, that affected the entire territory of the Czech Republic (only 20 × higher flow in a particular stream; at some middle sized and large rivers, however, a thousand years flood estimated; total damages in the country amounted to 3 billions of euros). The floods had an effect on species composition in the diet of kingfisher: fewer fish species and different fish species were found in the sample collected after the cat astrophic flash flood in 2001. The floods in 2002 were much less de vastating to the aquatic biota of that particular stream and, on the contrary, led to an increase in the number of species in the diet of kingfishers compared to the normal situation (at that time Štěpánovský stream served as a refuge for fish, they migrated into the stream from the heavily swollen, larger Sázava River; Čech and Čech, 2004, 2011). Kingfisher (Fig. 1) has limited digestion abilities. It means that only the soft tissues can be digested from the caught prey, and the residues – bones, scales, eye lenses etc. - are regurgitated in a form of a compact pellet (Cramp, 1990; Reynolds and Hinge, 1996; Čech and Čech, 2011, 2015). During the breeding period, the mass of regurgitated pellets Fig. 1. Female (right) and male (left) of common kingfisher (Alcedo atthis) at forms nesting sediment, which is located in the nest chamber of the Botič stream (Prague, Czech Republic). Photo: A. Hadravová. kingfisher. From the analysis of regurgitate pellets, one can gain qua litative and quantitative information about the diet of the kingfisher (Vilches et al., 2012; Čech and Čech, 2015, Čech and Čech, 2017a; Novčić and Simonović, 2018) and subsequently reconstruct even the harpooning to catch the prey (i.e. exclusively a visual predator). This impact of floods on the local ichthyofauna (Čech and Čech, 2011, bird identifies fish or aquatic invertebrates based on their movement 2013). and shape, when sitting on a low perch or when hovering above the The aim of the present study is to focus on the qualitative and water (Cramp, 1990; Čech and Čech, 2011; Vilches et al., 2013b). quantitative parameters of the diet of a kingfisher from the nesting site The kingfisher hunts fish from the entire water collum(Hallet, on Botič stream (Prague, Czech Republic) during a normal situation and 1977; Reynolds and Hinge, 1996; Campos et al., 2000; Čech and Čech, after the catastrophic flash flood in June 2013. This study represents 2011, 2013; Vilches et al., 2013a). During the normal river/stream si the first, unique observation of the impact of a drastic natural event on tuation, the diet of kingfishers is composed of either benthic species like the diet composition of a fish-eating predator during one breeding gudgeon (Gobio gobio) or bullhead (Cottus gobio), sub-surface species season at one single stream (identical nesting locality, occupied by one like European chub (Squalius cephalus) or bleak (Alburnus alburnus), or pair of kingfishers). The main questions were: 1) Does the food diversity mid-water species (occurring mostly in the middle of the water column) index changed after the catastrophic flood? 2) Does the size of fish like European perch (Perca fluviatilis), roach (Rutilus rutilus) or stone caught by a kingfisher differ before (normal situation) and after the moroko (Pseudorasbora parva) (Čech and Čech, 2013, Čech and Čech, catastrohic flood? It is hypothesized that the catastrophic flood will 2017a). At most sites, a kingfisher prefers cyprinid species (Cyprinidae; have crucial effect on the size/weight of hunted fish (larger after the Raven, 1986; Vilches et al., 2012; Čech and Čech, 2015; Novčić and flood; the smallest fish washed out from the system) as well as the effect Simonović, 2018). It chooses its prey by size (Hallet, 1977; Reynolds on the broadness of the diet spectrum (wider after the flood; newly and Hinge, 1996; Čech and Čech, 2013, 2015) and body shape (Cramp, established “Monte Carlo” community from resident fish and fish ori 1990), particularly prefering slender fish (Zając and Dobrowolska, ginating from the catchment area lacking any very dominant species to

