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Food Habits of the Grass Snake in Southeastern England: Is Natrix natrix a Generalist Predator?
Abstract
Generalist species are often both widely distributed and abundant. They also are often plastic in their ecology, both spatially and temporally, in response to variation in resources. Here, we study the food habits of the widespread European Grass Snake, Natrix natrix,in Kent in southeastern England. As elsewhere in their range, Grass Snakes at our study site mainly ate anurans (63%); however, small mammals also were fairly common in the diet (25%) and fish (10%) and birds (1%) were taken occasionally. About 65% of prey eaten by snakes were swallowed headfirst, but orientation of prey during ingestion varied among prey types. Although anurans are the major prey of Grass Snakes, the predominant species in their diet varies geographically, presumably in relation to availability; at our site, the most frequently eaten species (63%) was the introduced Marsh Frog, Rana ridibunda, which is very common and possibly influences abundance of snakes. We obtained few data on feeding habits of small snakes (< 400 mm SVL) but found anuran prey in the smallest snake in our sample; other prey types were eaten by larger snakes and therefore presumably are added to the diet as snakes grow. Maximum size of prey increased with snake size, but large snakes nonetheless continued to eat small prey as well. However, because Grass Snakes are sexually dimorphic (females larger), such size effects may be confounded with sex effects. Snakes had food in their stomachs less frequently in midsummer than they did in early and late summer. Nonetheless, even after adjusting for such seasonal variation, gravid females contained food less frequently than nongravid females. Thus, gravid females of this oviparous species apparently exhibit an anorexia similar to that seen in pregnant females of many viviparous species.
... T he Barred Grass Snake (Natrix helvetica) has been recorded as having a diet consisting mainly of amphibians and fish (Gregory and Isaac 2004). In Great Britain, European Common Frogs (Rana temporaria) undoubtedly are the principal prey, followed by newts, fish, and tadpoles (Gregory and Isaac 2004), but terrestrial vertebrates also are taken (Luiselli and Rugiero 1991). ...
... T he Barred Grass Snake (Natrix helvetica) has been recorded as having a diet consisting mainly of amphibians and fish (Gregory and Isaac 2004). In Great Britain, European Common Frogs (Rana temporaria) undoubtedly are the principal prey, followed by newts, fish, and tadpoles (Gregory and Isaac 2004), but terrestrial vertebrates also are taken (Luiselli and Rugiero 1991). However, different populations of Natrix helvetica are known to consume different prey. ...
... Regionally, the diets of Barred Grass Snake populations depend on factors that include prey availability and climatic conditions (Luiselli et al. 2005). One notable example of a regional diet was in Fordwich, where the main anuran prey was the alien Marsh Frog, Pelophylax ridibundus (Gregory and Isaac 2004). In southern England, Barred Grass Snakes feed almost exclusively on European Common Toads, with larger snakes taking larger toads (Reading and Davies 1996). ...
... The barred grass snake Natrix helvetica (Lacépède, 1789) is a recently recognised Colubridae Natricinae species (Kindler et al., 2017;Di Nicola, 2019;Uetz et al., 2020), previously considered as a subspecies of Natrix natrix (Linnaeus, 1758). It is a semi-aquatic snake and anuran amphibians represent the major prey items (Filippi et al., 1996;Reading and Davis, 1996;Gregory and Isaac, 2004;Luiselli et al., 2005). However, it cannot be considered a true specialist predator, since it is able to adapt its diet according to local preys' abundances and availabilities (Gregory and Isaac, 2004;Luiselli et al., 2005;Faraone et al., 2010). ...
... It is a semi-aquatic snake and anuran amphibians represent the major prey items (Filippi et al., 1996;Reading and Davis, 1996;Gregory and Isaac, 2004;Luiselli et al., 2005). However, it cannot be considered a true specialist predator, since it is able to adapt its diet according to local preys' abundances and availabilities (Gregory and Isaac, 2004;Luiselli et al., 2005;Faraone et al., 2010). For instance, different populations of N. helvetica are known to feed primarily on fish (e.g. ...
... For instance, different populations of N. helvetica are known to feed primarily on fish (e.g. Faraone et al., 2010) or small mammals (e. g. Gregory & Isaac, 2004), and occasionally birds (Luiselli and Rugiero, 1991;Gregory and Isaac, 2004) and even carrion (Luiselli et al., 2005;Faraone et al., 2010). Since previous diet data were obtained through stomach contents and scat analysis, it is unknown if birds are actively predated or if they are consumed as carrion. ...
... A kockás sikló és a vízisikló prédáinak prezencia-abszencia (jelenlét-hiány) adataival asszociáltság elemzést végeztem nem metrikus-klaszterelemzéssel (non-metric cluster analysis) (Goodall 1953, Podani 1997, Williams & Lambert 1960 Mennyiségi adatokat is tartalmazó tudományos közleményből a kockás sikló esetén kilenc (Acipinar et al. 2006, Bakiev et al. 2011, Filippi et al. 1996, Göçmen et al. 2011, Hutinec & Mebert 2011, Luiselli et al. 2007Sloboda et al. 2010;Zimmerman & Fachbach 1996), a vízisiklónál pedig tizenegy (Capual et al. 1994, Filippi et al. 1996, Filippi & Luiselli 2002, Gregory & Isaac 2004, Hutinec & Mebert 2011, Luiselli et al. 1997, 2005, Luiselli & Rugiero 1991, Reading & Davies 1996, Braňa 1998 A kockás siklóval kapcsolatos nyolc közleményből hétben legnagyobb mennyiségben halfogyasztást regisztrálták (Acipinar et al. 2006, Bakiev et al. 2011, Filippi et al. 1996, Göçmen et al. 2011, Hutinec & Mebert 2011, Luiselli et al. 2007, Sloboda et al. 2010, Zimmerman & Fachbach 1996, a száraz közép-törökországi vizsgálatban szerepelnek csak nagyobb mennyiségben más állatcsoportok. Négy vizsgálatban (Ausztria, Horvátország, Észak-Törökország, Románia) csak halfogyasztást, míg a Olaszország északi és középső területein gyűjtött mintákban a kétéltűek, az oroszországi vizsgálatokban pedig hüllőfajok jelenlétét is kimutatták a táplálékban. ...
... A három faj közül kiemelkedik a Savi-földipocok (Microtus savii), mely a mezőgazdasági terület jellegű élőhelyen az összes préda 38%-át adta (Luiselli et al. 2005). A részletesebb vizsgálatok a vízisiklónál nem igazolták a gerinctelen fajok fogyasztását, de a kockás siklóval ellentétben minden vizsgálatban, legalább két (Capual et al. 1994, Filippi et al. 1996, Filippi & Luiselli 2002, Hutinec & Mebert 2011, Luiselli et al. 1997, 2005, Luiselli & Rugiero 1991, Reading & Davies 1996, Braňa 1998, egy angliai vizsgálatban négy rendszertani csoport előfordulását igazolták a faj táplálékban (Gregory & Isaac 2004). Mivel kiválóan úszik és nagyobb mélységekbe is képes táplálékszerzés céljából lemerülni, továbbá rejtő színezete folytán a növényzet, valamint a part menti élőhelyeken könnyen el tud rejtőzni, így a vizes élőhelyeken a kockás sikló kiváló képességgel rendelkezik, hogy az elsődlegesen halakból álló táplálékát megfogja (Gasc et al. 1997, Kreiner 2007. ...
... halak, kétéltűek lárvái képezik (Hutinec & Mebert 2011 (Ahmadzadeh et al. 2011, Bakiev 2004, Capula et al. 1994, Drobenkov 1995, Filippi et al. 1996, Luiselli & Capula 1997, Luiselli et al. 2005, de saját gyűjtéseim során Magyarország esetében is lét gyíkfaj (Lacerta agilis, L. viridis) fogyasztását igazoltam. Az adatok alapján a kisemlősök jelentenek még fontos táplálékot a vízsikló számára, főleg az elterjedési területének déli és nyugati térségeiben, valamint azon élőhelyeken, ahol bizonyos rágcsáló fajok nagy tömegben találhatóak (Filippi et al. 1996, Gregory & Isaac 2004, Luiselli & Capula 1997, Luiselli et al. 2005. A madarak közül egy faj (Turdus merula) és egy genus (Passer sp.) fiatal egyedei igazolják, hogy a vízisikló fákra és bokrokra is felhatol táplálékszerzés céljából (Luiselli et al. 2005). ...
Doktori munkám két fő célkitűzése (i) a kockás sikló, a vízisikló és potenciális táplálékszervezeteik tér- és időbeli dinamikájának megismerése a Duna három mellékvízfolyáson, az Ipolyon, a Sződrákos-patakon és az Ilka-patakon, azok torkolati és a torkolatok körüli dunai szakaszokon, (ii) valamint hazánk öt régiójában, a Balaton, a Dráva, a Duna, a Koppány és a Tisza-tó térségében gyűjtött egyedek táplálék vizsgálatának összehasonlítása a szakirodalmi adatokkal. A kutatásaim során a következő kérdésekre kívántam válaszokat adni.
1. Hogyan alkalmazkodik a kockás sikló és a vízisikló az eltérő vízjárások hatására megváltozó táplálék készlethez és ezzel párhuzamosan hogyan változik az élőhely preferenciájuk a három folyó-mellékfolyó rendszerben.
2. Milyen fajokat fogyaszt a kockás sikló és a vízisikló hazánk öt különböző területén és az itt gyűjtött adatok milyen összefüggéseket mutatnak a két Natrix-faj teljes elterjedési területéről származó adatokkal. /
The two aims of my doctoral thesis are (i) to understand the temporal and the spatial dynamics of the dice snake, the grass snake and their potential prey items in three tributaries of River Danube, in River Ipoly, in Sződrákos and Ilka stream and the estuaries section in River Danube and (ii) to compare the prey composition of sampled individuals at five areas of Hungary to the data of specialist literature. My study is aimed to give answers to the following questions:
1. How the dice snake and the grass snake adapt to the different prey composition parallel with the habitat preferences in different water level fluctuation in the three river-tributary systems.
2. Which species the dice snake and the grass snake eat in the five different areas of Hungary, and what relationships are shown between the sampled data and the data from the whole distribution area of both Natrix species.
... Meanwhile, common toad populations achieved good breeding populations (100+ toads, Nature Conservancy Council 1989), peaking in 2004 and 234 respectively), but thereafter declined. Grass snakes vary the anuran species that they prey on, depending on what is available, so it is likely that marsh frogs have become part of the grass snake diet in lieu of common frogs or common toads (Gregory and Isaac 2004). Marsh frogs have not been surveyed at LWC since the mid-2000s but appear to have declined in at least the past five years (pers. ...
... Both of these species are present at LWC. Luiselli et al. (2005) suggest that declines in amphibian prey may not be a serious problem, as grass snakes could shift their preference to different prey such as fish. However, this theory is based on comparisons made between several populations which have different diets (see also Gregory and Isaac 2004), rather than observing one population altering their diet, and it cannot necessarily be assumed that this would happen at LWC. ...
