Action: Provide artificial nesting sites for woodpeckers
- Four studies from the USA found local increases in red-cockaded woodpecker Picoides borealis populations or the successful colonisation of new areas following the installation of ‘cavity inserts’ (described above). One study also found that the productivity of birds using the inserts was significantly higher than the regional average.
- Two studies from the USA found that red-cockaded woodpeckers Picoides borealis used cavity inserts, in one case more frequently than making their own holes or using natural cavities. One study from the USA found that woodpeckers roosted, but did not nest, frequently in nest boxes.
- Five studies from the USA found that some woodpeckers excavated holes in artificial snags but only ever roosted in excavated holes or in nest boxes provided.
- A small study in the USA found that modifying artificial nests to allow easy access did not alter the behaviour of birds using them.
Woodpeckers typically nest in hollows in trees. These are normally hollowed out from soft wood. Therefore, if this substrate is lacking in a site, providing it may be beneficial. Providing dead wood and ‘snags’ is described in ‘Natural system modifications’, whilst providing artificial snags, typically made of polystyrene cylinders is described below.
Alternatively, ‘cavity inserts’ can be provided. These consist of a nest box inserted into a tree. Full details of their installation can be found in Allen (1991), but basically consist of cutting a 10 x 25 x 6 cm block out of a live tree and gluing a nest box into place to give the impression of a tree with a hole and a nesting cavity. These inserts are used most frequently to provide nesting habitats for red-cockaded woodpeckers Picoides borealis.
Allen DH (1991) An insert technique for constructing artificial red-cockaded woodpecker cavities. Southeastern Forest Experiment Station General Technical Report SE-73, United States Forest Service.
Supporting evidence from individual studies
A controlled study 1977-9 in riverine forests in Louisiana, USA (McComb & Noble 1981), found that neither northern flickers Colaptes auratus nor red-bellied woodpeckers Melanerpes carolinus (formerly Centurus carolinus) nested with any frequency in nest boxes provided, with only a single woodpecker nest found in 5,374 inspections of 235 boxes. Both species, as well as red-headed woodpeckers M. erythrocephalus and hairy woodpeckers Picoides villosus (formerly Dendrocopus villosus) used nest boxes for roosting. Boxes were of three sizes between 30 x 15 x 15 cm with a 5.0 x 7.0 cm entrance hole and 60 x 30 x 30 cm with a 13 cm diameter entrance. All boxes had 5-10 cm of pine shavings in the bottom. This study also examined nest box use by other birds (wildfowl, owls and songbirds).
A replicated trial in 1980 in woodlots in Ohio, USA (Grubb 1982), found that downy woodpeckers Picoides pubescens were more likely to excavate cavities in artificial snags of intermediate height (242 cm tall, ten of 16 snags used), compared to tall (363 cm tall, five of 16 used) or small (121 cm tall, one of 16 used) snags. There was some evidence that males preferentially excavated holes in intermediate or tall snags, whilst females preferred small or intermediate ones. Snags were polystyrene cylinders, 22.5 cm in diameter, painted brown and mounted on metal poles.
A replicated trial in 1979-80 in a deciduous forest in Ohio, USA (Peterson & Grubb 1983), found that downy woodpeckers Picoides pubescens excavated 51 roosting cavities in 42 artificial snags. Raccoons Procyon lotor destroyed 18 cavities, with woodpeckers excavating new holes near nine of these. Two species of songbird used cavities excavated by woodpeckers (see ‘Provide artificial nesting sites for songbirds’ for details). Snags were polystyrene cylinders 242 cm high, 22 cm diameter and were erected 10 cm above ground on metal poles. A total of 50 cylinders were erected. Laboratory tests showed that polystyrene did not have a negative impact on woodpecker health.
A replicated trial in 1982-3 in an area of forest clear-cut 12 years previously in Ohio, USA (Petit et al. 1985), found that a total of 34 cavities were excavated in 99 artificial snags erected in autumn 1982. Thirty one of these were probably excavated by downy woodpeckers Picoides pubescens, with the remaining three probably being excavated by hairy woodpeckers P. villosus, red-bellied woodpeckers Melanerpes carolinus or northern flickers Colaptes auratus. Only downy woodpeckers were found roosting in cavities. Excavation rates were highest within 35 m of the edge of the clear-cut. Snags were polystyrene cuboids, 21 x 21 x 237 cm, erected vertically on a fibreglass stake on a 16 m grid.
A replicated, controlled, paired site study from April-July in 1988-9 in 20 experimental and 20 control sites of nesting cavities in a forest reserve in North Carolina, USA (Copeyon et al. 1991) found that red-cockaded woodpeckers Picoides borealis used artificial nesting cavities significantly more than creating their own or using abandoned cavities. Woodpeckers were significantly more likely to occupy vacant experimental sites (nine occupied) than vacant control sites (zero occupied). Similarly, abandoned experimental sites were occupied more (nine occupied) than control sites (none occupied). Abandoned sites lacking artificial cavities were never occupied. The 18 experimental sites occupied corresponded to a net addition of 12 social units to the population. Out of six breeding pairs, four nested successfully, raising seven young, while 2 failed. Vacant (previously unoccupied) experimental sites (provisioned with two cavities) were paired with ten control (no cavities provided) sites and were matched in habitat characteristics. Similarly, ten abandoned experimental sites were matched with abandoned control sites.
A small trial at two open pine woodland sites in Texas, USA (Rudolph et al. 1992), found that all four translocated red-cockaded woodpeckers Picoides borealis that remained at two release sites (see ‘Translocate individuals’ for details) used artificial nesting cavities provided at the release sites.