2007; Čech and Čech, 2011). Kingfishers hunt fish ranging in size (LT, focus on). total length) from 1.5 to 12 cm (Čech and Čech, 2011, 2015). These small fish are more theatened by floods than fish of larger sizes 2. Methods (Schlosser, 1985; Cattanéo et al., 2001; Freeman et al., 2001; Jurajda et al., 2006) – they are washed out, which should be immediately re 2.1. Study area and the catastrophic flood event flected in the diet of kingfishers. In the former study, Bunzel and Drüke (1989) have found that the The study was carried out on the Botič stream in the Czech Republic. kingfisher was unable to hunt during the flood. In contrast, Čech and It is a part of the lower basin of the Vltava River (coordinates of the Čech (2013) have shown that the kingfisher was not starving during the tributary with the Vltava: 50°04ʹ01ʺ N, 14°24ʹ53ʺ E, 188 m a. s. l.), and long-lasting flood event. In this study, kingfisher hunted larger and flows through the capital city of Prague and Central Bohemia. The heavier prey during the long-lasting flood event compared to the length of the stream is 34.5 km (21 km of which is situated in Prague). normal situation and similarly, sub-surface fish species were more The catchment area is 135.8 km2 and an average annual flow is hunted during the long-lasting flood compared to the normal situation 0.44 m3 s−1. The canopy of this naturally meandering lowland stream is in which, in contrast, the benthic species composed the gross majority composed of black alder (Alnus glutinosa), crack willow (Salix fragillis), of the diet. Same authors have demonstrated that floods on the Štěpá white willow (S. alba), European ash (Fraxinus excelsior), common novský stream (Central Bohemia, Czech Republic) in 2001 and 2002 aspen (Populus tremula) and black elder (Sambucus nigra) (Vlček et al., affected the species composition of the diet of kingfisher (Čech and 1984; Rojková and Sláma, 2013). Čech, 2011). The authors compared the nesting sediments from 3 per The floods in June 2013 affected a significant part of theCzech iods – a normal situation before the floods, after the catastrophic flash Republic (total damages amounted to 600 million euros). The streams flood in 2001 (more than 500 × higher flow) and one year after the across the Vltava River, in a part of the Elbe River, and marginally in