Translocation of species is a controversial conservation technique which is widely used but often has unknown outcomes. In the mid-2000s, populations of slow worm Anguis fragilis and grass snake Natrix natrix were translocated to a nature reserve in southwest London. A refugia-based survey of these reptiles has been running since their introduction, and this paper evaluates the success or otherwise of the releases. A total of 72 refugia were distributed across the reserve and the reptiles found under these were counted. The highest count for each year was used as a metric for comparison. Additionally, half of these refugia were made of felt and the other half made of tin, allowing a comparison of refugia material preference, by species and by age group. Analysis of refugia material preferences showed slow worms had a significant preference for felt refugia, while grass snakes showed a significant preference for tin refugia. These findings allow a future survey to target individual species more effectively. Good quality habitat has benefitted the slow worm population. They appear to be breeding in increasing numbers, and are spreading across the reserve. The grass snake population appeared to start well and began breeding rapidly, but after an initial peak, numbers of juveniles dropped substantially; adult numbers remain low. There are two likely causes of the grass snake decline: poor quality compost heaps, a vital breeding location for the species; and declining populations of breeding amphibians, their primary food source. This informs future translocation plans of the importance of these factors in grass snake translocation success. The long-term monitoring of these species has revealed the plight of the grass snake at the study site, allowing action to be taken before it is too late. This demonstrates the importance of long-term monitoring for the survival of translocated species.
... There are various methods to study wild snake diets, including direct behavioral observations (Novak and Wootton 2008;Grundler and Rabosky 2021;Durso et al. 2022), the collection of stomach contents through either regurgitation or dissection (Sunderland et al. 1987;Gregory and Isaac 2004), and morphological or molecular fecal analysis (Ford et al. 2016). Molecular fecal analysis has a high prey detection probability and is relatively noninvasive (Taberlet et al. 1999;Sheppard and Harwood 2005). ...
... The number of fecal analysisebased diet studies has recently increased (Symondson 2002;Carreon-Martinez and Heath 2010). Nevertheless, induced regurgitation collection methods are preferred when snakes have relatively undigested prey items within their digestive tract (Gregory and Isaac 2004). Studies often combine both molecular and morphological analysis to determine the breadth of wild snake diets (Tesler et al. 2019;Park et al. 2021). ...
Understanding snake prey breadth, within forest ecosystems, may elucidate their ecological role. We determined the prey items of 35 individuals of 4 snake species (11 through induced regurgitation analysis and 24 through molecular fecal analysis) collected from 5 mountain forests between May 2016 and October 2018, located within South Korea. Snake prey breadth spanned across six small mammal (four rodents and two shrews) and five amphibian (two urodeles and three anurans) species. Small mammals were more frequently detected as prey items than amphibians but the proportion between small mammal and amphibian prey varied by different snake species. Two rodent prey species, Mus musculus and Craseomys regulus, made up 68.6% of the total amount of prey consumed (24 out of 35 prey items). Elaphe dione and Gloydius intermedius samples contained only small mammal prey remains, while Rhabdophis lateralis and G. ussuriensis appeared to predate both small mammals and amphibians. These findings show snakes’ role in controlling small mammal population sizes in mountain forests and highlight the importance of conserving snake biodiversity native to South Korean mountain forests.
... B arred grass snakes (Natrix helvetica) are found throughout north-west Europe (Kindler & Fritz, 2017) and potentially grow to 1.5 m but rarely attain this size (Speybroeck et al., 2016). They are thought to feed primarily on amphibians and are adept swimmers although rarely seen hunting in open water (Gregory & Isaac, 2004). ...
... It is also likely that the snake was swallowed whole whilst it was traversing the small river. The occurrence of fish within a grass snake diet is well documented (Gregory & Isaac, 2004); however, there are no scientific reports of fish predating N. helvetica or other Natrix spp. There are, however, online references to grass snakes forming part of the diet of Pike (Esox lucius). ...
Natural history record of trout predation on Natrix helvetica
... The grass snake is considered a generalist species. It feeds on amphibians, mostly anurans [61][62][63], but its diet varies with geographical location, habitat or competitor's presence and may include also small mammals, other reptiles and fish [62,64]. Among its most common prey species are Bufo bufo, Rana temporaria and Lissotriton vulgaris [61][62][63]. ...
... It feeds on amphibians, mostly anurans [61][62][63], but its diet varies with geographical location, habitat or competitor's presence and may include also small mammals, other reptiles and fish [62,64]. Among its most common prey species are Bufo bufo, Rana temporaria and Lissotriton vulgaris [61][62][63]. Based on this literature, we compiled occurrence data from GBIF [56] for these three species and six more species that were referenced in at least one study and represent various classes (amphibians, other reptiles, small mammals) in Europe. ...
The ongoing climate change and the unprecedented rate of biodiversity loss render the need to accurately project future species distributional patterns more critical than ever. Mounting evidence suggests that not only abiotic factors, but also biotic interactions drive broad-scale distributional patterns. Here, we explored the effect of predator-prey interaction on the predator distribution, using as target species the widespread and generalist grass snake (Natrix natrix). We used ensemble Species Distribution Modeling (SDM) to build a model only with abiotic variables (abiotic model) and a biotic one including prey species richness. Then we projected the future grass snake distribution using a modest emission scenario assuming an unhindered and no dispersal scenario. The two models performed equally well, with temperature and prey species richness emerging as the top drivers of species distribution in the abiotic and biotic models, respectively. In the future, a severe range contraction is anticipated in the case of no dispersal, a likely possibility as reptiles are poor dispersers. If the species can disperse freely, an improbable scenario due to habitat loss and fragmentation, it will lose part of its contemporary distribution, but it will expand northwards.
... Les récents travaux génétiques effectués sur le genre Natrix (Kindler et al., 2013 ;Pokrant et al., 2016 ;Kindler et al., 2017Kindler et al., , 2018 (Arnold and Ovenden, 2010). Cette couleuvre affectionne les milieux humides où elle trouve sa principale source de nourriture, à savoir tous types d'amphibiens (Gregory and Isaac, 2004). Elle évolue donc à proximité des milieux aquatiques où elle thermorégule et attrape ses proies principalement dans l'eau (Arnold and Ovenden, 2010). ...
... Grass snakes are non-venomous and are the most common snake species in Europe with a wide geographical range. Their typical habitats are wetlands and their diet mainly consists in amphibians (Gregory and Isaac, 2004). ...
La mise en place des réseaux de continuités écologiques dans les paysages nécessite l'estimation de la connectivité fonctionnelle, particulièrement lorsque ces paysages sont fragmentés par les Infrastructures Linéaires de Transport (ILT). Dans ce contexte, des suivis génétiques et démographiques ont été réalisé sur quatre espèces terrestres dans un paysage fragmenté par six types d'infrastructures en Dordogne, France. Les résultats ont montré qu'une part importante de la variabilité génétique (38 %) est expliquée par les ILT, qui agissent majoritairement comme des barrières à la dispersion. Cependant, les effets des ILT varient fortement d'une espèce à l'autre et peuvent, dans certains cas, agirent comme des éléments favorisant la dispersion. Par ailleurs, l'utilisation conjointe des outils de génétique du paysage et des suivis démographiques montre que selon l'approche utilisée, les résultats peuvent diverger. Ces deux approches devraient donc être davantage utilisées simultanément dans les études paysagères.
... Les récents travaux génétiques effectués sur le genre Natrix (Kindler et al., 2013 ;Pokrant et al., 2016 ;Kindler et al., 2017Kindler et al., , 2018 (Arnold and Ovenden, 2010). Cette couleuvre affectionne les milieux humides où elle trouve sa principale source de nourriture, à savoir tous types d'amphibiens (Gregory and Isaac, 2004). Elle évolue donc à proximité des milieux aquatiques où elle thermorégule et attrape ses proies principalement dans l'eau (Arnold and Ovenden, 2010). ...
... Grass snakes are non-venomous and are the most common snake species in Europe with a wide geographical range. Their typical habitats are wetlands and their diet mainly consists in amphibians (Gregory and Isaac, 2004). ...
... Scali (2011) does note that in Sardinia there's a strong competition between viperine snakes and grass Niet alleen dobbelsteenslangen en adderringslangen kunnen hun dieet verschuiven, ook ringslangen blijken exibel. Het opportunistische karakter van deze slangen blijkt uit een onderzoek, uitgevoerd in Zuidoost-Engeland; ringslangen eten naast am bieën (63%), ook zoogdieren (25%), vis (10%) en vogels (1%) (Gregory & Isaac, 2004). Bij een schaarste van am bieën kan het aandeel andere prooien hoger liggen (Creemers & Van Delft, 2009). ...
... Not only dice snakes and viperine snakes can change their diet, grass snakes also seem exible. The opportunistic character of these snakes shows through in a research, done in southeast England; grass snakes also eat mammals (25%), sh (10%) and birds (1%) besides amphibians (63%) (Gregory & Isaac, 2004). With a shortage of amphibians, the relative proportion of other prey can be higher (Creemers & Van Delft, 2009). ...
www.waterslangen.nl Inleiding Jaren geleden, toen ik als gastmedewerker bij Naturalis werkte, stelde een Italiaanse weten-schapper mij een mooi vooruitzicht. Noord-west-Italië, dat was het gebied waar ik heen moest, daar kwamen alle waterslangen van Europa voor (Fig. 1, 2 en 3). Dat klonk als het beloofde land: een gebied waar adderring-slangen (Natrix maura) en dobbelsteenslangen (Natrix tessellata) samen voorkomen met ring-slangen (toentertijd nog één soort Natrix natrix). Samen voorkomen is in dit geval eerlijk gezegd een misleidende uitspraak. Het is waar dat ad-derringslangen en dobbelsteenslangen samen worden aangetroffen in hetzelfde gebied, nota-bene in dezelfde rivier, de Trebbia (Scali, 2011), maar de overlap is werkelijk maar een fractie van de immens grote verspreidingsgebieden van beide soorten. Een stukje naar het westen en je komt alleen nog maar adderringslangen tegen (Fig. 2), een stukje naar het oosten en je vindt alleen nog maar dobbelsteenslangen (Fig. 3). Dat maakt het beloofde land wel erg klein. De term 'uitsluiten' is toepasselijker wat betreft het voorkomen van deze twee slangen-soorten. De verspreiding van beide soorten in ogenschouw nemend, drong bij mij het princi-pe van competitieve exclusie, zich vanzelf op. Grofweg komt dit principe (Hardin, 1960) erop neer dat binnen een geograsch gebied twee soorten, die precies dezelfde ecologi-sche niche bezetten, niet naast elkaar kunnen Paul Storm Biology lecturer, University Rotterdam www.waterslangen.nl
... Przykładowo zaskroniec zwyczajny (Natrix natrix) gryzie nadętą ropuchę od tyłu, zmuszając ją do wypuszczenia powietrza z płuc. Dzięki zastosowaniu tej taktyki może bez problemu połknąć ofiarę [2,4]. Natomiast badania własne wykazały, że nadymanie ciała jest nieskuteczną strategią w przypadku ataku jeża. ...
... Co ciekawe, pewne drapieżniki wydają się być odporne na działanie niektórych toksyn. Przykładowo zaskrońce odporne są na truciznę ropuchy szarej [1,2,4]. Badania własne sugerują, że również jeże: wschodni i zachodni odporne są na toksyny Bufo bufo. ...