A series of before-and-after trials in four open pine forests in Texas, USA (Conner et al. 1995), investigated the impact of multiple interventions, including the provision of 736 artificial cavities (mostly ‘inserts’), on red-cockaded woodpecker Picoides borealis populations. Following declines throughout much of the 1980s, numbers of active clusters stabilised, with increases apparent at all four sites in the early 1990s and a total 39 new clusters established, 22 of which were in areas with artificial nesting sites. Restrictor plates were also installed around red-cockaded woodpecker nesting holes to prevent enlargement of cavities by pileated woodpeckers Dryocopus pileatus. This study is discussed in more detail in ‘Translocate individuals’ and ‘Use prescribed burning’.
A replicated trial in 1986-91 in five forest types in Texas, USA (Conner & Saenz 1996), found that downy woodpeckers Picoides pubescens excavated cavities in all ten artificial snags installed in upland hardwood forest, and 13 of 17 snags provided in pine-hardwood habitats. However, they did not use any of ten artificial snags installed in pine-only forest, whilst ten in bottomland hardwood forest were not used in 1989, after which they were washed away in floods. Downy woodpeckers did not use snags for nesting and none of the other six woodpeckers in the area used the snags at all. Snags were brown-painted polystyrene cylinders, 26 cm in diameter, 242 cm tall and mounted on iron posts.
A small study in open pine forests in South Carolina, USA (Edwards et al. 1997), found that modifying seven red-cockaded woodpecker Picoides borealis inserts did not alter the behaviour of the male woodpeckers using the inserts. They were modified by drilling a 7.7 cm hole in the front, approximately 12 cm below the entrance and fitting a plug in it. The purpose was to allow easy inspection of the inserts.
A single site study from 1985-1996 in a pine forest in South Carolina, USA (Franzreb 1997) found that the number of breeding pairs of red-cockaded woodpeckers Picoides borealis increased from one to 19, producing 43 fledglings, and the overall population size grew from four to 99 individuals following the provision of artificial nest cavities amongst other interventions. The mean fledging success for 1985-96 was 2.3 fledglings/nest, which was significantly higher than the regional average (1.7 fledglings/nest). A total of 305 artificial nest cavities, fitted with metal plates to prevent enlargement by other species (see ‘Protect nest sties from competitors’), were installed over the study period. In addition, the forest midstorey was thinned and prescribed burning used (see ‘Threat: Natural system modifications – Forest modifications’), and birds. Nests were monitored monthly throughout the year except over the breeding season (April-July) when they were monitored weekly.
A before-and-after trial in a longleaf pine Pinus palustris forest in Louisiana, USA (Carrie et al. 1998), found that the number of groups of red-cockaded woodpeckers Picoides borealis with breeding pairs increased from 22 (68% of all groups) to 28 (93%) between 1993 and 1995, following the installation of 44 artificial nesting cavities in 1993-5 (55 cavities were already available in 1993). In 1993-5, the number of groups in the area decreased from 33 to 30, but average group size increased, as did the number of groups with helpers and the number of cavities occupied. Most breeding males (77% of 30 birds) continued to use natural cavities, but 71% of 28 breeding females and 65% of 23 helper birds used artificial cavities. Cavities consisted of wooden boxes 10 x 15 x 25 cm with 4.5 cm diameter, 6.5 cm long entrance tunnel and a cylindrical 20 cm x 7.5 cm diameter cavity inside. Cavities were inserted into holes carved out of live pine trees, at either 4 or 7.5 m above ground.
- McComb W.C. & Noble R.E. (1981) Nest-box and natural-cavity use in three mid-south forest habitats. The Journal of Wildlife Management, 45, 93-101
- Grubb T.C. Jr. (1982) Downy woodpecker sexes select different cavity sites: an experiment using artificial snags. Wilson Bulletin, 94, 577-579
- Peterson A.W. & Grubb T.C. (1983) Artificial trees as a cavity substrate for woodpeckers. The Journal of Wildlife Management, 47, 790-798
- Petit K.E., Grubb T.C. Jr. & Reichhardt L.J. (1985) Habitat and snag selection by woodpeckers in a clear-cut: an analysis using artificial snags. Wilson Bulletin, 97, 525-533
- Copeyon C.K., Walters J.R. & III J.H.C. (1991) Induction of red-cockaded woodpecker group formation by artificial cavity construction. The Journal of Wildlife Management, 55, 549-556
- Rudolph D.C., Conner R.N., Carrie D.K. & Schaefer R.R. (1992) Experimental reintroduction of red-cockaded woodpeckers. The Auk, 109, 914-916
- Conner R.N., Rudolph D.C. & Bonner L.H. (1995) Red-cockaded woodpecker population trends and management on Texas national forests. Journal of Field Ornithology, 66, 140-151
- Conner R.N. & Saenz D. (1996) Woodpecker excavation and use of cavities in polystyrene snags. Wilson Bulletin, 108, 449-456
- Edwards J.W., Stevens E.E. & Dachelet C.A. (1997) Insert modifications improve access to artificial red-cockaded woodpecker nest cavities. Journal of Field Ornithology, 68, 228-234
- Franzreb K.E. (1997) Success of intensive management of a critically imperiled population of red-cockaded woodpeckers in South Carolina. Journal of Field Ornithology, 68, 458-470
- Carrie N.R., Moore K.R., Stephens S.A. & Keith E.L. (1998) Influence of cavity availability on red-cockaded woodpecker group size. Wilson Bulletin, 110, 93-99