Individual study: Nest characteristics, fate and predation of Barrow's goldeneyes Bucephala islandica and bufflehead B. albeola nests in nest boxes and natural cavities in Cariboo Parklands, British Columbia, Canada
Evans M., Lank D., Boyd S. & Cooke F. (2002) A comparison of the characteristics and fate of Barrow's goldeneye and bufflehead nests in nest boxes and natural cavities. The Condor, 104, 610-619
This study compared nest characteristics, fate, and sources of predation of Barrow's goldeneyes Bucephala islandica and bufflehead B. albeola breeding in nest boxes and natural cavities in northwest Canada.
Study area: The study was conducted between April and September, 1997-1999, in the Cariboo Parklands (52°07'N, 122°27'W), British Columbia, Canada. The area was characterized by a mixture of naturally fragmented deciduous and coniferous forest among grasslands and prairie pothole wetlands.
Nest boxes: Barrow's goldeneye and bufflehead nest boxes have been present since 1981. In 1998 and 1999, boxes were repaired or replaced, and more boxes were added to some areas. By 1999, 234 goldeneye boxes (139 boxes: 39 x 25 x 26 cm high, 11 — 13 cm entrance size; 71 boxes: 50 — 25 — 28 cm high, 11 — 10 cm entrance; 24 boxes: 41 — 25 — 26 high, 12 — 12 entrance) and 118 bufflehead boxes (43 boxes: 28 — 15 — 15 cm high, 7 — 7 cm entrance; 54 boxes: 32 — 18 — 20 cm high and 8 — 8 cm entrance; 21 boxes: 28 —18 — 18 cm high and 8 — 8 cm entrance) were available. These boxes were located 3-6 m above ground in various species of trees. No predator exclusion devices were used.
Natural cavities: Natural cavity nests were located by following females returning to nests to incubate, and by searches conducted in forest surrounding lakes that had paired birds.
Monitoring: All active nest sites (boxes and cavities) were checked every 4-7 days from mid-April to July. Clutch size, hatching date, nesting success and source of predation were recorded.
Larger clutch size (nest boxes: 10.5; cavity nests: 7.5 eggs), lower nesting success, and different major predators (main predator of nests in boxes was black bear Ursus americanus; bears did not predate any cavity nest, but small mammals and starlings Sturnus vulgaris were important) were found for goldeneyes nesting in boxes versus those nesting in natural cavities.
There were few differences for bufflehead: average clutch sizes were similar in boxes: (8.4) and cavity nests (8.5 eggs), nesting success in boxes and cavities did not differ, and predation was low in all nests (American red squirrel Tamiasciurus hudsonicus and American pine marten Martes americana), responsible for nearly all predation).
This is attributed to the location and differences between Barrow's goldeneye nest boxes and natural cavities that affect their conspicuousness to predators and conspecific nest-parasitizing (egg-dumping) females. Goldeneye boxes were concentrated in highly visible locations such as trees at water or forest edge. Natural cavity nests, on the other hand, were often old pileated woodpecker Dryocopus pileatus cavities, which were more dispersed throughout the forest interior and concealed under the canopy. Bufflehead natural cavity nests were typically located closer to woodland edges (hence more exposed), which may account for their similarity with boxes.
For future nest box programs under similar circumstances, the authors recommend installing predator guards (e.g. bear deterrents) and placing boxes in less conspicuous locations.
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