European anurans are prey for a variety of predators, against which they have evolved a range of defense behaviors. We investigated defensive behaviors of three European anurans: the Common Toad (Bufo bufo), the Common Frog (Rana temporaria), and the Edible Frog (Pelophylax esculentus) during interactions with a predator (hedgehog) and a control stimulus (rabbit).We hypothesized that (H1) due to small capacity to flee quickly from a predator, B. bufo has evolved a more diverse repertoire of behavioral defenses than the ranids, R. temporaria and P. esculentus. We also hypothesized that (H2) B. bufo can minimize the secretion of metabolically costly poison through behavioral control. According to our predictions, the repertoire of defensive behaviors was more complex in B. bufo than in the ranids. Also, the number of threatening behaviors was higher in toads than in both frog species. Fleeing was the most common response employed by all tested anurans. We report a new anti-predator behavior in the Common Toad: head hitting. As B. bufo released the poison only after squeezing of parotoid macroglands by the predator, we conclude that the Common Toad can minimize poison release through behavioral control. Our data suggest that length of hind-legs and, related to this, mode of locomotion (jumping vs. hopping) can affect anti-predator behavior in anurans.
... We predicted that if foraging copperheads were exhibiting some form of acclimatization to capture and increase in tolerance to human presence at a foraging site, it would occur in the Fig. 5 Predicted count of nights an individual copperhead forages per sampling season as a function of the number of years the individual has been captured at the site. Model prediction with 95% CI is overlaid with collected data used to generate the model are no doubt present on the landscape (Gregory and Isaac 2004), grass snakes do not have a single focal point of prey aggregation. Comparatively, copperheads in our study system are almost certainly selecting our site to actively forage. ...
To maximize energy available for foraging or reproduction, optimality theory suggests individuals allocate energy toward defensive behaviors equivalent to risk of predation. In this framework, repeat encounters with humans by wildlife that do not reduce individual fitness could result in a decreased defensive response toward humans in subsequent encounters. We investigated whether individual experience influenced the defensive behaviors and frequency of site use of foraging eastern copperheads (Agkistrodon contortrix) at Koomer Ridge Campground in the Daniel Boone National Forest, Kentucky. Beginning in 2015, this site has been used for annual mark-recapture studies of copperhead foraging ecology as they predate emerging annual cicadas (Neotibicen tibicen). Using a standardized behavioral trial, we tested how copperhead defensive behavior toward humans was influenced by capture history, body size, and soil temperature. Model averaging results indicated that the overall intensity of copperhead defensive response to humans increased with capture history length, and soil temperature was positively associated with likelihood to respond when touched. Number of years recaptured was a significant, positive predictor of foraging frequency in 2022. Therefore, copperheads with longer capture histories visit the site to forage more frequently and are more willing to defend their opportunity to forage, suggesting a degree of acquired tolerance absent from naïve snakes that fled readily. Collectively, these results provide evidence that eastern copperheads at our site modulate their foraging and defensive behavior based on previous capture experience to more efficiently predate a seasonally abundant prey item.
... Snakes are gape-limited predators and need to minimize the resistance caused by the prey's appendages or body scales to swallow the prey efficiently (Greene 1976;Cundall and Greene 2000). Thus, except for a few cases (e.g., Krause and Burghardt 2001;Gregory and Isaac 2004;Mori 2006), headfirst ingestion is a general rule in snakes when they swallow relatively large prey because it should make swallowing easier and consequently reduce total prey-handling time and energy expenditure (e.g., Diefenbach and Emslie 1971;Greene 1976Greene , 1989Cundall and Greene 2000;Rodríguez-Robles 2002;Mori 2006). Our results did not show this tendency: snakes swallowed earthworms and firefly larvae from inconsistent directions, including anterior-first, posterior-first, and folded ingestion. ...
Dietary specialists consume specific prey items, and they are often morphologically and behaviorally specialized to feed efficiently on those prey animals. Among specialist snakes, consumption of terrestrial arthropods is relatively rare. Because most terrestrial arthropods possess hardened sclerites and appendages, it is possible that snakes that feed on arthropods would show specialized prey-handling behavior. In this study, we describe prey-handling behavior of a snake feeding on terrestrial arthropods, which hitherto has not been well documented. We focused on Rhabdophis chiwen, which mainly feeds on earthworms, but also consumes lampyrine firefly larvae, sequestering cardiotonic steroids from them in its defensive organs, called nucho-dorsal glands. When feeding on earthworms, snakes showed size-dependent selection of swallowing direction, but this tendency was not observed when feeding on firefly larvae. Manipulation of firefly larvae did not seem to be efficient, probably because they possess sclerites and appendages such as legs that impede smooth handling. Although fireflies are an essential food for R. chiwen as a toxin source, our results showed that the snake is not adept at handling firefly larvae compared to earthworms, implying that dietary specialization does not necessarily accompany behavioral specialization. We discuss possible reasons for this inconsistency.
... Concerning MIHB, it is likely that the higher abundance of N. natrix in sites with high stem density of reeds can be explained by trophic reasons, as this species is essentially batracophagous (Gregory and Isaac 2004;Luiselli et al. 2005), and the density of frogs (Pelophylax ridibundus) at the study area was much higher in spots with high reed stem density than in more open spots (Luiselli et al., unpublished observations). It is also noteworthy that four N. natrix captured during this study regurgitated four adult P. ridibundus, indicating perhaps that this frog represents the bulk of the diet of this snake in the study area. ...
Reed bed ecosystems are crucial for the survival of complex animal communities in Europe and Western Asia, but have been subjected to considerable decline, especially in beds in eutrophic shallow lakes, throughout Europe during
the last decades. In Western Asia, however, these ecosystems are still wide and ecologically intact, and support highly biodiverse communities of species, including some highly threatened taxa. Here, we studied the spatiotemporal
community dynamics of semi-aquatic reptiles in a wide reed bed biotope in Azerbaijan, and present conservation considerations for its optimal management for the survival of the authochtonous reptile species. Three reptile species (two snakes, Natrix natrix and Natrix tessellata, and one turtle Emys orbicularis persica) were
found in the study area. Activity intensity was not even throughout the years, and was significantly more related to ambient temperatures in 2016 than in 2017. Interestingly, amphipod abundance was also significantly different
between years, and correlated well with the differences in activity patterns observed in a turtle species. There were complex spatio-temporal patterns exhibited by the reptile species at the study area, with an excess of reptile
individuals in the high density reed bed habitat during summertime whereas there was an excess of individuals in the open reed bed habitat in spring and autumn. This evidence suggests that there should be seasonal interhabitat
movements of reptiles at the study area, and that the reed beds are not perceived as a homogeneous habitat by reptiles. Several hypotheses are presented to explain these unexpected spatio-temporal patterns by reptiles in reed beds. Our study clearly shows that, in order to enhance the conservation of reptiles, it is important to keep a mosaic of areas with dense reed stands (high density of young stems) and of open reed stands (lower density of older stems), thus increasing habitat heterogeneity and favouring small-scale ecological key-structures.
... Barred grass snakes were commonly seen in the nearby area prior to habitat modification (5%-17% of their reserve sightings) but were only observed in the bank area after basking bank creation; sightings were low across the reserve in 2022 with 60% in the bank area. Barred grass snakes commonly hunt fish and amphibians (>70% of their diet; Gregory & Isaac, 2004) and the reserve has many ponds; hence, the banks may be attractive places to warm up after hunting in water. While refuge sharing was not observed, some evidence suggests that barred grass snakes may prefer areas used by European adders (Brown, 1991). ...
Reptiles are often overlooked in conservation efforts. Hence, long‐term population data is often unavailable, and evidence for effective conservation actions that improve reptile habitat remains scarce for most species. Here we used a before–after control–intervention (BACI) experiment to investigate the impact of basking bank creation on four co‐occurring reptile species: European adder, barred grass snake, slow worm, and viviparous lizard. Long‐term refuge monitoring at a UK wildlife reserve allowed population assessment before and after habitat modification. Only viviparous lizards were observed at basking banks within 12 months of construction. In subsequent years, barred grass snake observations increased near basking banks and slow worms were observed for the first time, while European adder observations increased away from banks and barred grass snake observations decreased away from banks. Our small‐scale BACI study suggests basking banks attracted barred grass snakes from the surrounding area, which saw a corresponding increase in European adder sightings.
... Another aquatic snake species, the grass snake (Natrix natrix), also occupies certain sites included in our study. However, unlike dice snakes, which primarily prey on fish, grass snakes predominantly consume amphibians (Gregory and Isaac 2004) which are predominantly found in dense reed beds and wetlands and not around the rocky shoreline. We believe that this dietary contrast and preferred habitat differences likely mitigates competition between the two species. ...
Context
Human-induced landscape modification, such as urbanization, creates new environments that can have adverse effects on flora and fauna, posing threats to biodiversity. Understanding how reptiles respond to urbanization is crucial, especially in light of their ongoing population declines.
Objectives
We examined the influence of landscape-scale and local-scale urbanization features on the abundance of an aquatic snake species. Our investigation focused on dice snakes (Natrix tessellata) inhabiting a lake with a heavily urbanized shoreline.
Methods
We conducted visual encounter surveys at 25 study sites during the activity period of dice snakes around Lake Balaton in Hungary. We measured both landscape-scale and local-scale variables, including urban land use cover, vegetation cover, road cover, distance of main roads and city size, emergent vegetation cover and the area of artificial rock and concrete shoreline protection structures. We analysed snake survey data using N-mixture models to estimate abundance and examine relationships with landscape-scale and local-scale variables.
Results
Urban land use cover, road cover, the proximity of main roads and the extent of artificial rock and concrete shoreline protection structures positively affected the abundance of snakes. These findings imply that urban habitats may offer new ecological opportunities for dice snakes.
Conclusions
The findings of this study indicate that both landscape-scale and local-scale human-induced landscape modifications may have a positive impact on the abundance of urban snakes. Taken together, our findings suggest that urbanization is a complex phenomenon, affecting species at different levels and with subtle effects.
... As such, the highly aquatic N. maura and N. tesellata feed almost exclusively on anurans (frogs and toads) and fish, with some seasonal variation due to availability and juvenile snakes capturing amphibian larvae (Filippi et al., 1996;Santos & Llorente, 1998;Santos et al., 2000). The less aquatic grass snakes, Natrix natrix complex, are less specialized eating also anurans and fish but also small mammals and even birds (Filippi et al., 1996;Gregory & Isaac, 2004). ...
This report is a product of the COST Action CA18221 PERIAMAR, PEsticide RIsk AssessMent for Amphibians and Reptiles
As part of the pesticide risk assessment, a characterization of the exposure of amphibians and reptiles to pesticides is necessary. In the first-tier assessment, it is common practice to estimate pesticide exposure using worst-case scenarios and simplified models, while in higher tiers the exposure assessment is refined based on a wider range of environmental parameters that affect pesticide fate and degradation and more sophisticated modelling approaches. Despite the use of pesticide models, refined exposure assessments require a good understanding of the ecological scenario in which the species inhabits, including potential exposure pathways, life cycle characteristics and biological traits that make each species vulnerable to pesticide pollution (Rico et al. 2016). Therefore, the aim of this paper is to review those aspects of amphibian and reptilian biology, ecology and ecophysiology that should be taken into account for the high-tier exposure assessment of pesticides. By reviewing aspects of the ecology and physiology of amphibians and reptiles, we aim to improve our understanding of the presence and activities of animals in the areas that may be exposed to pesticides and, consequently, contribute to identify key exposure routes and scenarios. This review also provides recommendations for further research to complete a useful scheme for the pesticide exposure assessment of herpetofauna.
