En analyse af gylp fra hvid stork Ciconia ciconia i Danmark

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4 4 Sammenfatning Fødeindhold i gylp fra hvid stork Ciconia ciconia i Danmark 1976-2003 Naturhistorisk Museum i Aarhus, har undersøgt 362 gylp af hvid stork, indsamlet i perioden 1976-2003 af Hans Skov . Storkegylpene blev især indsamlet i det sydlige Jylland, i Himmerland og i Thy . De 362 gylp blev fragmenteret og analyseret for deres indhold af knogler fra hvirveldyr og børster fra regnorme, mens et udsnit bestående af 123 gylp også blev analyseret for rester af insekter og andre mindre organismer . Analyserne viste, at regnorme udgjorde en væsentlig del af de danske storkes fødegrundlag – på biomassegrundlag gennemsnitligt 77% af gylpene . Småpattedyr, især muldvarp og markmus, var relativt få i antal, men biomassemæssigt udgjorde de 16% af gylpene . Insekter, især større løbebiller og torbister, udgjorde ca . 7% . Padder, som anses for væsentlige fødeemner for storken, fandtes stort set ikke i gylpene, formentlig fordi deres bruskskelet opløses fuldkomment i storkens mave . På grund af den store tidsmæssige og rumlige fordeling af gylpene samt fraværet af padder i gylpene er det vanskeligt at konkludere noget sikkert om betydningen af ændringerne i det danske kulturlandskab i forhold til storkens uddøen i Danmark . Sammenlignes de herværende danske resultater med ældre danske oplysninger er det dog bemærkelsesværdigt, at de sidste danske storke har konsumeret betydeligt færre store insekter end tidligere, og at især regnorme udgjorde en meget højere andel . Udenlandske undersøgelser viser, at storke ofte spiser mange flere store byttedyr som mus, muldvarpe og padder, som de udenlandske habitater er rigere på end de danske . Det er derfor ikke usandsynligt, at ændringer i fødetilgængelighed er en medvirkende årsag til storkens forsvinden som dansk ynglefugl .
Summary Food contents in pellets of White Stork Ciconia ciconia in Denmark 1976-2003 Natural History Museum in Aarhus has investigated 362 pellets from Danish White Stork, collected during the period 1976-2003 by Hans Skov, especially from Southern Jutland (several locations), NW-Jutland (Vesløs, Vang) and NE- Jutland (Vegger) . All of the 362 pellets were fragmented and analyzed for the content of vertebrate bones, earthworm bristles, sand and pebbles, whereas a representative sample, consisting of 123 pellets from eight main locations, was further analyzed for remains of insects and other small organisms . The analysis showed that earthworms, estimated from both bristle and sand content, constituted a very large amount of the remains in the pellets, calculated as fresh weight on average approx . 77% of the biomass in the analyzed sample . Mammals and birds, especially mole (Talpa europaea), field vole and common vole (Microtus agrestis, M. arvalis), were few in numbers, but averaged approx . 16% of the calculated biomass, while a large number of insects (and a few mollusks), especially Carabidae, Dytiscidae, Silphidae, Geotrupidae, Aschnidae, Acrididae and Tipulidae, averaged only approx . 7% of the calculated biomass (fig . 12, p . 19) . Amphibians, often considered important food items of the White Stork, could hardly be traced, probably because their bones are dissolved by the stomach acid of the stork . However, the remains of very small insects, especially numerous in pellets from Vesløs, indicate that such storks have consumed amphibians, assuming that the small insects were primarily ingested by these amphibians . In case a stork predominantly feeds on amphibians fewer and smaller pellets will be produced, and urea and the microscopic bristles will to a higher extent be excreted by the vent (Cloaca) . Sand, primarily from digested earthworms, will still be disgorged and thus occur in a higher ratio compared to bristles than in other pellets . This was actually the case in Vesløs, but still it is difficult to estimate the amphibian biomass on this basis . Given the very irregular sampling practices it is difficult to draw definitive conclusions, but compared to previous Danish studies (Skovgaard, 1920) it seems evident that the White Storks used to consume more large insects (Carabus, Dytiscus, Geotrupes) than recently, when predominantly medium sized insects (Pterostichus, Silpha) were taken, presumably because several of the larger insect species have declined or become locally extinct . Also, amphibians and small mammals have become scarce in the cultivated Danish landscape and the large proportion of earthworms in the analyzed pellets indicate that earthworms gradually became the main food ressource of the Danish storks . Recent studies in Germany and Poland 5 (Dziewiaty & Schulz, 1998; Tryjanowski & al ., 2006) suggest that these populations to a much higher degree prey on mammals, amphibians or insects, as the habitats still provide these food items . Following several decades of decline the White Stork ceased breeding in Denmark around the turn of the millennium . One of the last nesting sites was Vesløs, still a good habitat, but now extremely isolated from the closest breeding population . The last breeding site was Ribe in SW-Jutland, where the habitat was gradually spoiled, but the storks survived from fishing in trout farms . However, since then a few breeding attempts have been made on Zealand by semi-domesticated storks originating from Sweden . Moreover, many White Storks still breed in NW-Germany, close to the Danish border, thus making it likely that the species could return as a breeding species if habitat conditions improve .
Page 1 and 2: En analyse af gylp fra hvid stork C
Page 3: Indhold Sammenfatning . . . . . . .
Page 7 and 8: Beskrivelse af storkegylpene De ana
Page 9 and 10: 4 . Den i sien tilbageværende, gro
Page 11 and 12: Serierne fra NV-Jylland (1: Vesløs
Page 13 and 14: på regnorme . Den blev fundet i p
Page 15 and 16: per, og begge indgår i storkens f
Page 17 and 18: driftsform end tidligere, og livsbe
Page 19 and 20: To metoder blev anvendt til estimer
Page 21 and 22: Tidligere undersøgelser Skovgaard
Page 23 and 24: Diskussion Det er velkendt, at stor
Page 25 and 26: BILAG 1 Beskrivelse af udvalgte lok
Page 27 and 28: Taxa ca . > Mg/eks . Behov/dag Sump
Page 29 and 30: Taxa (fortsat) Serie > VESL VANG VE
Page 31 and 32: UTM (fortsat) Lokalitet Anvendt g G

En analyse af gylp fra hvid stork Ciconia ciconia i Danmark

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