Action: Provide artificial nesting sites for raptors
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- Nine studies from North America and Spain found that raptors used artificial nesting platforms, although one describes low levels of use and another describes use increasing over time.
- Two studies from the USA describe increases in populations or population densities of raptors following the installation of artificial nesting platforms.
- Three studies describe successful use of platforms, whilst three describe lower productivity or failed nesting attempts, although these studies only describe a single nesting attempt each.
Many birds of prey return every year to the same nesting site, adding material so that the nest gets larger and larger. In extreme cases, this can damage the tree or structure that the nest is on, resulting in the nest falling. Providing platforms or other robust structures for birds to build on may, therefore, help to increase reproductive success.
Supporting evidence from individual studies
A before-and-after study at a marshland site in Maryland, USA (Rhodes 1972), found that the number of osprey Pandion haliaetus nests at the site increased from 4-6 before 1968 to 22 in 1971, and chick production tripled, following the erection of 24 artificial nesting platforms in 1968-72. Platforms had an 82% occupancy rate (59 nesting attempts out of 72 available nest-years) and more nests were found on platforms than at natural nest sites (59 nesting attempts on platforms vs. 12 at other sites). Nests on platforms produced an average of 1.3 chicks/nest, whilst natural nests produced 1.8 chicks/nest. Platforms consisted of a 122 x 122 cm platform of planks and wire on a 6.1 m wooden pole. The platform was braced, sunk 150 cm into the ground and designed to withstand hurricane-force winds.
A small study in 1976-9 in three scrub and grassland habitats in Idaho, USA (Howard & Hilliard 1980), found that ferruginous hawks Buteo regalis nested on 24 nesting platforms provided in 1976, with one attempt in 1977 and three attempts in both 1978 and 1979. An average of 1.7 chicks/nest fledged. Platforms were provided in shaded/un-shaded pairs, and hawks only used unshaded platforms, with one pair moving platforms when the shade was moved to the platform they had used. This study also discusses platform use by common ravens Corvus corax, discussed in ‘Provide artificial nest sites for songbirds’.
A small study at a reservoir in Arizona, USA (Grubb 1983), found that a bald eagle Haliaeetus leucocephalus pair used an artificial nesting structure in the breeding season of 1978-9, but failed to fledge any chicks. The structure consisted of a tripod of aluminium pipes supporting an existing nest which had failed in 1976 (when it fell in the water) and 1977 (when it was blown down in high winds). The nest was thought to have failed due to thin egg shells.
A controlled before-and-after study over nine years in two pastoral sites in Canada (Schmutz et al. 1984) found that the breeding density of ferruginous hawks Buteo regalis increased following the provision of 98 nesting platforms in 1975 in an experimental area (nine nests in 1975 vs. 14 in 1983, increased populations in all five subareas). There was no increase in a control area, without platforms. Swainson’s hawk B. swainsoni populations also increased from 0.1 pairs/km2 in 1975 to 0.15 pairs/km2 in 1983, but there were no differences between experimental and control areas. Less than 40% of hawk populations used platforms for the first two years, but use increased with time. Platforms were either 120 x 60 x 20 cm wooden boxes, or wire baskets, 60-90 cm in diameter and 20 cm deep. Both were lined with shrubs or grasses and mounted on wooden poles, buried 60-90 cm in the ground. After 17 ploes fell, the authors recommended burying them deeper. Platforms provided with shade were used more than un-shaded ones.
A small study at a lake in Saskatchewan, Canada (Bortolotti et al. 1988), found that one out of two artificial nesting platforms were used by bald eagles Haliaeetus leucocephalus. The platforms were erected in 1980 and a nest was built in 1986, although no chicks fledged from it.
A replicated study in 1978-90 at a lake in Saskatchewan, Canada (Houston & Scott 1992), found that osprey Pandion haliaetus pairs fledged significantly more chicks from nests built on artificial platforms than from those in trees (1.3 chicks/breeding attempt for 70 attempts on platforms vs. 0.9 chicks/attempt for 205 attempts in trees). This difference was due to higher success rates on platforms (63% of 70 attempts on platforms vs. 46% of 205 attempts in trees), with no significant differences between productivities of successful nests (2.1 chicks/nest for 44 successful attempts on platforms vs. 2.0 chicks/nest for 94 successful attempts in trees). Nests were erected between 1978 and 1985 (ten platforms, 33% usage) and 1986-1990 (ten nests, 95% usage) and were made of wood.
A small study in Florida, USA (Marion et al. 1992), found that a bald eagle Haliaeetus leucocephalus pair successfully used a nest on an artificial platform built in June 1989. The pair fledged two chicks from the nest on the platform in 1990 and attempted nesting again in 1991, although the second attempt was disrupted by heavy traffic below the platform and was not successful. The platform was made of plywood, measured 1.5 x 1.5 m and was erected on a power pylon, <1.5 m to the site of several unsuccessful nesting attempts. A nest of loblolly pine Pinus taeda branches was also provided on the platform.
A replicated study reviewing an osprey Pandion haliaetus translocation programme in an urban area of Minnesota, USA (Martell et al. 2002), found that all but three of 26 nest sites used by 143 translocated ospreys and their young were artificial nesting platforms provided for the birds. Of these, 20 nests were productive, with only one not being situated on a nesting platform. This study is discussed in more detail in ‘Translocate individuals’.
A small study at a reservoir in southern Spain in 2005 (Muriel et al. 2006) found that a pair of ospreys Pandion haliaetus successfully raised two chicks that were fostered to them in a nest on an artificial nesting platform. This study is discussed in more detail in ‘Foster eggs or chicks with wild conspecifics’.
- Rhodes L.I. (1972) Success of Osprey Nest Structures at Martin National Wildlife Refuge. The Journal of Wildlife Management, 36, 1296-1299
- Howard R.P. & Hilliard M. (1980) Artificial nest structures and grassland raptors. Raptor Research, 14, 41-45
- Grubb T.G. (1983) Bald eagle activity at an artificial nest structure in Arizona. Raptor Research, 17, 114-121
- Schmutz J.K., Fyfe R.W., Moore D.A. & Smith A.R. (1984) Artificial nests for ferruginous and Swainson's hawks. The Journal of Wildlife Management, 48, 1009-1013
- Bortolotti G.R., Dzus E.H. & Gerrard J.M. (1988) Bald eagle nest on an artificial tree-top platform. Journal of Raptor Research, 22, 66-67
- Houston C.S. & Scott F. (1992) The effect of man-made platforms on Osprey reproduction at Loon Lake, Saskatchewan. Journal of Raptor Research, 26, 152-158
- Marion W., Quincy P., Cutlip C. & Wilcox J. (1992) Bald eagles use artificial nest platform in Florida. Journal of Raptor Research, 26, 226
- Martell M.S., Englund J.V. & Tordoff H.B. (2002) An urban osprey population established by translocation. Journal of Raptor Research, 36, 91-96
- Muriel R., Ferrer M., Casado E. & Schmidt D. (2006) First breeding success of osprey (Pandion haliaetus) in mainland spain since 1981 using cross-fostering. Journal of Rapto Research, 40, 303-304