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sediment; Čech and Čech, 2015) collected from the nest tunnel and the chamber before (30 May 2013; 5 chicks; 390 ml of regurgitated mate rial) and after (16 August 2013; 6 chicks; 465 ml of regurgitated ma terial) the catastrophic flood on the Botič stream in early June 2013. The mass of regurgitated pellets was collected immediately after the end of each breeding period (when the chicks had left the nest), which sampling design was in full conformity with the work of other authors (cf. Hallet, 1977; Raven, 1986; Reynolds and Hinge, 1996; Vilches et al., 2012, Vilches et al., 2013a, 2019, etc.). The regurgitated material originated from the nesting site located c. 3 km under the Hostivař Reservoir in the Botič Meandres Natural Reserve (50°03ʹ02ʺ N, 14°30ʹ40ʺ E, 224 m a. s. l.), the most valuable part of the Prague natural park Hostivař – Záběhlice. The regurgitated materials were immersed in a concentrated de tergent solution for the period of one week, then washed through a sieve (mesh size 1 mm), and finally dried at room temperature. The mass of regurgitated pellets was analyzed under a binocular microscope (magnification 8 times and 16 times; Reynolds and Hinge, 1996; Čech and Čech, 2011, 2015). The regurgitated material collected before and after the flood was analyzed separately (i.e. all diet remains from each successful breeding period; one nest prior and one nest after the cata strophic flood event). To identify the species and sizes (total length –L T, weight – W) of the fish preyed upon, pharyngeal bones (ossa pharyngea) were used for cyprinid (Cyprinidae) and balitorid (Balitoridae) species and preopercual bones (praeoperculare) for percid (Percidae) species (Reynolds and Hinge, 1996; Čech et al., 2008; Čech and Vejřík, 2011; Čech and Čech, 2013, Čech and Čech, 2017a). In total, 2143 of those diagnostic bones (from ca. 570 pellets) were examined in the study. The measurements selected were the pharyngeal bone tip for cyprinid spe cies and the preopercular gap for percid species (for details see Čech et al., 2008; Čech and Vejřík, 2011). The size of diagnostic bones was measured with 0.1 mm precision and converted to total length of the fish using a species specific linear regression equation provided byČech et al. (2008), Čech and Vejřík (2011), Čech and Čech (2013, Čech and Fig. 2. Comparison of the water level of the Botič stream under the dam of the Čech, 2017a. In the case of one stone loach (Barbatula barbatula) the Hostivař Reservoir (concrete outlet basin and outlet channel) during (a) normal 3 −1 linear regression equation of pharyngeal shank predicting total length spring situation (flow 0.44 m s ) and during (b) the catastrophic flood in was taken from the work of Reynolds and Hinge (1996). The weight of early June 2013 (flow 74.5 m3 s−1). Photo: A. Hadravová (a), M. Čech (b). individual fish was calculated from their total lengths using species specific equations provided by Čech and Čech, 2017a. the Thaya River basins got swollen. After heavy rains in the Vltava River basin on 1 and 2 June 2013 (precipitation up to 94 mm per 24 h; average precipitation amount for the whole June within the years 2.3. Statistical analysis 1961–2010 ca. 72 mm; Czech Hydrometeorological Institute, unpubl. data) the flow of the Botič stream under the Hostivař Reservoir reached The data were tested using Chi-square test (period dependent - be the extreme level of a hundred and forty years water (flow 74.5 m3 s−1; fore and after the catastrophic flood event – contribution of individual according to the Prague municipal bureau flood plan for Botič, the state fish species to the diet of kingfisher), and Kruskal-Wallis test (size/ of danger is on the flow level of 35 m3 s−1; Fig. 2). The effect of the weight of fish preyed upon by the kingfisher before and after the cat flood on the stream was amplified by an unexpected mass release of astrophic flood event). The size/weight prey data were further com water from the Hostivař Reservoir (human fault). The flood caused pared with the results from other streams, rivers and reservoirs in considerable damage to property, which amounted to nearly 150 mil Central Europe, where the diet of kingfishers was previously analyzed lion euros in Prague (Sandev et al., 2013). It is likely that the cata and which correspond to either normal situation (30 nests) or the si strophic flash flood on the Botič stream also changed the character and tuation immediatley after the catastrophic flood in June 2013 (one nest size composition of the biota. This change should be reflected in the diet – Blanice River, Vltava River basin, 47 km south-east from the locality of the kingfisher, which nests and hunts there. at Botič stream; Čech and Čech, 2015, Čech and Čech, 2017a; M. Čech, P. Čech, unpublished data). The data were processed using the Rx64 3.1.2 statistical software (R Core Team, 2017). 2.2. Sampling The food diversity index of the kingfisher was calculated as a Shannon's diversity index. For comparison of the number of species The species composition and size of fish prey in the diet of the preyed upon by the kingfisher (before and after the flood) we calculated kingfishers were investigated from the mass of regurgitated pellets (nest the Sørensen similarity index (Sørensen, 1948). This index was used

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Table 1 Fish species composition in the diet of common kingfisher (Alcedo atthis) hunting on the Botič stream before and after the catastrophic flood in June 2013.

Botič stream

Species Before the flood After the flood

n %a LT (cm) W (g) %w n %a LT (cm) W (g) %w Average (min, Average (min, Total Average (min, Average (min, Total max) max) max) max)

