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Sunlight on feathers inhibits feather-degrading bacteria.

Article Excerpt
Sun-bathing is a conspicuous maintenance behavior of birds with several possible explanations. Simmons (1986) suggested that sunning is important in thermoregulation and synthesis of vitamin D from uropygial oil. Blem and Blem (1993) suggested that sunning is important for drying wet plumage, and Moyer and Wagenbach (1995) found that sunning dislodges ectoparasites such as lice, mites, and fleas. Black Noddies (Anous minutus) endured heat stress as temperatures on the wing feathers during sunning reached 63.4 [+ or -] 0.9[degrees]C, which caused feather lice to abandon their refuges between the barbs thereby exposing themselves to removal by preening (Moyer and Wagenbach 1995). We suggest that exposure of feathers to sunlight during sunning may inactivate or inhibit feather-degrading bacilli thereby limiting the damage such bacteria cause to the plumage of birds (Burtt and Ichida 1999, Muza et al. 2000).

Bacillus licheniformis is a common soil-dwelling bacterium that degrades feathers (Williams et al. 1990). It occurs in the plumage of 23 (Burtt and Ichida 1999) to 59% (Whitaker et al. 2005; Burtt et al., unpubl. data) of wild birds. B. licheniformis is thermophilic and able to sporulate under adverse conditions such as extreme heat and desiccation (Setlow 1995). Thus, it can resist the intense heat of sunning, but its ability to tolerate exposure to solar ultra-violet (UV) and visible radiation during sunning is unknown. Previous studies of UV resistance in Bacillus spp. (Nicholson 1995, Setlow 1995) have been based on a ~254 nm laboratory source of ultra-violet radiation, although the earth's surface is shielded from UV-C (200-280 nm) by the ozone layer (Koller 1965). Furthermore, Setlow (1995) and later Slieman and Nicholson (2000) focused almost exclusively on Bacillus subtilis, which degrades feathers poorly or not at all. We studied the effect of sunlight (280-750 nm) on growth of feather-degrading Bacillus licheniformis by assessing the viability of bacilli sprayed on domestic goose (Anser anser) feathers and exposed to sunlight.

METHODS

The experiment was conducted in summer 2003 and repeated in summer 2004 with an additional control for evaluating structural damage to feathers from UV alone. Differences between the experiment and its replication are detailed as necessary. We used white contour feathers of nearly uniform length (~4 cm each) randomly selected from a collection of similar goose feathers to test the effect of sunlight on B. licheniformis. We sterilized three (2003) or four (2004) Fisherbrand Redi-tip pipette boxes (13 x 10 cm) with 70% ethanol and mounted eight similar feathers with no visible damage onto the sides of each box (Fig. 1).

[FIGURE 1 OMITTED]

The feathers remained suspended without overlap or contact from other feathers or the sides of the boxes throughout the experiment. The boxes with mounted leathers were sterilized at 121[degrees]C and 1.3 kPa for 15 min in sealed envelopes to prevent subsequent contamination. We inoculated a Trypticase Soy Agar (TSA; Acumedia, Troy, Ml, USA) plate with B. licheniformis (strain OWUI38B, ATCC# 55768) using a sterile inoculating loop in a laminar flow hood. After 48 hrs of incubation at 37[degrees]C, we removed several bacterial colonies from the plate and suspended the bacteria in sterile, physiological saline (0.85% NaCl). We adjusted the turbidity of the bacterial suspension by visually matching it to a 1.0 MacFarland standard (~3 x [10.sup.6] cells [ml.sup.-1] ; MacFarland 1907). We transferred...