The full report is available at: https://periamar.com/assets/Uploads/482e81020a/Deliverable_04+06.pdf
... Recent analysis of museum specimens found evidence of Oo in N. helvetica since at least 1959 in Italy, and 1961 in N. tessellata in Switzerland 19 . All three of these Natrix species are semi-aquatic predators, primarily of amphibians and fish 20,21 . ...
Ophidiomycosis is an emerging infectious disease affecting wild snakes in the Northern Hemisphere. Recently confirmed in Great Britain, the prevalence, severity and significance of ophidiomycosis has yet to be characterised in free-living snakes at a population level in Europe. Therefore, a population of barred grass snakes (Natrix helvetica) in eastern England was monitored for three seasons (May 2019 to October 2021), to investigate the prevalence (25.5%; 191/750 snakes) and severity of skin lesions and their aetiology. The most frequently observed skin lesion characteristics were changes in scale colour, crusting, and scale margin erosion. The majority of such lesions (96.9%; 185/191 snakes) was observed on the ventral surface along the length of the body. The severity of skin lesions was considered mild in more than half of the cases (53.1%; 98/191 snakes). Predominantly, skin lesions were observed in adult snakes (72.8%; 139/191 snakes). Combined histological examinations and qPCR tests of skin lesions from N. helvetica sloughs and/or carcasses confirmed a diagnosis of ophidiomycosis. Further targeted surveillance, supported by molecular and histological examinations to confirm skin lesion aetiology, is required to determine the extent to which our findings reflect the occurrence of ophidiomycosis in populations within wider landscapes.
... I n Great Britain, the barred grass snake Natrix helvetica is widespread throughout most of England and Wales, with a limited distribution in Scotland (Cathrine, 2014). It is a semi-aquatic predator living in close proximity to water and in a site in southern England was found to feed mostly on amphibians and fish (73%), small mammals (25%) and just rarely on birds (1%) (Gregory & Isaac, 2004). A listing of ten bird species that have been observed as prey of Natrix spp in Britain and mainland Europe is given by Di Nicola & Zabbia (2021). ...
... Species with wide ranges are often generalist consumers suited for a large breadth of environmental conditions, but populations can be specialized to the local conditions of their habitat, such as prey availability, creating significant population-level differences (Brown 1995;Gregory & Isaac 2004;Obrist et al. 2022). In addition, individuals within a population can show unique resource partitioning and prey selection (Bolnick et al. 2003;Roughgarden 1972). ...
Marine resource subsidies alter consumer dynamics of recipient populations in coastal systems. The response to these subsidies by generalist consumers is often not uniform, creating inter- and intrapopulation diet variation and niche diversification that may be intensified across heterogeneous landscapes. We sampled western fence lizards, Sceloporus occidentalis , from Puget Sound beaches and coastal and inland forest habitats, in addition to the lizards’ marine and terrestrial prey items to quantify marine and terrestrial resource use with stable isotope analysis and mixing models. Beach lizards had higher average δ ¹³ C and δ ¹⁵ N values compared to coastal and inland forest lizards, exhibiting a strong mixing line between marine and terrestrial prey items. Across five beach sites, lizard populations received 20–51% of their diet from marine resources, on average, with individual lizards ranging between 7 and 86% marine diet. The hillslope of the transition zone between marine and terrestrial environments at beach sites was positively associated with marine-based diets, as the steepest sloped beach sites had the highest percent marine diets. Within-beach variation in transition zone slope was positively correlated with the isotopic niche space of beach lizard populations. These results demonstrate that physiography of transitional landscapes can mediate resource flow between environments, and variable habitat topography promotes niche diversification within lizard populations. Marine resource subsidization of Puget Sound beach S. occidentalis populations may facilitate occupation of the northwesternmost edge of the species range. Shoreline restoration and driftwood beach habitat conservation are important to support the unique ecology of Puget Sound S. occidentalis.
... Their base colour can be quite variable, mostly a shade of grey, and they usually have a yellow-black bordered collar, which also might be an aposematic feature in juvenile individuals (Madsen, 1987). They prefer mostly wetland habitats, however, they occur in many different types as well, even in sandy grasslands where they mostly prey on small rodents (Gregory and Isaac, 2004;Hojati et al., 2012). ...
The Hungarian meadow viper (Vipera ursinii rakosiensis) is an endangered subspecies of Vipera ursinii, which faces
high predation pressure, partially due to avian species. To create a systematic method for estimating the measure
of predation pressure, we developed a geometric morphometric approach to identify both undamaged and
damaged vertebrae of snake species found in Hungarian meadow viper habitats from raptor feeding remains. We
used linear discriminant analysis with a reference material of vertebrae from identified snake species as training
data. We also tested its efficiency by predicting the identification results of different simulation levels based on
vertebra completeness. We practiced this method on vertebrae of unknown species of snakes obtained from nests
and pellets of short-toed snake eagles (Circaetus gallicus, n = 9), common buzzards (Buteo buteo, n = 14) and
Montagu's harriers (Circus pygargus, n = 3). The identification approach showed high accuracy, even in the case
of missing landmarks to some extent. We identified vertebrae remnants of Natrix natrix (n = 172, 83.9%),
Coronella austriaca (n = 10, 4.9%) and V. u. rakosiensis (n = 23, 11.2%). Both, the reptile specialist C. gallicus and
the generalist B. buteo proved to be preying on V. u. rakosiensis, while samples of C. pygargus did not contain any
snake remains despite of previous observations of V. ursinii predations. Our approach is applicable for other
studies and taxa as well, therefore can be a practical tool for classification of incomplete vertebrae, which is
otherwise hardly identifiable. Furthermore, it could be applied to help estimate predation pressure on endangered snake species.
... Based on the limited data available, the dietary habits of N. h. cetti seem to differ from the habits of mainland grass snakes [89], where the diet of the latter includes a broader variety of prey items, such as fish and other terrestrial vertebrates (e.g., [89][90][91][92][93][94][95][96][97]). In fact, among 12 food items collected from specimens of N. h. ...
The Sardinian grass snake, Natrix helvetica cetti, is an endangered endemic snake subspecies with a restricted and highly fragmented geographic distribution. Information on its ecology and detailed geographic distribution are scarce and may negatively impact on its conservation status. Therefore, a literature review on its taxonomy, morphology, ecology, and conservation is presented here. Moreover, field records from the authors, citizen science and the existing literature provide an updated geographic distribution highlighting its presence within 13 new and 7 historic 10 × 10 km cells. Bioclimatic niche modelling was then applied to explore patterns of habitat suitability and phenotypic variation within N. h. cetti. The geographic distribution of the species was found to be positively correlated with altitude and precipitation values, whereas temperature showed a negative correlation. Taken together, these outcomes may explain the snake’s presence, particularly in eastern Sardinia. In addition, analysis of distribution overlap with the competing viperine snake (N. maura) and the urodeles as possible overlooked trophic resources (Speleomantes spp. and Euproctus platycephalus) showed overlaps of 66% and 79%, respectively. Finally, geographical or bioclimatic correlations did not explain phenotypic variation patterns observed in this highly polymorphic taxon. Perspectives on future research to investigate N. h. cetti’s decline and support effective conservation measures are discussed.
... In the USA, red clover crops are associated with much increased vole populations, where Microtus pennsylvanicus commonly prefers red clover to other crops (Thompson, 1965;Prieur & Swihart, 2020) and the European common vole Microtus arvalis prefers red clover to cereals (Lantová & Lanta, 2009); it is assumed that in Britain the field vole Microtus agrestis would have a similar dietary preference. Voles are an important food source for vipers (Smith, 1951) and in the case of grass snakes it has been suggested that in southeastern England that 25 % or more of their diet may consist of small mammals (Gregory & Issac, 2004). An increase in vole numbers could both attract more snakes to the field margin and provide a more abundant food supply. ...
In Britain, some reptiles species have been formally recorded inhabiting arable field margins but previous reports on the incidence of northern vipers or adders Vipera berus in this situation have been anecdotal. In 2017, reptile monitoring was initiated in a field margin that had been created ten years earlier and was located near two chalk grassland nature reserves with established viper populations. In the first three years of recording, numbers of vipers in the field margin were low and
limited to a few juveniles and adults. In the fourth year, there was a noticeable increase in number, which were now represented by all life stages. In the fifth year the population doubled again and then remained stable in the sixth year. A similar encounter trajectory was observed for grass snakes, while slow worms and common lizard encounters had different trajectories. There was some evidence of vipers moving between the nature reserves and field margin, even crossing a road to do so, but at least 75 % of vipers in the field margin were only ever detected there. The arable field was mostly used for cropping cereals and oilseeds but, exceptionally, in the three years from 2016 to 2018 it was put down to herbal leys of red clover and grass. In the USA and continental Europe, red clover is known to be a preferred dietary item of voles Microtus spp and has been associated with vole population increase. It is suggested that the increase in the viper population in the field margin may relate to a rise in the number of voles, which are an important component of the viper diet. Likewise, for grass snakes, small mammals may contribute 25 % or more of their diet. The use of herbal leys may present an important opportunity for the conservation of northern vipers in field margins and other adjacent habitats.
... One of the most important predators of anurans is the grass snake Natrix natrix (Gregory & Isaac, 2004). It is generally believed that this snake avoids eating adult yellowbellied toads (Bajger, 1980;Szymura & Pabijan, 2018), although it has been observed to consume their tadpoles and juveniles. ...
... d, h Higher magnification of c, g, respectively, showing Type II pores (pits) (arrowheads) on the Oberhäutchen. e: epidermis, d: dermis, m: muscle includes birds, mammals, reptiles and fish (Madsen 1983;Luiselli and Rugiero 1991;Filippi et al. 1996;Gregory and Isaac 2004;Luiselli et al. 2005;Šukalo et al. 2014). ...
Scale surface microstructure of reptiles are multifarious. There are macro- and micro-structural features such as sharp spines, leaf-like microornamentation and pores. However, the argument on whether they indicate taxonomic relationship or convergent evolution is still open as well as their effect on wettability or dirt shedding. Here we show a comparison of scale microstructure in closely related Natrix natrix and Natrix tessellata which differ in ecological niches. We found marginal denticulations on the distal boundary of the Oberhäutchen cells and two types of micropores; Type I covers the surface of Oberhäutchen cells and Type II covers the epidermal folds of hinge regions. Type I micropores are longitudinal grooves on dorsal scale surface while they are rounded on the surface of the gastrosteges. Type II are similar both inter and intra-specifically. Our results are in line with previous studies that indicated an inverse ratio between pore number and wettability. We found no qualitative significance in terms of microstructural features. Our findings support the hypothesis saying that microornamentation is indicator of phylogenetic relations. Yet, only a few models of scale surface microstructure which are shaped by the environmental conditions could have been generalized which indicates that Oberhäutchen cells as simple elementary morphological structures are highly plastic and species-specific studies can be considered as special cases. Apart from contribution to an old “nature-nurture controversy”, we anticipate our assay to be a comparative perspective of the multifunctional integument of widely distributed Natrix sp.