Roach Rutilus rutilus 41 6.0 7.1 (2.2, 9.1) 3.5 (0.1, 6.7) 143.0 8.1 64 12.5 8.1 (5.76, 10.9) 5.1 (1.7, 11.3) 328.5 15.8 Bleak Alburnus alburnus 19 2.8 7.6 (6.1, 8.9) 3.5 (0.1, 6.7) 43.7 2.5 ─ ─ ─ ─ ─ ─ Stone moroko Pseudorasbora parva 24 3.5 6.1 (4.1, 7.6) 1.5 (0.5, 2.6) 36.2 2.0 7 1.4 5.1 (2.1, 7.9) 1.3 (0.1, 2.8) 9.1 0.4 Gudgeon Gobio gobio 335 48.6 6.9 (4.5, 10.3) 2.9 (0.7, 8.7) 962.1 54.2 274 53.6 8.0 (2.1, 11.7) 4.4 (0.1, 3.0) 1217.6 58.5 White bream Abramis bjoerkna 2 0.3 8.1 (7.8, 8.4) 5.5 (4.9, 6.2) 11.1 0.6 ─ ─ ─ ─ ─ ─ Prussian carp Carassius auratus ─ ─ ─ ─ ─ ─ 1 0.2 6.3 (6.3, 6.3) 3.7 (3.7, 3.7) 3.7 0.2 European chub Squalius cephalus 106 15.4 6.0 (1.4, 9.4) 2.4 (0.02, 8.0) 251.7 14.2 34 6.7 7.1 (2.7, 9.9) 3.9 (0.2, 9.4) 131.1 6.3 Rudd Scardinius erythrophthalmus 70 10.2 7.0 (4.9, 8.7) 3.4 (1.1, 6.3) 237.4 13.4 46 9.0 7.8 (3.3, 9.4) 4.9 (0.3, 8.2) 225.1 10.8 Tench Tinca tinca 6 0.9 4.6 (3.6, 5.2) 1.4 (0.6, 1.9) 8.1 0.5 ─ ─ ─ ─ ─ ─ Stone loach Barbatula barbatula 1 0.2 3.1 (3.1, 3.1) 0.2 (0.2, 0.2) 0.2 0.01 ─ ─ ─ ─ ─ ─ European perch Perca fluviatilis 85 12.3 4.6 (3.6, 8.0) 1.0 (0.4, 5.5) 83.5 4.7 85 16.6 5.8 (4.5, 7.3) 2.0 (0.8, 3.9) 166.6 8.0 Total 689 100 1776.8 100 511 100 2081.7 100 Food diversity index 1.58 1.36 Similarity index 0.71 n - number of individuals; %a - percentage of abundance; LT - total length (cm) of fish individual; W (g) - weight (g) of fish individual; Average (min, max) - average length (weight), minimal and maximal length (weight), Total - total weight (g) of all fish of appropriate species in the sample; %w - percentage of total weight"

also to compare species composition of the diet of the kingfisher on the Kingfishers on the Botič stream before the catastrophic floodin Botič stream to that on other streams and rivers in the same region 2013 hunted fish ranging from 1.4 to 10.3 cm LT (average 6.5 cm, (data from Čech and Čech, 2011, 2013, 2015, Čech and Čech, 2017a) to median 6.4 cm; Table 1, Fig. 3a) and from 0.02 to 8.7 g in individual evaluate within stream and between stream species similarity weight (average 2.6 g, median 2.1 g; Table 1, Fig. 3b). This corresponds (Appendix 1). to the normal situation on other streams, rivers and reservoirs in Cen tral Europe (average size 6.6 cm, median 6.8 cm, average weight 3.0 g, 3. Results median 2.5 g; n = 17,815; Fig. 3). After the catastrophic flood, king

