Action: Clean nest boxes to increase occupancy or reproductive success
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- Five studies from Spain and North America found that various songbirds preferentially nested in cleaned nest boxes, compared to used ones. One study from the USA found that eastern bluebirds showed this preference, but most did not switch from a soiled to a cleaned nest box. One study from the USA found that birds showed an avoidance of heavily-soiled boxes and one from Canada found that tree swallows Tachycineta bicolor preferentially selected nests which were sterilised by microwaving.
- Two studies from the USA found that eastern bluebirds Sialia sialis and house wrens Troglodytes aedon preferentially nested in uncleaned nest boxes, and one study found that prothonotary warblers Protonotaria citrea showed no preference for cleaned or uncleaned boxes.
- None of the five studies that investigated it found any difference in success or parasitism levels between cleaned and uncleaned nest boxes.
Old nest boxes may contain parasites and so reduce breeding success in them, or they may provide a suitable base for building new nests. Cleaning them out may, therefore, have a positive or a negative impact on nest site choice and reproductive success.
Supporting evidence from individual studies
A replicated controlled study in 1993 in wooded pasture in Kentucky, USA (Davis et al. 1994), found that eastern bluebirds Sialia sialis preferentially occupied nest boxes containing old nests when given the choice (93% of 41 boxes occupied contained old nests). One hundred boxes were presented in pairs, one empty and one containing an old nest at 50 sites previously used by bluebirds. Boxes had a 10 x 10 cm base and a 2.9 x 10 cm entrance and were erected 1.5 m above ground.
A replicated, controlled study in 1993-4 in two areas of montane oak Quercus pyrenaica forest in the Community of Madrid, Spain (Merino & Potti 1995), found that pied flycatchers Ficedula hypoleuca preferentially nested in nest boxes which had no old nesting material in them, although this preference was only significant in 1994 (approximately 75% of clean nest boxes occupied vs. 18-50% of boxes with old material inside). The authors note that 55% of the boxes with old nests in were completely cleaned in 1993, suggesting an aversion to old nesting material. In 1993, nest material was removed from all boxes before being replaced in 20 boxes (leaving 39 clean); in 1994, nest material was removed from 17 boxes, with 13 left with old material inside.
A replicated, controlled study in 1993-4 in woodland patches in Wyoming, USA (Johnson 1996), found that house wrens Troglodytes aedon showed no preference for cleaned nest boxes over controls with old nests in (46% of 59 pairs used cleaned boxes, 54% used controls). However, only 27% of heavily soiled boxes (with thick layers of dried faeces in) were used if they contained old nests, compared to 68% of used boxes which were only lightly soiled. There were no differences in reproductive output or blow fly infestations between nest box types. Forty (in 1993) or 50 (1994) pairs of boxes, one cleaned and one with an old nest in, were erected less than two metres apart across the study area.
A replicated, controlled study in 1993 in a floodplain and forest site in Illinois, USA (Pacejka & Thompson 1996), found that house wrens Troglodytes aedon nested in a lower proportion of cleaned nest boxes, compared to control boxes containing old nests (49% of 111 cleaned nest boxes used vs. 62% of 107 uncleaned boxes). There were no differences in reproductive output (5.5 nestlings/clutch surviving until 12 days old in cleaned nests vs. 5.2 in uncleaned nests, total of 24 nests examined) or mite infestation rates between box types. All boxes had been successfully used in 1992, with old nesting material removed from approximately half of them.
A replicated, controlled trial in marshland in 1991 in British Columbia, Canada (Rendell & Verbeek 1996), found that tree swallows Tachycineta bicolor preferentially nested in empty and clean boxes, but also preferred those where the old material had been microwaved to those with old, untouched nesting material (40 of 54 cleaned boxes used vs. 25 of 50 microwaved boxes and 13 of 54 untouched boxes). Pairs of boxes from different treatments were erected 3 m apart in tree swallow territories and which box was used was recorded.
A replicated, controlled study in marshland in 1991-2 in British Columbia, Canada (Rendell & Verbeek 1996), found that tree swallow Tachycineta bicolor reproductive success was not affected by removing old nesting material from nest boxes, removing nesting material and adding a raised ‘floor’ to simulate old nesting material or microwaving old nesting material. In 1992, cleaned birds using cleaned boxes laid and hatched eggs significantly earlier than those using other nest types (first eggs laid on 15th May and hatched on the 2nd June for 37 cleaned boxes vs. 18-20th May and 4-6th June for 68 others). Bird fleas Certaophyllys idius were more numerous in boxes with old nesting material. Use of boxes is discussed in ‘Provide artificial nesting sites’.
