Action: Use artificial nests that discourage predation
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- Three trials in North America found lower predation or higher nesting success of wildfowl in nest boxes or nesting ‘tubs’ than natural nests in tree cavities or on the ground.
- A trial in captivity found that raccoons could be prevented from entering nest boxes if they were topped with a metal cone with a 7.6 cm overhang and the distance between entrance hole and the roof was increased from 30 to 60 cm.
- A replicated study in the USA found that fewer woods duck Aix sponsa used nest boxes with predator guards on when given the choice of unaltered boxes, but that both designs were used with equal frequency when only one design was available.
Nest boxes are distinctive and often easier to see than natural nests. Therefore there is the possibility that predators will learn to associate boxes with nests and target them specifically. This could even lead to nest boxes acting as ‘ecological traps’ – with birds using them preferentially but having very low reproductive success in them. Therefore, ‘anti-predator’ devices and boxes may be desirable.
Supporting evidence from individual studies
A replicated trial in woodland on Rhode Island, USA, in 1955-56 (Cronan 1957), found that installing predator guards on wood duck Aix sponsa nest boxes reduced the usage of nest boxes, compared to unguarded nest boxes, when birds were given a choice of boxes (55% of 40 boxes with guards used vs. 93% of 40 unguarded boxes). However, in areas where all boxes were either guarded or unguarded, there was no significant difference in usage (51% of 55 guarded nests used vs. 56% of 52 unguarded). This study is also discussed in ‘Provide artificial nesting sites’.
A before-and-after study on a marshland site in Montana, USA (Craighead & Stockstad 1961), found that Canada goose Branta canadensis nests on raised artificial nesting platforms were significantly less likely to be predated than the population average (7% of 14 failed platform nests predated vs. population average of 61% of 404 failed nests). This study is discussed in detail in ‘Provide artificial nest sites’.
A replicated, controlled study from 1958-1961 in multiple woodlots in Illinois, USA (Bellrose et al. 1964) found that wood ducks Aix sponsa had higher nesting success in nest boxes, compared to natural cavities (71% success for 574 metal nest boxes vs. 37% for 116 natural cavities). As racoon Procyon lotor predation accounted for most nest loss, the authors conclude that metal nest boxes provided some protection from predation. This study is also discussed in ‘Provide artificial nest sites’.
A replicated study on a wetland site in Missouri, USA (Brakhage 1966), found that 2% of 268 Canada goose Branta canadensis clutches in artificial nest ‘tubs’ were predated in 1962-5, compared 32% of 106 clutches laid on the ground. Artificial nests consisted of ‘No. 2 round washtubs’ placed in trees, on fence posts or specially constructed stands and partially filled with sawdust and straw to allow geese to bury unattended eggs. Tubs were placed 1-20 m off the ground (height did not affect predation rate). Some nests were still considered useable after nine years.
A trial in captivity in Illinois, USA, in the 1960s (Eaton 1966) found that raccoons Procyon lotor could enter metal wood duck Aix sponsa houses (cylindrical metal houses with a 33 cm cone on top and a 10 cm circular entrance hole) more easily if the cone on top of the house was increased beyond the standard 33 cm. However, if the cone was extended to provide a 7.6 cm overhanging roof and the distance between entrance hole and the roof was increased from 30 to 60 cm, then none of the five raccoons tested could access the nest hole. Reducing the size of the entrance hole to 8.9 x 7 cm also prevented all raccoons from entering, but the authors warn that it is not certain whether wood ducks would use such entrances.
- Cronan J.M. (1957) Effects of predator guards on wood duck box usage. The Journal of Wildlife Management, 21, 468-468
- Craighead J.J. & Stockstad D.S. (1961) Evaluating the use of aerial nesting platforms by Canada geese. The Journal of Wildlife Management, 25, 363-372
- Bellrose F.C., Johnson K.L. & Meyers T.U. (1964) Relative value of natural cavities and nesting houses for wood ducks. The Journal of Wildlife Management, 28, 661-676
- Brakhage G.K. (1966) Tub nests for Canada geese. The Journal of Wildlife Management, 30, 851-853
- Eaton R.L. (1966) Protecting metal wood duck houses from raccoons. The Journal of Wildlife Management, 30, 428-430