Action: Use perches to increase foraging success
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- Two studies from the USA found that raptors and other birds used perches provided, whilst a replicated and controlled study in Sweden found that raptors used clearcuts with perches significantly more than those without.
- However, a controlled study from the USA found that overall bird abundances were not higher in areas provided with perches and a small controlled cross-over trial on an island in the USA found that San Clemente loggerhead shrikes Lanius ludovicianus mearnsi did not alter their hunting patterns or increase their success rates following the installation of perches in their territories.
If prey are plentiful but birds have low hunting success then it may be possible to increase population sizes by making hunting more effective, for example by providing perches for birds to use.
Supporting evidence from individual studies
A controlled study in June-July 1979 in tallgrass prairie at Konza Prairie Research Natural Area, Kansas, USA (Knodel-Montz 1981), found that bird densities in unburned prairie sites were no higher in areas provided with artificial perches than in areas without perches (31 males of all species/ha in both areas). Numbers were higher in a burned area with perches (56 males/ha vs. 27) but not when dickcissel Spiza americana and red-winged blackbird Agelaius phoeniceus (attracted to a stream in the former area) were excluded. Twenty three perches (1.5 and 2 m long wooden stakes) were added to a 35-ha area of annually burned prairie and 17 to an adjacent 25-ha unburned area. A 12-ha area of burnt and a 39 ha unburnt prairie with no artificial perches served as controls. Eight species used 48% of perches in the burned area, compared with 29% used by four species in the unburned area.
A replicated trial in shrubland on Rhode Island, USA, in winter 1978-9 (Reinert 1984), found that ten raptor species appeared to make frequent use of 14 dead trees erected in 1977, whilst four species used nine man-made perches. In total, raptors were seen using the perches 525 times over 120 days, with most using the perches for resting and American kestrels Falco sparverius also using them for hunting and eating.
A replicated, controlled experiment in central Sweden (Widén 1994) found that raptors used clearcuts with perches significantly more than those without (49 raptor observations in clearcuts with perches vs. 16 in those without). In the 1986 post-breeding season, 11 clearcuts (3.7-19.9 ha) were provided with 6 m high, regularly-spaced, perches (2/ha), and 11 had no artificial perches. Natural perches were virtually absent. Raptor use of the clearcuts was recorded April-May in 1987-1988. In autumn 1987, perches were switched between areas. In total, 33 raptor observations were made in 1987 and 32 in 1988; 85% (55) were common buzzard Buteo buteo, 14% (9) common kestrel Falco tinnunculus plus one hen harrier Circus cyaneus.
A small controlled cross-over trial in shrubland and grassland on San Clemente Island, California, USA (Lynn et al. 2006), found that four pairs of San Clemente loggerhead shrikes Lanius ludovicianus mearnsi did not alter their hunting behaviour or success rate following the installation of 15 perches in their territories (approximately 50-75% success with perches vs. 60-65% without). However, some pairs did shift their hunting areas to include perches, suggesting that perches have the potential to increase the area of the island suitable for shrikes.
- Knodel-Montz J.J. (1981) Use of artificial perches on burned and unburned tallgrass prairie. Wilson Bulletin, 93, 547-548
- Reinert S.E. (1984) Use of introduced perches by raptors: experimental results and management implications. Raptor Research, 18, 25-29
- Widén P. (1994) Habitat quality for raptors: a field experiment. Journal of Avian Biology, 25, 219-223
- Lynn S., Martin J.A. & Garcelon D.K. (2006) Can supplemental foraging perches enhance habitat for endangered San Clemente loggerhead shrikes? Wilson Journal of Ornithology, 118, 333-340