DOI: 10.17026/dans-zmh-h9ah
title: Data from: Predation and survival in reintroduced populations of the Common hamster Cricetus cricetus in the Netherlands

description: We studied the survival Common hamster Cricetus cricetus in reintroduced populations (La Haye et al. 2020). The dataset contains information about observation intervals based on transmitter data collected during frequent visit to the studied populations.The study was performed in the southernmost part of the Netherlands, in the province of Limburg, in three areas: South (Amby-Heer-Sibbe; 50°50’18’’N, 5°48’32’’E), Centre (Sittard-Puth-Jabeek; 50°57’42’’N, 5°52’45’’E) and North (Koningsbosch; 51°02’41’’N, 5°57’35’’E), further referred to as areas 1, 2 and 3. These are typical agricultural landscapes: relatively open, with a mosaic of grassland, arable fields, small woods, little villages and small roads. Arable fields are approximately a few hectares in size and cereals are cultivated on 15-20% of all fields. Harvest of cereals starts at the beginning of July and continues till the first half of August.In the Netherlands the common hamster is found on arable land with loess or loamy soils, which is only present in Limburg and therefore restricting its range (Kuiters et al. 2010). In our study areas adaptive ‘hamster-friendly’ agricultural management has been established through the implementation of ‘hamster-friendly’ agri-environmental schemes (AES) on several hundreds of hectares. Hamster-friendly management implies cultivation of suitable crops on arable fields like cereals and alfalfa, in combination with harvest restrictions, giving hamsters the chance to survive and reproduce over a longer time period than on regular managed cereal and alfalfa fields (La Haye et al. 2014). This study on hamsters was strongly biased to arable fields with ‘hamster-friendly’ management, arable fields with an AES-scheme, and farmland nature reserves, because almost no hamsters live on regular managed agriculture fields anymore.TransmittersHamsters in the wild were trapped at the entrance of their burrow from approximately the end of March until the end of October, although trapping was minimal in June-August to prevent damage in standing crops. Hamsters trapped in the wild were brought to a wildlife veterinarian at Burgers Zoo (Arnhem, the Netherlands) for implanting a transmitter. For individual identification all trapped hamsters in the wild also received a pit tag. Normally a wild hamster was released at its burrow within 48 hours after being trapped.Each year about 25% of released captive-bred hamsters were operated to implant a radio transmitter. Implantation of a transmitter was at least five days before their release in the wild. Released captive-bred hamsters were one or two years old, depending on whether they had been used in the breeding program (La Haye et al. 2017). Implantation of transmitters in captive-bred hamsters was done by veterinarians at Blijdorp Zoo (Rotterdam, the Netherlands) and GaiaZOO (Kerkrade, the Netherlands).From 2002 to 2016 a total of 879 different common hamsters, wild and captive-bred, were equipped with a radio-transmitter and followed until their death or loss of the radio-signal. Hamsters that could not be monitored anymore as a result of a failing transmitter/low battery for more than 60 days before eventually being re-trapped alive, were, once re-trapped, treated in our analysis as being new individuals. This specific treatment of re-trapped hamsters is done to prevent overestimation of survival rates. Re-trapping hamsters after more than 60 days mainly happened in early spring directly after the hibernation period. During hibernation hamsters stay underground, which makes re-trapping literally impossible.It is not possible to exactly ascertain the age of a wild-born hamster, but only hamsters weighing at least 200 grams were equipped with a transmitter. We assumed that all trapped hamsters were therefore at least (sub)adults and capable of reproduction.Monitoring survivalAll hamsters with a transmitter were located once a week or once every two weeks during the active season, from mid March till mid October, and at least once in every two or three weeks during winter months (November till February). Each hamster was tracked at its burrow during daylight hours, after dawn and before sunset. Hamsters which could not be located during regular monitoring events, were searched for extensively around the last known location as soon as possible. Most of the missing hamsters or transmitters, were relocated within 500 meters from the last known location (van Wijk et al. 2011).Electric fences and spotlight hunting of foxesIn some areas and years enclosures were made with an electric fence around suitable fields to protect hamsters inside these enclosures. These enclosures excluded foxes and other large ground-dwelling predators like badgers and dogs, but enclosures were open for aerial predators and small mustelids (Kuiters et al. 2010; Villemey et al. 2013). The number of enclosures with an electric fence ranged from one to four per year and enclosures were randomly distributed over all areas, but with a mean of two enclosures per year. On average, these enclosures with an electric fence protected an area of two till three hectares.Regular daylight hunting of foxes was allowed in all years in all areas, but spotlight hunting during the nightly hours, after sunset and before sunrise, was only allowed with a special permit. The intensity of spotlight hunting therefore varied between years and areas. Spotlight hunting was intensified in the last four years of the project.hamsterdata.csvThe dataset contains 9083 records of intervals over which hamster survival is assessed. We explain each of the variables here:ID = individual identifier of the studied hamstersmale = sex of the hamster: 0 = female, 1 = maleyear = year of (the midpoint of) the observation intervalmidDay = midpoint of the observation interval, in day of the year (1 Jan = 1)isSummer = whether (1) or not (0) the midpoint of the interval was in summer (midDay&gt;74 & midDay&lt;289)days = length of the observation interval in daysarea = identity of the study area (1, 2 or 3)captiveBred = whether the hamster was captive bred (1) or wild (0)daySinceRelease = number of days since the release of the hamster (at the time of the midpoint)enclosure = whether (1) or not (0) the hamster was last observed within an enclosure with electric fencing (unknown in 1 case: NA)spotlight = whether (1) or not (0) spotlight hunting of foxes was allowed at the site and time of the observation intervalsurv = whether (1) or not (0) the hamster survived the observation interval; NAs signal the 238 cases in which we could not determine the fate of the hamsterReferencesKuiters L, La Haye M, Müskens G, van Kats R (2010) Perspectieven voor een duurzame bescherming van de hamster in Nederland. Rapport Alterra, WageningenLa Haye MJJ, Reiners TE, Raedts R, Verbist V, Koelewijn HP (2017) Genetic monitoring to evaluate reintroduction attempts of a highly endangered rodent. Conserv Genet 18:877–892La Haye MJJ, Swinnen KRR, Kuiters AT, Leirs H, Siepel H (2014) Modelling population dynamics of the common hamster (Cricetus cricetus): timing of harvest as a critical aspect in the conservation of a highly endangered rodent. Biol Conserv 180:53–61La Haye MJJ, van Kats RJM, Müskens GJDM, Hallmann CA, Jongejans E (2020) Predation and survival in reintroduced populations of the Common hamster Cricetus cricetus in the Netherlands. In preparationvan Wijk R, La Haye MJJ, van Kats RJM, Müskens GJDM (2011) Movement characteristics of the common hamster (Cricetus cricetus) in Limburg, the Netherlands. Säugetierkundliche Informationen Band 8, Heft 42, pp 79-92. Proceedings of the 16t and 17th Meeting of the International Hamster Workgroup; Ranis, Germany (2009), Gödöllö, HungaryVillemey A, Besnard A, Grandadam J, Eidenschenck J (2013) Testing restocking methods for an endangered species: Effects of predator exclusion and vegetation cover on common hamster (Cricetus cricetus) survival and reproduction. Biol Conserv 158:147–154