fishers hunted fish ranging from 1.2 to 11.7 cmLT (average 7.5 cm, Before the catastrophic flood on the Botič stream in June 2013, 689 median 7.4 cm; Table 1, Fig. 3a) and from 0.1 to 13.0 g in individual fish of 10 species and 3 families (Cyprinidae, Percidae, Balitoridae) weight (average 4.1 g, median 3.4 g; Table 1, Fig. 3b). These values were identified in the diet of the kingfisher. Gudgeon, European chub, correspond well to the situation after the catastrophic flood in June European perch, rudd (Scardinius erythrophthalmus), roach and stone 2013 on the Blanice River (average size 7.8 cm, median 7.6 cm, average moroko represented 96.5% (numerically) of the diet. The most hunted weight 4.4 g, median 3.8 g; n = 703; Fig. 3). fish species was gudgeon – 48.6%, followed by European chub – 15.4%, The size of fish in the diet of the kingfishers hunting on Botič stream European perch – 12.3%, and rudd – 10.2%. The food diversity index after the catastrophic flood was significantly larger than the size of fish was 1.58 (Table 1). before the flood (Kruskal-Wallis test; H1,1200 = 119.02, P < 0.0001, After the catastrophic flood on the Botič stream in June 2013, 511 Table 1, Fig. 3a). Similarly, fish preyed upon after the flood were sig fish of 7 species and 2 families (Cyprinidae, Percidae) were identified in nificantly heavier compared to fish hunted before the flood (Kruskal- the diet of the kingfisher. Gudgeon, European chub, European perch, Wallis test; H1,1200 = 139.62, P < 0.0001, Table 1, Fig. 3b). rudd, roach and stone moroko represented 99.8% of the diet. The most hunted fish species was gudgeon – 53.6%, followed by European perch 4. Discussion – 16.6%, roach – 12.5%, and rudd – 9%. The food diversity index was 1.36 (Table 1). The catastrophic flood on the Botič stream in 2013 had an impact on Six fish species (gudgeon, European chub, European perch, rudd, the size (high) and species composition (low) in the diet of the common roach and stone moroko) were hunted both before and after the flood. kingfisher, but most likely did not cause any starvation of the fish- Bleak, tench (Tinca tinca), white bream (Abramis bjoerkna), and stone eating predator, which fact was reflected in its ability to resettle the loach were hunted only before the flood (n = 28). Accidental catch of locality and to breed there successfully immediately after this extreme, Prussian carp (Carassius auratus) was recorded only after the flood natural event. Even during the long-lasting flood on the Blanice River in (n = 1; Table 1). The contribution of individual fish species to the diet 2009 (Čech and Čech, 2013) and after the floods on the Štěpánovský of kingfisher differed significantly prior and after the catastrophic flood stream in 2001 and 2002, the kingfisher did not starve (Čech and Čech, 2 event (χ0.95,5 = 43.72, P < 0.0001). The Sørensen similarity index 2004, 2011) and was able to breed successfully at these watercourses. (comparing fish species similarity in the diet of kingfisher before and Also in the case of Swainson's warblers (Limnothlypis swainsonii), the after the flood) was, however, 0.71 (i.e. relatively high;Table 1 and cf. occurrence of which is bounded to hardwood floodplain forests and with Appendix 1). which feed on arthropods in terrestrial dead leaf litter, the species did

4 A. Hadravová, et al. Acta Oecologica 108 (2020) 103608

free-flowing Yampa River in northwestern Colorado even benefited from the flood because spilled water from the riverbed provided him an easy access to many more trees (Breck et al., 2003). In contrast, in the case of the great cormorant, it has been shown that during the flood some individuals were not able to catch a fish, others hunted only a small amount of prey which, however, did not correspond to their daily dose (Čech and Vejřík, 2011). Similarly, Prigioni et al. (2006) found that the Eurasian otter decreased its ability to catch a fish during the flood. In the case of bearded tit (Panurus biarmicus), whose main food source in winter is the seeds of reeds and other aquatic plants, winter floods are the cause of loses of their habitat and of food deficiency (Wilson and Peach, 2006). From the examples above, it is evident that floods have curiously variable effects on the feeding ecology of animals ranging from severe to moderate disadvantage to obvious advantage. The flood on the Botič stream had not such a drastic impact on the species composition of the diet of kingfishers as in the case of an even more extreme, flash flood on the Štěpánovský stream in 2001 (500 × higher water flow; the water masses even replaced the former bottom substrate, comprised of boulders and sand, by clay and mud). While prior this flood, the diet of kingfisher was dominated by brown trout (Salmo trutta m. fario), brook trout (Salvelinus fontinalis) and bullhead (altogether 56.5% of prey by numbers) after that catastrophic event these fish composed only a negligible part of the catch (0.2–11.4%; Čech and Čech, 2004, 2011). In the case of the Botič stream, the six most numerous species (gudgeon, European chub, Eur opean perch, rudd, roach and stone moroko) were found in the sample both before and after the flood. These fish composed 96.5 and 99.8% of the diet respectively, i.e. the species spectrum of fish hunted by a kingfisher before and after the flood was apparently similar. This cor responds to a similar finding from Blanice River (cf.Appendix 1). In an agreement with the present study, Jurajda et al. (2010) found that after the extreme hundred-year floods on the lowland Morava River the species diversity of small sized fish remained similar to other years. It is likely that the difference in the situation on Botič stream/ Blanice River and Štěpánovský stream is in the status and character of individual watercourses. Štěpánovský stream is a small trout fishery, however, with a number of non-trout ponds and trout unsuitable stretches in the upper reaches. These conditions make the stream a fragil system succesible to any disturbances. Most probably, during the catastrophic, flash flood in 2001 the local ichthyofauna was washed out and cyprinids from upper reaches colonized the stream. Subsequently, this fact was mirrored in the diet of kingfisher (Čech and Čech, 2011). In contrast, both Botič stream and Blanice River are relatively large non-trout fisheries where coarse fishes (cyprinids predominantly) pre