A replicated, controlled study in mixed farmland in South Carolina, USA (Gowaty & Plissner 1997), found that, in 1988, eastern bluebirds Sialia sialis were more likely to reuse nest boxes cleaned after the season’s first breeding attempt, compared to control (uncleaned) boxes (72% of 12 cleaned boxes reused vs. 57% of 12 controls). However, there were no differences in nesting success or overall number of nesting attempts between cleaned and control boxes (44% nesting success, 1.7 fledglings/second clutch and 24 nesting attempts for cleaned boxes vs. 50% success, 2.1 fledglings/second clutch and 26 attempts in control boxes), or in the likelihood of nest boxes being reused in 1989 (92% of 12 cleaned boxes used vs. 75% of controls). Alternative nest boxes were erected 200 m from previously used boxes, with 50% of new and 50% of old boxes being cleaned.
A replicated, controlled study in a tidal swamp in Virginia, USA (Blem et al. 1999), found that prothonotary warblers Protonotaria citrea showed no preference for cleaned nest boxes compared to control boxes with old nests in (32-38% of 164 cleaned boxes vs. 26-41% of 136 controls). The presence of an old nest did not affect laying date, clutch size, nestling mortality or brood parasitism by brown-headed cowbirds Molothrus ater (first eggs laid on 4th May, average of 5.1 eggs/clutch and 4% parasitism for both cleaned and control boxes; 14% egg and nestling loss for cleaned boxes vs. 10% for controls). Overall, warblers built 207 nests in 300 nest boxes provided.
A replicated study in North Carolina, USA (Stanback & Dervan 2001), found that eastern bluebirds Sialis sialis preferentially selected cleaned nest boxes over uncleaned boxes, with 71% of 45 pairs switching from a previously-used box to an unused one. However, if successful nest boxes were cleaned then 75% of 32 pairs remained in the same box, rather than moving to an identical, cleaned box.
A replicated paired study in 1996-7 in North Carolina, USA (Stanback & Rockwell 2003), found that eastern bluebirds Sialia sialis preferentially used clean woodcrete nest boxes over woodcrete boxes that had already been used once in the year, with 71% of 45 pairs switching boxes. However, 73% of 26 pairs did not switch from a soiled woodcrete box to a clean wooden box. The preference for different box types is discussed in detail in ‘Provide artificial nest sites’.
- Davis W.H., Kalisz P.J. & Wells R.J. (1994) Eastern bluebirds prefer boxes containing old nests. Journal of Field Ornithology, 65, 250-253
- Merino S. & Potti J. (1995) Pied flycatchers prefer to nest in clean nest boxes in an area with detrimental nest ectoparasites. The Condor, 97, 828-831
- Johnson L.S. (1996) Removal of old nest material from the nesting sites of house wrens: effects on nest site attractiveness and ectoparasite loads. Journal of Field Ornithology, 67, 212-221
- Pacejka A.J. & Thompson C.F. (1996) Does removal of old nests from nestboxes by researchers affect mite populations in subsequent nests of house wrens? Journal of Field Ornithology, 67, 558-564
- Rendell W. & Verbeek N. (1996) Old nest material in nest boxes of tree swallows: effects on nest-site choice and nest building. The Auk, 113, 319-328
- Rendell W. & Verbeek N. (1996) Old nest material in nestboxes of tree swallows: effects on reproductive success. The Condor, 98, 142-152
- Gowaty P.A. & Plissner J.H. (1997) Breeding dispersal of eastern bluebirds depends on nesting success but not on removal of old nests: an experimental study. Journal of Field Ornithology, 68, 323-330
- Blem C.R., Blem L.B. & Berlinghoff L.S. (1999) Old nests in prothonotary warbler nest boxes: effects on reproductive performance. Journal of Field Ornithology, 70, 95-100
- Stanback M. & Dervan A. (2001) Within-season nest-site fidelity in eastern bluebirds: disentangling effects of nest success and parasite avoidance. The Auk, 118, 743-745
- Stanback M. & Rockwell E. (2003) Nest-site fidelity in eastern bluebirds (Sialia sialis) depends on the quality of alternate cavities. The Auk, 120, 1029-1032