... We found a third peak in May for females, but associated with a small number of observations (n = 5). This reptile appears to have a foraging activity cycle similar to that observed in other European snake species, with a decrease of the feeding rate in midsummer and a subsequent increase in late summer/early autumn (Luiselli and Agrimi, 1991;Santos et al., 2000;Gregory and Isaac, 2004). The summer decrease is often associated with high temperatures (Luiselli and Agrimi, 1991;Santos et al., 2000) and, especially in viviparous species, with anorexia in gravid females in the second part of gestation (Brañ a et al., 1988;Luiselli and Agrimi, 1991). ...
ABSTRACT.—The Javelin Sand Boa, Eryx jaculus, is reported to be a predator of mammals, lizards and their eggs, and occasionally of birds and invertebrates, but data on its diet are scarce and fragmentary. Here we describe some aspects of the feeding behavior of E. jaculus on the Mediterranean island of Sicily. A total of 132 individual snakes were examined. Prey remains were found in 43% of them, both in their feces (82.5%) and gut contents (17.5%). The number of snakes observed and their feeding rate decreased in August, probably as a result of the relatively higher temperatures. Feeding rate increases were observed in adult females in September, perhaps to enhance body reserves before hibernation. The overall prey spectrum is dominated by small mammals, with a frequency of occurrence of 71.4%, but also consisted of lizard eggs (30.2%) and lizards (7.9%). Lizards seem to be occasional prey, and our frequent detection of ingested autotomized tails suggests E. jaculus has low efficiency as a saurian predator. We 0bserved a relationship between prey type and snout–vent length of the snakes. Lizard eggs are most frequently eaten by smaller snakes, which could be linked to gape size ontogenetic variation. We found differences in the prey spectrum between sexes and age classes. Our results indicate that juveniles, adult males, and females seem to adopt different foraging strategies. Females probably adopt ambush predation on small mammals, while juveniles are active foragers of lizard eggs. Adult males appear to be slightly more versatile predators, consuming both types of prey, probably because of their high mobility rates during the mating period.
RIASSUNTO.—Il Boa delle sabbie, Eryx jaculus, é noto come predatore di mammiferi, lucertole e loro uova e, occasionalmente, uccelli e invertebrati ma i dati sulla sua dieta sono scarsi e frammentari. In questo studio descriviamo alcuni aspetti del comportamento alimentare di E. jaculus in Sicilia. Abbiamo esaminato un totale di 132 individui, nel 43% di questi sono stati rinvenuti resti di prede nelle feci (82.5%) e nei contenuti stomacali (17.5%). Il numero di boa osservati e l’attività trofica sono diminuiti ad agosto, probabilmente a causa delle alte temperature. L’attività trofica delle femmine adulte è aumentata a settembre, presumibilmente per incrementare le riserve corporee prima dell’ibernazione. Lo spettro trofico complessivo comprende piccoli mammiferi, con una frequenza di comparsa del 71.4%, uova di lucertole (30.2%) e lucertole (7.9%). Queste ultime sembrano prede occasionali e l’ingestione frequente di code autotomizzate suggerisce una scarsa efficienza di E. jaculus come predatore di sauri. Abbiamo osservato una relazione fra il tipo di preda e la taglia dei serpenti. Le uova di lucertola sono più frequentemente ingerite dai serpenti più piccoli, questo potrebbe essere legato alla variazione ontogenetica dell’ampiezza orale. Sono state rilevate differenze nella composizione della dieta fra sessi e classi di età. I risultati indicano che i giovani e gli adulti dei due sessi sembrano adottare differenti strategie di foraggiamento. Le femmine sembrano nutrirsi esclusivamente di piccoli mammiferi che probabilmente predano in agguato, mentre i giovani sono prevalentemente ricercatori attivi di uova di lucertola. I maschi adulti appaiono leggermente più versatili rispetto alle femmine, includendo nella loro dieta entrambi i tipi di preda, forse a causa della loro maggiore mobilità durante il periodo degli accoppiamenti.
... Natricine snakes can opportunistically exploit seasonal aquatic habitats (e.g., temporary ponds; Seminara, Vagaggini, & Margaritora, 2008) that may lack structured riparian plant communities because of their high temporality. Moreover, N. astreptophora and N. helvetica are opportunistic terrestrial foragers (Gregory & Isaac, 2004;Salvador, 2014), and extend their use of terrestrial habitats beyond the riparian zone. These associations with riparian habitats can also show significant geographical variation, as these species occupy extensive ranges and extend into climatically diverse regions, including the pre-desert river valleys on the margins of the Sahara Desert (Kindler, Graciá, & Fritz, 2018;Schleich, Kästle, & Kabisch, 1996). ...
The influence of aquatic and riparian habitats on the composition of the local herpetofauna has not been studied extensively. We used redundancy analysis and multivariate ordination methods to evaluate the occurrence of semi‐aquatic reptiles in south‐eastern France, the Iberian Peninsula, and Morocco where the climate transitions from humid temperate to subtropical desert. All the semi‐aquatic reptile species present in this region were studied, including two native turtles (Emys orbicularis and Mauremys leprosa), three native snakes (Natrix astreptophora, N. helvetica, and N. maura), and one introduced turtle (Trachemys scripta). We hypothesized that these species will vary in their responses to differences in the composition of riparian habitats (vegetative community and relative proportion of trees, shrubs, grasses, water and bare ground surface) along the aridity gradient in the region. We found that the habitat niche marginality and niche breadth varied widely across species and climatic regions, although most of the species display a greater habitat niche breadth in the transitional semi‐arid belt. Mauremys leprosa and N. maura were the more generalist species, occupying a wide range of freshwater habitats, including streams associated with impoverished vegetation communities, characteristic of the arid southern Mediterranean region.
... Differences in head size and shape often result from selective pressure on dietary/ feeding niche separation, as they are usually accompanied by differences in average prey size, type, or both (e.g. Shine, 1986Shine, , 1991Shine, , 1993Houston & Shine, 1993;Forsman & Shine, 1997;Keogh, Branch & Shine, 2000;Shine et al., 2002;Gregory & Isaac, 2004;Vincent, Herrel & Irschick, 2004;Shine et al., 2012;Borczyk, 2015). The species in this study is one of the very few snake species that feed on fish eggs. ...
Background
Snakes exhibit sexual dimorphism in both head size and shape. Such differences are often attributed to different reproductive roles and feeding habits. We aim to investigate how sexual dimorphism is displayed in the highly specialised fish-egg-eating snake, Aipysurus eydouxii , by analysing two complementary features: body size and skull morphology.
Methods
We used data on body length, weight, and skull shape from 27 measurements of 116 males and females of A. eydouxii . We investigated both sexual dimorphism and allometric (multivariate and bi-variate) properties of skull growth in the analysed data set.
Results
We found that although there was female-biased sexual size dimorphism in body length, females were not heavier than males, contrary to what is commonly observed pattern among snakes. Moreover, females tend to possess relatively smaller heads than males. However, we only found very subtle differences in skull shape reflected in nasal width, mandibular fossa, quadrate crest and quadrate length.
Discussion
We suggest that the feeding specialisation in A. eydouxii does not allow for an increase in body thickness and the size of the head above a certain threshold. Our results may be interpreted as support for prey-size divergence as a factor driving skull dimorphism since such species in which the sexes do not differ in prey size also shows very subtle or no differences in skull morphology.
... Adult females and males were mainly observed foraging among boulders and stones, but never on willow branches. The grass snake is a generalist predator, feeding largely on various amphibians and, much less often, on other vertebrates (Gregory & Isaac, 2004) or invertebrates (consul, Eger & Kwet, 2009). Treefrog species (Hyla spp.) have been reported relatively rarely as prey for N. natrix but the Sardinian grass snakes (Natrix natrix cetti) is reported as an active hunter in water with the adults and tadpoles of Hyla sarda as their main prey (capula, rugiero & Luiselli, 1994). ...
... The grass snakes (Natrix natrix ) were used as our model predator. Grass snakes are active and generalist feeders, preying upon amphibians, fish, small mammals, reptiles and birds (Hailey & Davies, 1986;Gregory & Isaac, 2004;Consul et al., 2009). Grass snakes forage on newts mainly in their aquatic phase. ...
Organisms rarely experience a homogeneous environment. Rather, ecological and evolutionary dynamics unfold in spatially structured and fragmented landscapes, with dispersal as the central process linking these dynamics across spatial scales. Because dispersal is a multi-causal and highly plastic life-history trait, finding general drivers that are of importance across species is challenging but highly relevant for ecological forecasting.
We here tested whether two fundamental ecological forces and main determinants of local population dynamics, top-down and bottom-up control, generally explain dispersal in spatially structured communities. In a coordinated distributed experiment spanning a wide range of actively dispersing organisms, from protozoa to vertebrates, we show that bottom-up control, that is resource limitation, consistently increased dispersal. While top-down control, that is predation risk, was an equally important dispersal driver as bottom-up control, its effect depended on prey and predator space use and whether dispersal occurred on land, in water or in the air: species that routinely use more space than their predators showed increased dispersal in response to predation, specifically in aquatic environments. After establishing these general causes of dispersal, we used a metacommunity model to show that bottom-up and top-down control of dispersal has important consequences for local population fluctuations as well as cascading effects on regional metacommunity dynamics. Context-dependent dispersal reduced local population fluctuations and desynchronized dynamics between communities, two effects that increase population and community stability.
Our study provides unprecedented insights into the generality of the positive resource dependency of dispersal as well as a robust experimental test of current theory predicting that predator-induced dispersal is modulated by prey and predator space use. Our experimental and theoretical work highlights the critical importance of the multi-causal nature of dispersal as well as its cascading effects on regional community dynamics, which are specifically relevant to ecological forecasting.
... Although uncommon, fish predation is observed in some species including garter snakes, e.g. Thamnophis hammondi (Kennicott, 1860) (Bell & Haglund 1978), Agkistrodon piscivorus (Lacépéde, 1789) (Chiszar et al. 1986), Eunectes species (Miranda et al. 2017), Natricidae species (Cundall 1983, Gregory & Isaac 2004 and homalopsine snakes (Voris & Murphy 2002). These aquatic/semi-aquatic species either enter the water body to hunt and capture prey or predate animals adjacent to water sources (Cundall & Greene 2000). ...
... Furthermore, this method can only be implemented with species that have a large number of representative preserved specimens stored in museums. Another technique is to palpate wild specimens in the field and document regurgitated prey items and expelled faecal matter (Daltry et al., 1998;Gregory and Isaac, 2004). Like the previous method, this technique cannot detect temporal changes in diet beyond the time during which the study was carried out. ...
A total of 209 observations of Ahaetulla nasuta feeding on prey were compiled from social media platforms, citizen science websites, and from the literature in order to gain insights into the food habits of this arboreal colubrid, and to construct an inventory of the prey species recorded in its dietary spectrum. The diet of A. nasuta consists primarily of frogs (37.4%) and lizards (32.5%), occasionally snakes (19.9%), and rarely birds (9.22%) and mammals (0.97%). At least forty-four
species spanning 38 genera and 19 families have been recorded as prey items of A. nasuta; 41 of these trophic interactions are previously unpublished. These data serve as a preliminary exploration into the food habits of A. nasuta and can be used as a baseline for future hypothesis-driven research.