Fig. 3. (a) Size (LT in cm; mean ± SD) and (b) weight (W in g; mean ± SD) of vailed in most of the basins. Moreover, the presence and close proxi fish prey found in the diet of common kingfishers (Alcedo atthis) hunting on the mity of the Hostivař Reservoir (Botič) has a significant effect on the Botič stream before the catastrophic flood (n = 689; normal situation) and after species composition and the natural stability of the fish stock in the the catastrophic flood (n = 511) in June 2013 and comparison with the general watercourse (Humpl and Pivnička, 2006). It is again likely that even in situation on streams, rivers, and reservoirs in Central Europe (n = 17,815; Čech the case of Botič stream and Blanice River the local ichthyofauna was at and Čech, 2015, Čech and Čech, 2017a) and the situation on the Blanice River least partialy washed out by the extreme flood water but it was im after the similar, severe flood in June 2013 (n = 703;Čech and Čech, 2015; M. mediately replaced by the same species from the upstream catchment Čech and P. Čech, unpublished data). The circles and the triangles indicate the area. Subsequently, this fact was recorded in the diet of the resident average, the whiskers indicate ± SD. fish-eating predator (this study). The size of fish in the diet of the kingfisher hunting on Botič stream after the catastrophic flood was significantly larger than the size of fish not suffer from deficiency of the diet after the floods on Mississippi before the flood (difference of 1.0 cmL T and 1.5 g). This corresponds to River, Midwestern USA (Reiley et al., 2017). The North American the results from Blanice River which was affected by the same hydro beaver (Castor canadensis) on the flow-regulated Green River and the logical event in the same period of the year 2013 (cf. Fig. 3). Similarly,

