Habitat associations of nightjars breeding on heathland in England
The British nightjar population declined throughout much of the 20th century, due mainly to loss of heathland, the nightjar's traditional breeding habitat. The population has increased in numbers in recent decades. However, this increase has not been uniform across the range, and the breeding range itself has shown only marginal recovery during the period of population increase. This project used data from the last national survey, plus various habitat datasets, to analyse habitat associations of nightjar on heathland in England. These analyses are intended to help inform heathland restoration for nightjar.
- To analyse habitat associations of nightjar on heathland in England.
Work planned or underway
Project completed in October 2007.
Nightjars were present on 327 heathland patches in England during the 2004/05 survey. These ranged in size from 0.2 ha to 2 874 ha, or 28.7 km2 (mean = 1.1 km2, S.D. = 2.9 km2), although 100 patches (31 %) were smaller than 0.1 km2 and 261 (81 %) smaller than 1 km2 in size. The number of nightjar breeding territories on these patches ranged from 1 to 105 (mean = 4.8, S.D. = 9.9), but 159 patches (49 %) contained just one nightjar territory, and 288 (88 %) contained ten or fewer. The minimum size containing more than one nightjar territory was 1.5 ha. The median density of nightjars on the heathland patches was 9.8 males per km2.
The effects of habitat fragmentation were investigated, in terms of patch size and isolation, and were found to affect both occupancy of patches and densities on occupied patches. Occupied patches were significantly larger than unoccupied patches. The likelihood of a patch being occupied increased with increasing area of heathland in the vicinity (area within 10 km, excluding the area of the patch itself). There was also an effect of number of heathland patches within 10 km, but this was dependent upon the area effect. For patches with a smaller amount of heathland in the vicinity, it was better for this to be in a larger number of patches. It is suggested this could be due either to correlation with area of heathland within 10 km, or increased dispersal ability through a 'stepping stone' effect. For patches with a larger area of heathland in the vicinity, likelihood of occupancy was increased where the heathland was in fewer, i.e. larger, patches. Nightjar density increased with increasing connectivity to other patches, particularly occupied patches. Overall, 40 % of the occupied heathland patches were less than 100 m, and 86 % less than 500 m, from the nearest other occupied patch. There was a weak effect of decreasing density with increasing patch size. However, the average size of heathland patch in England is 0.17 km2, and the average size of a patch occupied by nightjars is 1.06 km2, thus heathland restoration for nightjars should be aimed at increasing mean patch size.
The results support the current approach of recreating heathland close to other heathland and populations of nightjar, increasing mean Patch size, and reducing the isolation of existing patches where they are fragmented. In areas with less heathland, the creation of 'stepping stones' of suitable habitat to facilitate dispersal between patches may be beneficial, where it is possible to join patches.
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