KOFFIJBERG K, KLEUNEN A VAN & MAJOOR F (2007) Territorial behaviour and habitat use of Corncrakes Crex crex in the Netherlands revealed by radio-tracking. LIMOSA 80 (4): 167-171.

During May-August 2007, 24 radio-tagged male Corncrakes were studied in floodplain meadows of the rivers IJssel and Zwarte Water, near Zwolle, Overijssel, the Netherlands. This is one of the core breeding areas within the country (54 singing males recorded in 2007) and conservation measures for Corncrakes (delay of mowing until 1 August, mowing inside-out) have been carried out here from 1998 onwards. The radiotelemetry study aimed to assess the impact ofmowing, in order to evaluate conservation measures taken in the framework of the national action plan. As radiotracking of Corncrakes had not been conducted before in the Netherlands, the study also revealed several aspects of territorial behaviour and habitat use in Dutch Corncrakes. Birds were trapped and fitted with radio-transmitters (2.5 g Holohil tags) between 30 May and 19 July. They were tracked for a period of on average 3 weeks (maximum 6-7 weeks), mostly during daytime (only two nocturnal checks were conducted). During fieldwork, the entire study area was searched for all active radio-tags and birds were located with a precision of c. 5 m.
      A comparison of singing activity and presence of radiotagged males (for presumed same individuals) revealed that many birds were still present after singing had ceased (Fig. 1). This corresponds to findings from other studies that indicate that Corncrake males stop singing as soon as they are accompanied by a female, and resume singing after the pair-bond for the first brood has broken up. Moreover, it fits rather well in an earlier study of singing activity in the northern Netherlands, showing a bimodal pattern in the number of singing males and their singing intensity throughout the season, probably representing the two broods (Fig. 2).
      Of all 154 localisations, 47% were positioned within 100mof the singing site of themale, the distance that is used as the radius of the area in which mowing is delayed. Hence, this 100 m radius might still pose a high risk of disturbance during mowing and 250 m, as e.g. used in conservation schemes in the British Isles, might be a better alternative (78% of all localisations fell within this range). Males did show movements around their singing site during daytime and in 15 out of the 24 tagged individuals, overlap in home range was considerable (Fig. 3). Home range sizes calculated from our study are exceptionally small compared with earlier studies, especially those from Ireland and Scotland (Tab. 1), even if taking into account that we probably underestimated home ranges due to the low tracking frequency. Causes of these differences could be (1) variation in food availability, (2) the narrow floodplains in our study area compared to some areas abroad, or (3) different territorial behaviour (due to the small floodplains, males tend to move over longer distances, i.e. out of the area, between broods). Due to such differences, care should be taken in extrapolating results from the few well-known Corncrake studies of Tyler and Schäffer to other parts of the breeding range.

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