Timing of breeding and the seasonal importance of passerine prey to northern harriers (Circus cyaneus)

摘要: Despite a numerical and functional dependence on microtine mammals, breeding northern harriers (Circus cyaneus) in New Brunswick preyed upon large numbers of young passerine birds following the hatch their own nestlings. An independent index juvenile availability showed that harrier pairs switched to passerines as soon they became available, not simply because had hatched. Many nests which hatched during period high fledging success, but mean was significantly lower than early nests. A seasonal decline success highly significant, so if an adaptive temporal strategy exists, it may be breed possible and, not, coincide with flush passerines. We conclude coincidence prey nesting seasons is likely fortuitous strategic.