... It often escapes threats by entering the water, and may also dive into the stream and actively hunt for potential prey there. The snakes' swimming and predation behaviours disturb fine sediments on the bottom (Gregory and Isaac, 2004;Weiperth et al., 2014). Tadpoles of several amphibian species feed on the epibenthos, reduce the sediment layer on the surfaces of stones in streams, and modify the physical structure of the bottom (Flecker et al., 1999). ...
Elucidating the impact of faunal activity on stream channels is an emerging field wherein ecologists, fluvial geomorphologists, and engineers collaborate to research and manage fluvial ecosystems. Here, we focused on the geomorphological effects of animals in mountain streams. This ecosystem merits conservation measures as it furnishes cold-water refugia. We searched literature addressing the impact of various animal taxa on the river/stream bed structure. The citation sources were the Web of Science, Scopus, and ScienceDirect databases covering 1975–early 2020. We examined all animal taxa with documented or potential zoogeomorphological effects upon streams and assigned spatiotemporal scales to their impacts. Interpreting the literature was challenging due to a lack of uniformity in data treatment between species groups and over time. Though human interactions prevail in stream channels, animals also have a substantial effect on a spatial scale and their modifications are more durable. In general, animals markedly influence aquatic habitats. This literature compilation revealed much information about the geomorphological effects of beavers, redd-building fish, and large bottom-dwelling fish. The scale of impact of invertebrates such as crayfish or case-building caddisfly larvae on stony-gravel bottoms has previously been demonstrated. However, previous research has concentrated on only one taxon and has not demonstrated the bioaccumulation effect of multiple taxa. Quantitative data have been presented only for large terrestrial mammals crossing streams. There was comparatively little information on the impact of other terrestrial taxa on stream geomorphology. There were also few or no quantitative data on the impacts of aquatic fauna on mountain stream channels. Much has been reported about the effects of burying invertebrates but relatively little is known about the impacts of burying fish such as lamprey larvae. The present review highlights numerous outstanding information gaps. It is hoped that this review will facilitate ongoing zoogeomorphological research.
... Concerning MIHB, it is likely that the higher abundance of N. natrix in sites with high stem density of reeds can be explained by trophic reasons, as this species is essentially batracophagous (Gregory and Isaac 2004;Luiselli et al. 2005), and the density of frogs (Pelophylax ridibundus) at the study area was much higher in spots with high reed stem density than in more open spots (Luiselli et al., unpublished observations). It is also noteworthy that four N. natrix captured during this study regurgitated four adult P. ridibundus, indicating perhaps that this frog represents the bulk of the diet of this snake in the study area. ...
Reed bed ecosystems are crucial for the survival of complex animal communities in Europe and Western Asia, but have been subjected to considerable decline, especially in beds in eutrophic shallow lakes, throughout Europe during the last decades. In Western Asia, however, these ecosystems are still wide and in good ecological conditions, and they support highly biodiverse communities of species, including some highly threatened taxa. Here, we studied the spatio-temporal community dynamics of semi-aquatic reptiles in a wide reed bed biotope in Azerbaijan, and present conservation considerations for its optimal management for the survival of the authochtonous reptile species. Three reptile species (two snakes and one turtle) were found in the study area. Activity intensity was not even throughout the years, and was significantly more related to ambient temperatures in 2016 than in 2017. Interestingly, amphipod abundance was also significantly different between years, and correlated well with the differences in activity patterns observed in a turtle species. There were complex spatio-temporal patterns exhibited by the reptile species at the study area, with an excess of reptile individuals in the high density reed bed habitat during summertime whereas there was an excess of individuals in the open reed bed habitat in spring and autumn. This evidence suggests that there should be seasonal interhabitat movements of reptiles at the study area, and that the reed beds are not perceived as a homogeneous habitat type by reptiles. Several hypotheses are presented to explain the reasons behind these unexpected spatio-temporal patterns by reptiles in reed beds. Our study clearly shows that, in order to enhance the conservation of reptiles, it is important to keep a mosaic of areas with dense reed stands (high density of young stems) and of open reed stands (lower density of older stems), thus increasing habitat heterogeneity and favouring small-scale ecological key-structures.
... As a result, the grass snake is absent from many small islands, which often lack water sources (Broggi 2008(Broggi , 2009). However, it is well documented that N. natrix in arid islands, where the occurrence of amphibians is reduced, survives mainly feeding on lizards, geckos and small mammals (Schweizer 1935, Kratzer 1974, Gruber & Fuchs 1977, Cattaneo 1984, 1998, 2010b, Gregory & Isaac 2004, Luiselli et al. 2005. Natrix natrix is known to consume also poisonous prey like fire-bellied toads, Bombina sp. and fire salamander Salamandra salamandra (Maxinova et al. 2018). ...
The presence of the grass snake Natrix natrix (Linnaeus, 1758) (Squamata, Serpentes) is reported for the first time for the island of Kasos (Dodecanese, Greece).
... Although many salamander species develop defensive strategies (i.e., toxic secretions and cryptic and aposematic colorations) to deter predators, the consumption of salamanders by other vertebrates at higher trophic levels has been reported widely e.g., [69][70][71][72][73]. Salamanders provide food for birds and snakes e.g., [68,69,74]. For example, Preston and Johnson [67] found amphibians in most (93% of frequency of occurrence) of the studied aquatic gartersnakes (Thamnophis atratus) in California. ...
Many species of salamanders (newts and salamanders per se) have a pivotal role in energy flow pathways as they include individuals functioning as prey, competitors, and predators. Here, I synthesize historic and contemporary research on the reciprocal ecological role of salamanders as predators and prey in aquatic systems. Salamanders are a keystone in ecosystem functioning through a combination of top–down control, energy transfer, nutrient cycling processes, and carbon retention. The aquatic developmental stages of salamanders are able to feed on a wide variety of invertebrate prey captured close to the bottom as well as on small conspecifics (cannibalism) or other sympatric species, but can also consume terrestrial invertebrates on the water surface. This capacity to consume allochthonous resources (terrestrial invertebrates) highlights the key role of salamanders as couplers of terrestrial and aquatic ecosystems (i.e., aquatic–terrestrial linkages). Salamanders are also an important food resource for other vertebrates such as fish, snakes, and mammals, covering the energy demands of these species at higher trophic levels. This study emphasizes the ecological significance of salamanders in aquatic systems as central players in energy flow pathways, enabling energy mobility among trophic levels (i.e., vertical energy flow) and between freshwater and terrestrial habitats (i.e., lateral energy flow).
... La couleuvre à collier (grass snake en anglais) est une couleuvre très commune en Europe (Grimm et al. 2014). Il s'agit d'un serpent non venimeux des milieux humides et aquatiques qui se nourrit principalement d'amphibiens (Gregory and Isaac 2004). La taxonomie de cette espèce a été très récemment revue (Pokrant et al. 2016, Kindler et al. 2017 et le projet CIRFE s'est focalisé sur Natrix helvetica qui jusqu'à très récemment était considérée comme une sous-espèce de Natrix natrix (Kindler et al. 2017). ...
Scientific report presenting all the results obtained during the duration of the CIRFE project.
... These results were expected, since the frequency of specimens containing food items is usually low, ranging between 14 and 30% (MASCHIO et al. 2010). According to GREGORY & ISAAC (2004), this low frequency may be related to the period in which the specimen was collected. SHINE (1987) suggested that female snakes generally tend to reduce food consumption during their gestation period. ...
... With regard to Natrix natrix, our data revealed a predominantly piscivorous diet: 8 out of 9 prey items were fish (two Cyprinidae and six catfish) and only one was a green frog. This pattern does not mirror available data from other populations, where a generalist diet, with a prevalence of anurans, has been observed across the species' range (e.g., Gregory and Isaac, 2004;Luiselli et al., 2005;Corti et al., 2010). The reduced anurophagus behaviour of grass snakes locally may be caused by the interference exerted by the American bullfrog which, may prey not only on snakes, but also on native green frogs (Bissattini et al., 2018). ...
The presence of alien species can embody a form of disturbance for natural communities and the concomitant presence of alien species at different levels within the trophic chain may compromise ecosystem functionality. We studied the ecology of two species of snake (Natrix tessellata and N. natrix) in a system of five ponds with a high number of alien species at a Mediterranean area in central Italy. We evaluated the potential perturbations to ecological traits of snakes due to the presence of alien species, including their body size, population density, and food habits. We compared the studied populations' body size to that estimated in conspecific populations studied elsewhere, including populations at close distance from the study site. Distance sampling and Capture-Mark-Recapture techniques were used to calculate the population density. Diet was estimated using stomach contents and stable isotope ratios (δ 15 N and δ 13 C), using Bayesian stable isotope mixing models to estimate the contribution of food sources and species' isotopic niche spaces. Few prey items were found in the stomach contents of either species, with Ameiurus melas as the main prey. Based on isotope niche analyses, N. tessellata diet consisted of only alien species, and N. natrix diet mostly relied on alien species (> 80%). Stomach contents revealed high overlap between the two species, although isotopes showed a random resource use (i.e. low isotopic niche space overlap). Overall, we caught a low number of individuals, indicating small population sizes. Moreover, snakes at the study site were comparatively smaller in size than most other populations found in the literature and almost all the recorded individuals were in very poor condition or injured by ingested alien prey. We suggest that the presence of rich allodiversity has negatively affected the snakes' fitness by decreasing their foraging performance, increasing their risk of being preyed upon, or through other mechanisms.
... For the four species, we used 8 two-patch systems placed in a greenhouse with controlled temperature (16)(17)(18)(19)(20)(21)(22)(23)(24)(25) • C). Each system was made of two 130 L plastic containers (78 x 56 x 43 cm) connected by a circuitous plastic pipe (diameter: 10 cm, total length: 4.4 m) on the upper section of the container. ...
Ecology and evolution unfold in spatially structured communities, where dispersal links dynamics across scales. Because dispersal is multicausal, identifying general drivers remains challenging. In a coordinated distributed experiment spanning organisms from protozoa to vertebrates, we tested whether two fundamental determinants of local dynamics, top-down and bottom-up control, generally explain active dispersal. We show that both factors consistently increased emigration rates and use metacommunity modelling to highlight consequences on local and regional dynamics.
... Although habitat factors were not important influences on abundance of snakes at the regional scale, both species were more abundant in areas with higher proportions of various wet habitats. The connection of N. natrix with wet habitats is well known; such habitats are important for its main food resource -amphibians (Drobenkov, 1995;Gregory and Isaac, 2004). Mires and other wet habitats are regarded as typical for V. berus (Boshansky and Pishchelev, 1978;Phelps, 1978;Stumpel, 1992;Zuiderwijk et al., 1998), although not obligate (Belova, 1976). ...
The role of large-scale factors in influencing reptile abundances in temperate-zone lowland Europe is relatively obscure. Data on relative abundances of reptiles were collected in various regions of Latvia. Multiple regression analysis was used to determine the relationship between reptile abundance and climate and habitat predictors. For lizards, habitat was a more important regional-scale factor than climate, although warmth of summer was important in Lacerta agilis. For snakes, however, climate was a highly significant factor. Natrix natrix in Latvia is common only in areas with mild winter climate at elevations below 50 m a.s.l., while Vipera berus is frequent in upland areas with relatively harsh winters. Potentially, the latter species could be negatively affected by global warming.
