A COMPARISON OF THE BREEDING ECOLOGY OF A SECONDARY CAVITY NESTING BIRD, THE TREE SWALLOW (TACHYCINETA-BICOLOR), IN NEST BOXES AND NATURAL CAVITIES

Nest site dispersion and cavity height were similar for birds in both nesting environments. Greater cavity entrance area at natural cavities resulted in increased interspecific competition in natural populations, involving larger competitors, more species, and a greater abundance of each species. Clutch size was smaller in natural cavities compared with nest boxes, likely because floor area was smaller in natural cavities. Fledging success did not differ between populations. Disproportionately more after-2nd-year females bred in nest boxes, and more 2nd-year females bred in natural cavities. Tree swallows settled at nest boxes before natural cavities, perhaps as a result of the greater potential for reproductive success and reduced interspecific competition in the nest boxes. For some aspects of the ecology of secondary cavity nesters, nest boxes do not provide an accurate representation of natural populations. -from Authors