5 A. Hadravová, et al. Acta Oecologica 108 (2020) 103608 during the long-lasting flood event on the Blanice River in 2009 king 2017a). However, in the case of providing the food to small chicks fishers caught significantly larger fish prey compared to the normal younger than ca. 10 days, the hunting of larger fish has to be even risky. situation (Čech and Čech, 2013). There is an apparent danger of chick suffocation when the oversized There is an apparent time shift between the first (prior the flood) prey get stuck in the oesophagus. Alternatively, these young chicks are and the second (after the flood) diet sample analyzed for the purpose of not even strong enough to be able to hold the large and heavy prey in the present study representing mid-spring and mid-summer kingfisher the beak and to try to swallow it. Then the provided fish are cumulating breeding periods on the Botič stream. Considering this time shift, it on the edge of the nest chamber, chicks are starving and all the effort of could be argued that the observed increase of prey size in the diet of parental birds is wasted (Čech and Čech, 2017). kingfisher could be simply a result of an ongoing season (not a result of a catastrophic flood) since within the period of over two months the 5. Conclusion young-of-the year (YOY) fish could grow up significantly. However, this is not the case of this study since in May, in conditions of the Czech According to a number of researches, extreme events, like droughts, Republic, these newly hatched fish are either two small or they are still fires, hurricanes and intense rainfall leading to catastrophic floods, will not in the system at all (Čech et al., 2005; Jůza et al., 2010; Kratochvíl be expected to occur more and more frequently in the following years et al., 2010). (Easterling et al., 2000; Romanescu and Stoleriu, 2013). However, it In altitudes similar to Botič stream, the first spawners of the year are seems that even if floods will be more frequent and even if they will species like northern pike (Esox lucius; in early March) or asp (Leuciscus change the conditions for fish hunting (higher and turbid water, fast aspius; in March/April) (Hladík and Kubečka, 2003; Šmejkal et al., flow, fish replacement, etc.), in many cases they will not have a crucial 2017). Both species were, however, not present in the diet of kingfisher effect on the diet of common kingfisher since the bird is an opportu on this particular stream (this study). The spawning of other early nistic predator (Čech and Čech, 2013; Vilches et al., 2019; this study). spawners like European perch, roach or European chub take place from In case of catastrophic floods coming during the breeding season (af mid-April to mid-May (Hladík and Kubečka, 2003; Čech et al., 2012). fecting the success of individual breeding periods), the main problem These newly hatched fish are, however, too small (usually much less for the local kingfisher populations seems to be a possibility of chick than 2 cm L ) to be a relevant prey of kingfisher till the end of May T drowning in the nest chamber and also a nest wall/site destruction (Čech et al., 2005; Jůza et al., 2010; Kratochvíl et al., 2010). In the diet (Bunzel and Drüke, 1989; Čech and Čech, 2017). sample collected before the catastrophic flood only one European chub was smaller than 2 cm LT and only two other fish (roach) were under the size of 3 cm LT (this study). This illustrates the fact that in spring, Author contributions during the first nesting of the year, kingfishers are forced to strictly focus on fish hatched in the previous year (or even older fish, e.g. in the Alena Hadravová: Formal analysis, Investigation, Writing – Original cases of gudgeon or stone loach). In contrast, the YOY fish of an ap draft, Visualization. Pavel Čech: Conceptualization, Methodology, propriate size (3–9 cm LT; Čech and Čech, 2015) are well in the system Martin Čech: Conceptualization, Methodology, Validation, Writing – in summer (Kratochvíl et al., 2012). Considering this, during the per Original draft, Visualization. sisting normal river/stream situation the size of fish hunted by king fishers should be expected even in the opposite way, with larger fish in Declaration of competing interest the diet in spring (fish older than YOY) and smaller or similar sized fish in summer (YOY and older fish together). The authors declare that they have no known competing financial On the Botič stream, the pre-flood prey size well resembles a interests or personal relationships that could have appeared to influ common diet of kingfishers in Central Europe during the normal ence the work reported in this paper. stream/river conditions (cf. Fig. 3). Then, it is likely that the cata strophic flood washed out small, newly hatched fish from the system as also described by Čech et al. (2007). In the subsequent breeding period Acknowledgements (after the flood), kingfishers were forced to hunt larger fish remaining in the stream or fish which originated from the upstream parts of the The authors thank M. Morris for carefully reading and correcting the Botič stream basin including Hostivař Reservoir which were shifted English and E. Mori for helpful comments to the manuscript. The study downstream by the flood water. It should be noticed that such a size was supported by the Czech Academy of Sciences within the program of dependent wash out effect may not always be applied. For Alpine the Strategy AV 21 (project No. VP21 – Rescue and Renewal of bullhead (Cottus poecilopus) in the streams of the Carpathian Mountains, Landscape) and the Czech Union for Nature Conservation (Biodiversity Czech Republic, Kubín et al. (2018) have shown that the largest in Conservation project). The permission for any intervention to the dividuals were washed out by the flash flood while smaller fish re biology of kingfisher (strongly endangered species in the Czech mained at the study places. Republic according to the act No. 114/1992 and regulation No. 395/ The benefit of hunting larger fish (i.e. larger than the optimum size 1992) was granted by the Ministry of the Environment of the Czech of ca. 6.0–8.0 cm LT; Čech and Čech, 2015) is rather controversial. It has Republic. The study is part of a long-term ALCEDO project of the Czech been shown that parents feed their youngs with as big fish as these are Union for Nature Conservation (running from 1994) focusing on the able to swallow (safely) to optimize their foraging behaviour and biology and conservation of kingfishers (the second author is the head maximize the breeding success (Čech and Čech, 2011, Čech and Čech, and coordinator of the project for the Czech Republic).

6 A. Hadravová, et al. et Hadravová, A. Appendix 1. Similarity index (S; Sørensen, 1948) for comparison of species composition in the diet of the common kingfisher (Alcedo atthis) on the Botič stream to that on the Blanice River, Chotýšanka, Martinický, Losinský, Křešický, Trnava, Řečický and Štěpánovský streams and comparison of species composition before and after the flood on the Blanice River in 2013 and before and after the floods on the Štěpánovský stream in 2001 and 2002. Data from the work of Čech and Čech (2004, 2011, 2013, 2015, 2017a and unpubl. data)