... Additionally, our results indicate that releasing toxins by the Common Toad is ineffective in repelling the hedgehogs. Hedgehogs, like some snakes (e.g., Natrix natrix; Gregory and Isaac, 2004), may be able to digest toad toxins without being poisoned. Moreover, we repeatedly observed hedgehogs anointing their spines with the toad poison, a behavior that has been previously reported (Brodie, 1977;Crump, 2009). ...
European anurans are prey for a variety of predators, against which they have evolved a range of defense behaviors. We investigated defensive behaviors of three European anurans: the Common Toad (Bufo bufo), the Common Frog (Rana temporaria), and the Edible Frog (Pelophylax esculentus) during interactions with a predator (hedgehog) and a control stimulus (rabbit).We hypothesized that (H1) due to small capacity to flee quickly from a predator, B. bufo has evolved a more diverse repertoire of behavioral defenses than the ranids, R. temporaria and P. esculentus. We also hypothesized that (H2) B. bufo can minimize the secretion of metabolically costly poison through behavioral control. According to our predictions, the repertoire of defensive behaviors was more complex in B. bufo than in the ranids. Also, the number of threatening behaviors was higher in toads than in both frog species. Fleeing was the most common response employed by all tested anurans. We report a new anti-predator behavior in the Common Toad: head hitting. As B. bufo released
the poison only after squeezing of parotoid macroglands by the predator, we conclude that the Common Toad can minimize poison release through behavioral control. Our data suggest that length of hind-legs and, related to this, mode of locomotion (jumping vs. hopping) can affect anti-predator behavior in anurans.
... Grass snakes have round pupils reflecting their mainly diurnal lifestyle (although in the south of the range they may be more active at dusk or dawn during hot weather). Grass snakes are semi-aquatic and usually found foraging close to water (Fig. 3), where they prey on amphibians (i.e., frogs, toads, newts, tadpoles), and occasionally fish and small mammals (Arnold and Ovenden 2002;Gregory and Isaac 2004). Hatchlings prey on tadpoles and invertebrates (Arnold and Ovenden 2002) but are rarely seen feeding in the wild. ...
... As a result of field studies conducted in Northern Cyprus, the species is found to be fed on the animals like rodents, lizards, birds and snakes as indicated in literature. Recent studies on the feeding biology of snakes are mostly based on stomach contents of the species (Akani et al. 2003, Cobb 2004, Gregory & Isaac 2004, Babb et al. 2005, Çiçek & Mermer 2007, Barlow et al. 2009, Jablonski et al. 2015. The results of present study supports the findings of previous literature (Baran 1976, Abd Rabou 2007, Baier et al. 2009, Amr & Disi 2011, Lahony et al. 2013. ...
Dolichophis jugularis (L., 1758) is a common snake species in Cyprus. Previous studies reported that, D. jugularis mainly prey on rodents, snakes and lizard species. Our recent field studies, supported by photos of D. jugularis feeding is consistent with the results of previous studies. As a new species in the diet of D. jugularis we recorded Carduelis carduelis.
... Concerning amphibians, both frog species bred to a lesser extent in meadows with bushes. Open areas provide conditions unsuitable for grass snake (Natrix natrix) − a major predator of amphibians (Gregory & Isaac, 2004) − as well as for raccoon dog (Nyctereutes proconoides) − a generalist carnivore with a serious impact on amphibians and ground nesting birds (Sutor, Kauhala, & Ansorge, 2010). Table 2 The Spearman rank correlation coefficients (p-values in brackets) between landscape parameters and egg-clusters, and breeding success of moor frogs and common frogs. ...
Wet grasslands provide unique habitats for several taxa and offer multiple ecosystem services. Their degradation is therefore of increasing concern in many parts of the world. Baltic coastal meadows, which host diverse plant and bird communities and provide an essential breeding ground for amphibians, belong to the most threatened habitat types in Europe. In spite of the EU agri-environmental schemes, the threatened wader and toad populations, characteristic to these meadows, have not recovered, suggesting that the management efforts are failing to provide sufficiently high habitat quality for these species. In this paper we report the results of a large-scale survey determining the factors that influence the patterns of breeding habitat selection of four Charadriiform bird species on 24 coastal meadows in Estonia. We also examined whether the habitat conditions required by the threatened waders would benefit breeding amphibians and meadow plants and whether the threatened waders might act as focal species for managing coastal meadow biodiversity. In total, we analysed 23 landscape-variables, applying co-inertia analysis to discover common multivariate patterns in coastal meadow characteristics, breeding waders, plants and amphibians. We demonstrated that large (≥100 ha) and wide (mean width ≥200 m) meadows with extensive grazing, high water-table and no woody vegetation provide favourable breeding conditions for waders of conservation concern, but at the same time also support other Charadriiform birds, larger amphibian populations, and more diverse plant communities. Meadow management should therefore be targeted at threatened waders, especially Baltic dunlin, which could be considered as a focal species, and focus on the establishment of large and wide meadow areas with extensive grazing.
V poglavju Višje rastline smo uvodoma našteli najznamenitejše predstavnike flore območja celotnih Kamniško-Savinjskih Alp, med katerimi so nekatere endemične vrste, vrste na Rdečem seznamu ali pa so vrste zavarovane z Uredbo o zavarovanih prosto živečih rastlinskih vrstah oziroma z Direktivo o habitatih. Temeljito smo pregledali in predstavili izsledke preteklih botaničnih raziskovanj Kamniško-Savinjskih Alp. V sklopu projekta Rastlinstvo in živalstvo kalov v Kamniško-Savinjskih Alpah smo z metodo florističnega popisa na 151 kalih zabeležili 78 vrst višjih rastlin, ki so našteta v tabeli, zanimivejše med njimi pa smo tudi podrobneje opisali: kolenčasti lisičji rep, sivozelena sladika, bodičnati šaš, sivkasti šaš, avstrijska sita, bradavičasta sita, navadna vrelka, Scheuchzerjev munec, nitasto ločje, enostavni ježek, pritlikavi dristavec in močvirska vijolica. Nahajališča omenjenih vrst smo prikazali na zemljevidih.
"Bogato slikovno opremljeno poljudnoznanstveno delo šestih avtorjev ob strokovnem pregledu znanstvenikov in strokovnjakov v osmih poglavjih na svojih skoraj sto straneh približa izbor rastlinskih in živalskih vrst najširšemu občestvu ter predstavi biologijo višjih rastlin, mahov in jetrenjakov, kačjih pastirjev, dvoživk ter plazilcev. Ponudi nam pregled 151 kalov devetih raziskovalnih območij, za katere so navedene natančne najdbe, ki so tudi komentirane. Obenem so predstavljena še pretekla raziskovanja območja in dodani posamezni pripisi vrst." - Damjan Vinko, v spremnem nagovoru
The tessellated snake, Natrix tessellata, is one of the non-venomous oviparous snakes of Colubridae family, founded in northern Iran. This research was conducted in order to study of ecological conditions specially food habits and reproduction of this species. Sampling was done from April to November in Mazandaran province of Iran. Results showed that the spermatogenesis started in early June, maximize in August and September and ended in November. Spermatogenesis in this species is aestival and sperms are stored during winter for using in the next year. The oogenesis started in early June and ended in August. Fertilization was done in the first of summer especially end of June. Results showed that this species feeds on one frog and five fishes species including: Rana ridibunda, Hypophthalmichthys molitrix, Rhinogobius similis, Gambusia holbarki, Salmo trutta caspius ,Ctenopharyngodon idella Barbus capito, Carassius auratus, Capoeta capoeta and Cyprinus carpio. Also, food habits showed no differences between reproductive and non-reproductive seasons.
Diets of the terrestrial garter snake (Thamnophis elegans) and the common garter snake (T. sirtalis) were studied during seven consecutive summers at a lake in northern California, USA. The snakes were opportunities feeders; their diets varied dramatically from year to year, parallel with the abundance of prey. Snakes foraged more successfully, judging from the incidence of stomachs containing prey, in years when metamorphic toads (Bufo boreas) were available. Breeding failure in toads with associated with lowering lake level.
The aim of this chapter is to encourage additional studies of prey size-snake size relations. The fascinating evolutionary vistas sketched by Green (1983), Mushinsky (1987), Pough and Groves (1983), and Voris and Voris (1983) have not been explored as assiduously as they might. In this chapter I focus on one tantalizing result from the recent literature on snake diets in the hope of encouraging more work. The result is that in many of the snake species studied so far, larger snakes drop small prey items out of their diet. The implication is that snakes pass over, perhaps even avoid, some of the smallest prey items they encounter. Foraging theory is used to devise some hypotheses to explain this apparently enigmatic result. In trying to use foraging theory to this end, I was constantly plagued by the lack of relevant data. However, the lack of data is undoubtedly a reflection of our failure to adapt theory to snake biology. Perhaps even a provisional application of theory to the problem will help break the logjam.
The dramatic amphibian population declines reported worldwide likely have important ef- fects on their predators. In the Sierra Nevada, where amphibian declines are well documented and some are closely tied to the introduction of nonnative trout, the mountain garter snake, Thamnophis elegans elegans, preys predominately on amphibians. We surveyed 2103 high-elevation lakes in the Sierra Nevada, quantified the distributional relationship between the mountain garter snake and anuran amphibians (Pseudacris re- gilla, Rana muscosa ,a ndBufo spp.) and used this information to evaluate the possibility that amphibian declines lead to declines of garter snakes. We observed a strong association between amphibian presence and garter snake presence. The probability of finding snakes in lakes with amphibians was 30 times greater than in lakes without amphibians. Lakes with snakes had higher numbers of amphibians within 1 km (mean 5 4018.8) than did lakes without snakes (mean 5 642.1). On a landscape scale, in Kings Canyon National Park (where 40% of larger lakes contain nonnative trout) amphibians were found in 52% of lakes, and 62 garter snakes were found in 33 of the 1059 lakes surveyed. In contrast, in the John Muir Wilderness (JMW; where 80% of larger lakes contain nonnative trout), amphibians were found in 19% of lakes, and no snakes were found in any of the 1044 lakes surveyed. Based on these data, we suggest that the introduction of nonnative trout has led not only to the decline of amphibians but also to the decline of garter snakes. This study supports the hypothesis that the presence of amphibians is a prerequisite for garter snake per- sistence in high-elevation portions of the Sierra Nevada and that the introduction of trout into an ecosystem can have serious effects, not just on their prey but also on other predators in the ecosystem.
Island ecosystems are particularly vulnerable to exotic species. Here we show how an introduced prey has led to the wholesale restructuring of an island food web, including the near extinction of an endemic carnivore. Introduced pigs, by providing abundant food, enabled golden eagles to colonize the California Channel Islands. Eagles preyed heavily on the island fox, whose resulting decline toward extinction released populations of the competitively inferior island skunk. The presence of exotic pigs led to major ecosystem shifts by indirectly causing predation to replace competition as the dominant force shaping these island communities.
