Post-nuptial Wandering in Birds
The range of some species expands after nesting.
The term 'post-natal wandering' or "post-nuptial wandering" may be used to describe the movement of young birds away from the regions in which they were raised and after they have left the nest. Adult birds of some species also participate in post-nuptial wandering.
In some species, like Egrets and southern herons, the birds can be found well north of their nesting range. Cattle Egrets, for example, typically nest in the southern part of the U.S. Their range can expand as far north as into southern Canada after nesting.
Young gulls and terns may also venture far north of where they were born.
Post-nuptial wandering is particularly pronounced in birds that breed in large colonies but this is not always the case. Banding studies indicate that Western Kingbirds and Clay-colored Sparrows expand eastward after nesting. The birds are mostly first year but some adults also move east.
The post-nuptial wandering is different than migration. At the end of the summer, the birds that have wandered far north of their nesting range will start to move back to their typical range and may continue on a southern migration to their winter homes.
Birders in northern states look forward to these summer movements. Young Wood Storks, a bird that nests in Florida with a limited range in far southern Georgia and coastal South Carolina, have been recorded several times in Ohio. The young birds may have traveled over 1,000 miles north of where they were born.
The dispersal of birds after nesting is complex, which seems to be the way with birds. Natal dispersal is another category of bird movement, separate from post-nuptial wandering and migration. It is more closely associated with movements of shorter distances.
Natal dispersal may be influenced by the sex of the bird. In birds, female-biased dispersal is typical, with only about 15% of known species that have male-biased dispersal. One theory suggest that males are more likely to remain in their natal area because they must defend a nest or territory. This places a premium on their familiarity with the local resources. But there is more to the story.
Research by Fan Qiu at Kansas State University and Michael M. Miyamoto of the University of Florida studied the relationship of size to the dispersal of birds. Their study compiled published data for different dispersal and mass characters for the females and males of 92 bird species from 15 different orders. Their research revealed the larger species have more male-biased dispersal, that the dispersal distance is increasing more rapidly in males than in females, and that the female and male dispersal distances are both positively correlated with their sex-specific body masses.
All of this moving around is great for birders who will brave the summer heat in search of birds that show up in new and un-expected places.
From the Auk - Midsummer Wandering of certain Rocky Mountain Birds
Comparative Tests of Birds Support a Link between Sex-Biased Dispersal and Body Size
Journal of Phylogenetics & Evolutionary Biology