Habitat Preferences for the Corn Crake (Crex crex) in Sweden Erik Andersson Degree project in biology, Master of science (2 years), 2009 Examensarbete i biologi 30 hp till masterexamen, 2009 Biology Education Centre and Biology Education Centre, Department of Population Biology, Uppsala University Supervisor: Jacob Höglund Table of contents Abstract ...................................................................................................................................... 2 Sammanfattning ......................................................................................................................... 3 Introduction ................................................................................................................................ 4 History .................................................................................................................................... 4 Biology and Ecology ................................................................................................................ 4 Population status.................................................................................................................... 5 Method ....................................................................................................................................... 6 Results ........................................................................................................................................ 7 Vegetation type ...................................................................................................................... 7 Moist condition ...................................................................................................................... 8 Vegetation height ................................................................................................................... 8 Distance to water ................................................................................................................... 9 Multiple logistic regression .................................................................................................... 9 Discussion ................................................................................................................................. 10 Vegetation type .................................................................................................................... 10 Moist condition .................................................................................................................... 11 Distance to water ................................................................................................................. 11 Conservation actions ............................................................................................................ 11 Acknowledgments .................................................................................................................... 12 References ................................................................................................................................ 12 Appendix ................................................................................................................................... 14 1 Abstract The Corn crake (Crex crex) is a bird within the rail family that have during the second half of the 20th century suffered a major decline in numbers, not only in Sweden but in Europe as well and is classified vulnerable (VU) by the Swedish red list and near threatened (NT) by the IUNC red list 2008. From being a common bird in Sweden during the 18th and the 19th century with an estimated population size of 60 000 pairs the population today is believed to only consist of 250 ‐1000 individuals. The most important factor behind the decline is the agricultural revolution that took place between 1910‐1940 across most parts of Europe. Instead of as previously using hand held tools on small meadow patches, machines were now introduced and the meadows were drained and combined which led to big habitat losses all over Europe. This forced the Corn crake out onto more dangerous areas such as hay and silage meadows where the bird easily became victim to the fast going grass mowing machines. To learn more of which kind of habitat the Corn crake prefers in a present day agricultural landscape in central Sweden an inventory was done where 27 locations with Corn crakes were identified as well as 27 places without. Analyses of the various factors that were collected at each location indicate that the most important feature when it comes to habitat choice is the vegetation height followed by the vegetation type. Whether the area is wet or dry seemed to be of importance as well but there were no significance with distance to water. 2 Sammanfattning Kornknarren (Crex crex) är en fågel inom rallfamiljen som under den senare delen av 1900‐ talet genomgått en drastisk minskning i antal individer, inte bara i Sverige utan även i stora delar av Europa. Den är idag klassad som hotad (VU) enligt den svenska rödlistan och missgynnad (NT) enligt IUNC’s rödlista 2008. Från att ha varit en vanlig fågel under 1700‐ 1800 talet med en beräknad populationsstorlek upp mot 60 000 par så har antalet sjunkit till dagens 250‐1000 individer. Den största anledningen bakom minskningen tros vara den revolution inom lantbruket som skedde mellan 1910‐1940 över större delen av Europa. Istället för handredskap och små ängar så började man nu använda sig av maskiner samt dränera de tidigare små ängarna för att få större, vilket innebar habitatförluster för kornknarren. Arten blev nu tvungen att söka sig till farligare platser såsom hö och ensilageängar där fågeln lät föll offer för de snabbgående slåtterkrossarna. För att undersöka vilken typ av habitat som kornknarren föredrar i ett modernt jordbrukslandskap i centrala Sverige så utfördes en inventering där 27 platser med kornknarr identifierades samt 27 platser där den saknades. Analyser av en rad olika faktorer som noterades vid varje plats tyder på att vegetationshöjden följt av vegetationstyp är de viktigaste faktorerna när det kommer till att välja habitat. Mindre viktigt var det om området var fuktigt eller ej samt om det var nära till vatten. 3 Introduction History During the latter half of the 20th century the agricultural landscape in Sweden went through a drastic change. The old standard, where most of the work was done by man and animal on a small scale disappeared. Instead machines were introduced which led to more efficient farming methods and the small fields were drained and enlarged (Berg & Pettersson 2007). This revolution occurred not only in Sweden but in most parts of Western Europe as well and it had a strong negative impact on the birdlife connected to the agricultural environment. According to Fuller et al. (1995), who did a comparison between two atlases from 1970 and 1990 in England, 24 of 28 farmland bird species have had their distribution range reduced and 15 of 18 species had suffered a population decline. No such survey has ever been done in Sweden but 46 % of the animals on the Swedish Red List are connected to farmland areas and 15 % of these are farmland birds which give an indication that there has been a similar downfall in Sweden. The Corn crake (Crex crex) is a farmland bird that often could be heard on the fields and meadows in the beginning of the 20th century (Pettersson 2007). Due to the change in agricultural management many of these areas disappeared and this has forced the Corn crake to more dangerous areas such as; grasslands that are managed for hay and silage and crop fields (Green et al. 1997) These are mainly agricultural areas with a lot of disturbances and a high risk of being killed by machines during the hay season. According to Crockford et al. (1998) there has been a 20 ‐ 50 % decline in Corn crake numbers during the last 20 years across Europe. Since the Corn crake is well known among farmers and the general public as an indicator of a healthy farmland landscape its value is highly regarded and much research is done to save it. Biology and Ecology The Corn crake belongs to the Rallidae family and can reach a length of 27‐30 cm and weigh between 140‐200 g. It is smaller in body size compared to the more common water rail (Rallus aquaticus) and has light brown wings and red‐brown legs (Ulfstrand 2003). The male has a very distinct song (sounding like “errp‐errp”) which can be heard from a distance of up to one kilometer and can continue for several hours during the night (Pettersson 2007). The song can also be heard during other hours but then in a less frequent manner (Green et. al 1997). The female on the other hand only makes a few sporadic, almost silent calls; instead it spends its time hiding in tall vegetation (Tyler & Green 1996). In Sweden, predators are not considered to affect the populations particularly much. However, in very local areas a Corn crake can be eaten by a mink or a cat but it is not considered common (Pettersson 2007). The Corn crake is an omnivorous bird and their diet varies. During the breeding season the birds feeds off of many different invertebrates that are found on the ground or on plants (Ulfstrand 2003) but it has been recorded to eat small fish and amphibians as well (Green et al 2007). The diet also seems to differ geographically. In Poland the Corn crake mainly lives of insects whereas in Scotland and Ireland it prefers mollusks and earthworms. The prey of Corn crakes can be found in high abundances in other areas