Action: Provide artificial nesting sites for divers/loons
- A replicated before-and-after study from the UK found that there was a very large increase in loon productivity on lakes provided with nesting rafts, with a corresponding increase in productivity across the whole country.
- Two studies from the USA found higher nesting success on lakes with floating nesting rafts, compared to sites without rafts, but no new territories were established on lakes without loons but with rafts.
- A replicated study from the UK found that loons used nesting rafts and artificial islands in some areas of the UK, but not others.
Divers or loons (Gaviidae) are specialised for swimming and diving and cannot move quickly on land. This means they are vulnerable to predators and frequently nest on small islands and patches of vegetation. Providing these habitats where they are absent may increase the number of birds using a site, increase their reproductive success, or allow the colonisation of new lakes.
Supporting evidence from individual studies
A small before-and-after study at two small lakes in Minnesota, USA (McIntyre & Mathisen 1977), found that common loons (great northern divers) Gavia immer used floating nesting platforms in 83% of breeding attempts in 1970-3, following their installation in 1970. Nesting success was 67%, compared with 60% for loons on four lakes with natural islands and older platforms (the number of nesting attempts is not given). However, no new territories were established at three additional lakes without loons after platforms were installed in 1970. Platforms were made from sedge mats and logs and anchored with concrete blocks between 3 m and several hundred metres from shore.
A 1992 replicated study of the use of artificial islands and floating platforms at 17 wetland nature reserves across the UK (Burgess & Hirons 1992) found that red-throated loons (divers) Gavia stellata and arctic loons (black-throated divers) G. arctica used both well-vegetated and bare shingle-covered islands and platforms at inland sites (i.e. on lakes and lochs) in Scotland. However, neither species used islands or rafts at Scottish coastal sites, or any sites in England or Wales. The review also examines island and platform use by grebes, rails, ground-nesting seabirds, waders and wildfowl.
A replicated before-and-after trial on lochs in Scotland between 1980 and 1997 (Hancock 2000) found that installing 63 nesting rafts in arctic loon (black-throated diver) Gavia arctica territories in 1992-5 increased chick productivity of the British population by an estimated 44% (from approximately 0.24 large chicks/territory to 0.35 large chicks/territory, 60-100 territories monitored each year), with an estimated 170% increase in the 44 territories where rafts were used (representing approximately 25% of the British population). Rafts consisted of a 3.6 x 2.4 m polystyrene rectangle with sides sloped to allow access from the water. They were covered in hessian, netting and turf and anchored to concrete blocks in shallow (1-3 m) water close to natural nest sites known to be susceptible to flooding and hidden from public roads to avoid illegal egg collecting. Rafts lasted at least ten years with annual maintenance.
A replicated, controlled trial at 52 lakes in Wisconsin, USA, in 1996-8 (Piper et al. 2002), found that common loons (great northern divers) Gavia immer had significantly higher hatching and fledging success in 26 lakes provided with nesting platforms, compared to 26 control lakes, without platforms (83% of clutches incubated until hatching date and 0.74 chicks fledged/clutch for 23 clutches on platforms vs. 49% of 41 clutches incubated and 0.56 chicks fledged/clutch for 59 clutches on natural sites). Increases were found across all lakes, irrespective of previous productivities. Rate of platform use increased each year, from 15% in 1996 to 50% in 1998 and was high across all lake qualities. Platforms were 1 m2 and made from Styrofoam blocks surrounded by logs and covered in soil and moist vegetation. They were anchored in water 0.5-5 m deep and 6-15 m from shore, inside existing territories.
- McIntyre J.W. & Mathisen J.E. (1977) Artificial islands as nest sites for common loons. The Journal of Wildlife Management, 41, 317-319
- Burgess N.D. & Hirons G.J.M. (1992) Creation and management of artificial nesting sites for wetland birds. Journal of Environmental Management, 34, 285-295
- Hancock M. (2000) Artificial floating islands for nesting black-throated divers Gavia arctica in Scotland: construction, use and effect on breeding success. Bird Study, 47, 165-175
- Piper W.H., Meyer M.W., Klich M., Tischler K.B. & Dolsen A. (2002) Floating platforms increase the reproductive success of common loons. Biological Conservation, 104, 199-203