Species Botič stream Blanice River Blanice Chotýšanka Martinický Losinský Křešický Trnava Řečický Štěpánovský Štěpánovský Štěpánovský stream Štěpánovský (pooled (pooled data) River stream (pooled stream n = stream n stream stream n stream n stream (pooled stream – before – after the flood in stream – 1 year data) n = 2 n = 9 – after data) n = 4 1 = 1 (pooled data) = 1 = 1 data) n = 3 the floods n = 1 2001 n = 1 after the floods in the flood n = 2 2002 in 2013 n = 1 n = 1

Gudgeon Gobio gobio ● ● ● ● ● ● ● ● ● ● ● ● ● European chub Squalius cephalus ● ● ● ● ● ● ● ● ● ● ● ● ● Roach Rutilus rutilus ● ● ● ● ● ● ● ● ● ● ● ● ● Bleak Alburnus alburnus ● ● ● ● ● ● ● ● ● ● ─ ● ● Stone moroko Pseudorasbora par ● ● ─ ● ─ ● ● ● ● ● ─ ● ● va Common dace Leuciscus leuciscus ─ ● ● ● ● ● ● ● ● ● ● ● ● Asp Aspius aspius ─ ● ● ─ ● ● ● ● ● ● ─ ─ ● Barbel Barbus barbus ─ ● ─ ─ ─ ● ● ─ ─ ● ─ ● ● Common bream Abramis brama ─ ● ─ ● ● ─ ● ─ ─ ─ ─ ─ ─ Tench Tinca tinca ● ● ─ ─ ─ ● ● ─ ─ ─ ─ ─ ─ Ide Leuciscus idus ─ ● ● ─ ─ ─ ─ ─ ─ ● ● ─ ─ Belica Leucaspius delineatus ─ ● ─ ─ ─ ─ ─ ─ ● ● ─ ─ ● Rudd Scardinius erythrophthalmus ● ● ● ─ ─ ● ─ ● ● ─ ─ ─ ─ Common carp Cyprinus carpio ─ ● ● ● ─ ─ ─ ─ ─ ● ─ ─ ● Nase Chondrostoma nasus ─ ● ─ ─ ─ ● ─ ─ ─ ● ─ ─ ● Vimba bream Vimba vimba ─ ─ ─ ─ ─ ● ─ ─ ─ ● ─ ─ ● 7 Prussian carp Carassius auratus ● ─ ─ ─ ─ ─ ─ ─ ● ─ ─ ─ ─ White bream Blicca bjoerkna ● ● ● ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ Stone loach Barbatula barbatula ● ● ● ● ● ● ● ● ─ ● ● ● ● Northern pike Esox lucius ─ ● ─ ─ ● ● ● ─ ● ● ● ─ ─ Brown trout Salmo trutta m. fario ─ ● ─ ● ● ● ● ● ● ● ● ─ ● Brook trout Salvelinus fontinalis ─ ─ ─ ─ ─ ─ ─ ─ ─ ● ● ─ ─ Grayling Thymallus thymallus ─ ─ ─ ─ ─ ─ ─ ● ● ─ ─ ─ ─ Bullhead Cottus gobio ─ ● ─ ● ● ● ● ● ● ● ● ● ● European perch Perca fluviatilis ● ● ● ● ● ● ● ● ● ● ● ─ ─ Ruffe Gymnocephalus cernuus ─ ─ ─ ─ ─ ─ ● ─ ● ─ ─ ─ ─ Zander Sander lucioperca ─ ● ─ ● ● ─ ─ ─ ─ ● ─ ● ─ Total 11 22 12 13 13 17 16 13 16 20 11 10 15 Similarity index (S) – Botič stre ─ 0.61 ─ 0.58 0.50 0.64 0.59 0.67 0.59 0.45 ─ ─ ─ am x other streams and rivers Similarity index (S) - before x a ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ 0.57 ─ fter the flood in 2001 (Štěp ánovský stream) Similarity index (S) – after the f ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ 0.72

lood in 2001 x after the flo Acta Oecologica108(2020)103608 ods in 2002 (Štěpánovský s tream) Similarity index (S) - before x a ─ ─ 0.65 ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ fter the flood in 2013 (Blan ice)

n - number of nest holes from which nesting sediment was collected; ● occurrence of the species in the nest sediment of the nest hole in the given locality; ─ species are not found in the locality A. Hadravová, et al. Acta Oecologica 108 (2020) 103608

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