A five-year mark-recapture study at Sella Nevea, a montane (1100 m a.s.1.) site in the Carnic Alps, provided information on diets, growth rates, and reproductive output in an Italian population of the wide-ranging grass snake, Natrix natrix. Our snakes resembled a previously-studied population in lowland Sweden in terms of body size at sexual maturation in females (70 cm) and mean adult female body length (82 cm). However, growth rates were lower in our population, and sexual maturation was delayed (6–8 years, versus 4–5 years in Sweden), perhaps because of the cool climate and relatively brief growing period each year. Females produced a single clutch of 4–24 eggs in late July each year. Larger females produced larger clutches, but clutch size relative to maternal size was lower than in Swedish grass snakes. Hatchling sizes and Relative Clutch Masses (RCMs) did not shift with increasing female size. RCMs may provide a useful index of ‘costs of reproduction’ in this population, because females with high RCMs were very emaciated after oviposition, and hence may experience a greater risk of mortality, as well as a high energy expenditure. Prolonged incubation gave rise to longer, thinner hatchlings, but the low environmental temperatures at the study site may favour early hatching (and hence, result in a shorter fatter hatchling emerging from the egg, with more of its energy stores unused). Compared to sympatric viviparous snakes (Coronella austriaca and Vipera berus), the oviparous grass snakes can achieve a much higher reproductive output owing to a larger clutch size and more frequent reproduction (annual, rather than biennial or triennial). The abundant prey resource used by grass snakes (amphibians) may also enable them to recoup energy more rapidly after reproduction; dietary composition shifts ontogenetically in both sexes, with the largest prey (mice and adult toads) taken primarily by large female snakes.
Growth rate and age at sexual maturation in male and female grass snakes are examined. Females were found to grow faster, and to reach a larger size than males. Female fecundity was found to increase with size. Large size permits females to exploit both larger and also different prey species than males. Males reached maturity during their third year; females during their fourth or fifth year. The ecological significance of sexual size dimorphism and age at maturation are discussed. /// Исследованы скорость роста и возраст полового созревания у самцов и самок обыкновенного ужа. Установлено, что самки растут быстрее и достигают более крупных размеров, чем самцы. Плодовитость самок повышается с размерами. Большие размеры позволяют самкам использовать более крупные и иные виды жертв по сравнению с самцами. Самцы достигают половой зрелости на третий год; самки - в течение четвертого или пятого годов. Обсуждается экологическое значение размерного полового диморфизма и возраста достижения полового созревания.
Constraints on time and energy suggest that animals often will have to forgo one activity in favour of another. In the field, gravid garter snakes, Thamnophis elegans, eat little or nothing, especially late in pregnancy. In addition, they spend considerable time basking, presumably to aid development of their progeny. Apparently, therefore, a conflict exists between feeding and behaviours related to gestation. Alternatively, low feeding levels in the field might reflect reduced ability to catch food while gravid, or anorexia, attributable either to reduced space in the gut or to physiological suppression of appetite. In this study, by supplying abundant food in the laboratory, we test the hypothesis that gravid females are anorexic; we also examine the interactions among feeding, thermoregulation and reproductive condition. Typically, gravid females, whether fed or not, spent most of their time at the warm end of a gradient, as did fed non-gravid snakes; unfed non-gravid females spent significantly less time at the warm end. However, gravid snakes, even when presented with food ad libitum, ate less than non-gravid snakes, suggesting that they are anorexic while pregnant. Feeding and thermoregulatory behaviours of gravid females changed around the time of parturition (increased feeding, reduced warming rate). Comparable changes are seen in animals in the field, and are correlated with changes in movement pattern. Evidently, the tendency to eat little food is carried over into the laboratory, even when apparent proximate causes of the behaviour are removed. Although we cannot distinguish clearly between the two potential causes of anorexia, the evidence slightly favours physiological suppression of appetite. Physiological suppression of appetite while gravid would ensure that the urge to forage rather than thermoregulate does not diminish the chances of present reproductive success. By contrast, non-gravid snakes, faced with a shortage of food, lower their body temperature and reduce their metabolic costs.
In central Italy, water snakes of the genus Natrix (N. natrix and N. tessellate) are among the most abundant reptile species. We studied the feeding habits and food niche partitioning by these water snakes at a site located about 25 km north of Rome. The two species partially partitioned the available food sources. N. tessellata showed the highest specificity, feeding particularly on fish and almost exclusively on aquatic prey. N. natrix. on the contrary, preyed especially on amphibians but also on fish and terrestrial vertebrates. The coexistence of these snakes is similar to that reported among North American water snakes of the family Colubridae.
The prey spectrum of the Grass Snake, Natrix natrix (LINNAEUS, 1758), and Dice Snake, N. tessellata (LAURENTI, 1768) was studied in rich sympatric populations in the vicinity of a stream located in a hilly area of central Italy ('Rota', Tolfa mountains, about 150 m a.s.l., 42° 08' N, 12° 00' E). Both species were frequently present in the water of the stream or close to it. Grass Snakes were also found far from the stream, and preyed on a variety of small vertebrate species. Conversely, Dice Snakes were strictly bound to the water and its vicinity, and preyed almost exclusively on fish. Dice Snakes did not show significant ontogenetic changes in their dietary spectrum other than that larger individuals tended to feed on larger prey. Conversely, in the Grass Snakes, there was a remarkable ontogenetic change in diet composition, and larger females tended to prey frequently upon adult toads (Bufo bufo), while adult males frequently fed upon 'green frogs'. The toads were usually preyed at a distance far from the water (average dis- tance from the closest water body of a snake found with a toad in its stomach: 256.7 ±115.03 m, median: 233 m). About 91% of these toads were males. It is suggested that male toads were preyed more frequently than female toads because of their smaller size.
Closely related, sympatrtc species of organisms often show resource partitioning. In this study, diet partitioning is examined in three sympalric species of garter snakes (Thamnophis) on Vancouver Island. Thamnophis sirtalis feeds mainly on amphibians and earthworms, Thamnophis ordinoides on earthworms and slugs, and Thamnophis elegans on slugs, fish, and small mammals. Thamnophis sirtalis and T. ordinoides, which are mote widely distributed on Vancouver Island than is T. elegans, have not been shown to modify their diets in the absence of T. elegans, but it is suggested that this lack of niche shift may be due to variations in prey availability. Neither innate differences in food preferences among the species nor interspecific competition for food have been shown to explain the observed differences in diet among the three species. Certain types of prey appear more likely than others to turn up in large numbers in stomach samples and it is suggested that this may be due to variations in ease of capture and (or) abundance. Possible explanations of the observed diets are discussed.
Previous ecological studies of Thamnophis sirtalis in the Interlake region of Manitoba have concentrated on the spring and fall phases of the annual cycle. This study is an investigation of two aspects of the summer activity of these populations: summer dispersal and feeding habits. Summer dispersal in these animals is highly directional; snakes move south in spring and return north to their hibernation sites in late summer and fall. Large distances are also involved; movements of as much as 17.7 km have been recorded. No explanation of this pattern of dispersal is apparent. Feeding takes place in the summer range only, during June, July, and August. The wood frog (Rana sylvatica) is the most frequently eaten prey species. It is suggested that the short feeding period is the result of a life history strategy which maximizes the efficiency of reproductive activities at the expense of non-reproductive activities.
Diets of garter snakes (Thamnophis) often vary in space or time in response to variations in prey abundance. We compared the diet of the common garter snake (T. sirtalis) on Vancouver Island at fish-rearing facilities (hatcheries) and at nearby natural sites where fish were present but less abundant. Snakes of all sizes fed on fish at hatcheries, but fish were rarely eaten at natural sites, where amphibians or earthworms were the major prey types. Any particular characterization of the diet of this species therefore must be site specific. Although snakes exhibited intersite variation in diet, there was no evidence of temporal variation in diet at any site. The proportion of snakes with food in their stomachs varied among sites (perhaps indicating differences in frequency of feeding among sites) and was correlated with mean relative body mass of snakes. This suggests that some sites are more productive than others for snakes, but rigorous tests of whether snake populations are food-limited have not been done.
The prey and feeding frequency in free-living grass snakes was studied during 1993 and 1994 at a site in southern England. Individual snakes and common toads were recognized using PIT tags and a small number of adult snakes were radio-tracked over long periods to determine predation rates.
Grass snakes fed, almost exclusively, on common toads (adult, juvenile, and tadpoles). A positive correlation was found between prey size and snake size. Large snakes did not appear to prey upon small toads, although clearly capable of doing so.
Male and female snakes ate large meals (toads) approximately every 20 days between May and September, with females fasting for a period of about 45 days during gestation and egg-laying. After allowing for differences in the number and size of toads predated by male and female snakes, the mean amount of food consumed per day was estimated to be 2.3% and 1.6% of body weight.
Diets of the terrestrial garter snake (Thamnophis elegans) and the common garter snake (T. sirtalis) were studied at 22 sites in an area of about 250 km2 in northern California, during the summers of 1978–80. Overall, T. sirtalis consumed mostly amphibian and T. elegans ate an equal mixture of amphibians, fish, and leeches. However, this was more an effect of differential distribution of the two species among sites than of habitat partitioning within sites. Site was 5 times better as a predictor of diet than was species of snake. The relative frequency of T. sirtalis at the sites was correlated with the number of amphibian species.
Grass snake preys on Sand Lizard
- New Mcgraw-Hill
- York
- J Stanley
McGraw-Hill, New York. STANLEY, J. 1992/1993. Grass snake preys on Sand Lizard. British Herpetological Society Bulletin 42:29.
Ecology and Vagility of the Grass Snake, Natrix natrix helvetica Lacé
- J H Brown
- Chicago
- P R K Brown
- M Capula
- L Rugiero
- L And
- Luiselli
BROWN, J. H. 1995. Macroecology. Univ. of Chicago Press, Chicago. BROWN, P. R. 1991. Ecology and Vagility of the Grass Snake, Natrix natrix helvetica Lacé. Unpubl. Ph.D. diss., Univ. of Southampton, Southampton, U.K. CAPULA, M., L. RUGIERO, AND L. LUISELLI. 1994. Ecological observations on the Sardinian Grass Snake, Natrix natrix cetti. Amphibia-Reptilia 15: 221–227.
Amphibians and Reptiles—A Natural History of the British Herpe-tofauna Thermal ecology of Black Rat Snakes (Elaphe obso-leta) in a thermally challenging environment
- New Mcgraw-Hill
- York
- T Beebe
- R And
- Griffiths
- Harpercollins
- London
- G Blouin-Demers
- P J And
- Weatherhead
McGraw-Hill, New York. BEEBE, T., AND R. GRIFFITHS. 2000. Amphibians and Reptiles—A Natural History of the British Herpe-tofauna. HarperCollins, London. BLOUIN-DEMERS, G., AND P. J. WEATHERHEAD. 2001. Thermal ecology of Black Rat Snakes (Elaphe obso-leta) in a thermally challenging environment. Ecol-ogy 82:3025–3043.
The stomach contents of a Grass Snake, Natrix natrix, identified from skeletal re-mains
- C Gleed-Owen
GLEED-OWEN, C. 1994. The stomach contents of a Grass Snake, Natrix natrix, identified from skeletal re-mains. British Herpetological Society Bulletin 50:34–36.