Winter Birds, Conclusion

Five years after my first winter bird survey, I operated a banding station, using mist nets for capturing birds, at the census/survey plot for a single season in the winter of 1991-92. Banding and census/survey work are two entirely different approaches for determining the number of species and their abundance on a particular site, and the two methods are not directly comparable. Mist netting is biased towards those species that spend more time at ground level or in the shrub layer or understory and rarely captures birds found at higher canopy levels. Netting is also biased against capturing the larger, sparsely distributed birds such as hawks, owls, and waterfowl. Finally, mist netting results in capturing only a limited sample of birds that actually occur at the site. Nevertheless, banding can provide some insights into the relative abundance and the number of species that occur on a given area. Banders sometimes conduct limited surveys in order to determine which birds may have been overlooked and unaccounted for during banding efforts.

My banding results revealed a total number of 77 birds representing 19 species. With one exception the most abundant banded birds were nearly the same as for the winter survey done five years earlier: American robin was the most abundant with 19 banded, followed by both ruby-crowned kinglet and yellow-rumped warbler, tied for second at 9 birds each. Robins alone represented nearly 25% of the total birds banded, and combined with the other two species resulted in 48% of the total number banded.

The one exception was the white-throated sparrow, which was 15th in abundance for the survey count done in 1986 but tied for second place with the kinglet and warbler with 9 banded in 1991-92. This difference was explained by Hurricane Hugo’s passage near the park in September, 1989, which knocked known dozens of trees on the site and created large canopy gaps. These light gaps quickly filled in with dense patches of switch cane as well as shrubs and thickets, all of which created favorable sparrow habitat.

Another difference between the banding and survey periods was the presence of red-headed woodpeckers in 1991-92 (three of which were banded), while none were observed in 1986. This was due to the lack of laurel oak acorns, their primary winter food, in 1986, while a good acorn crop was present in 1991.

Twelve years after conducting the first WBPS, I did another winter count at the same location in 1998-99. I found a total of 32 species and an average of 145 birds per visit (1,810 birds per square kilometer or 699 birds per square mile). Although four more species were found in 1998 than 1986, the density figures, while still impressively high, were slightly lower than from 1986. Much of this difference was accounted for by the reduced number of robins, less than half, as a result of a relatively poor crop of holly berries. The “Big Three” were again most abundant, although yellow-rumped warblers were just barely in first place, with an average of 22.3 birds per visit, closely followed by American robins, with 21.8 birds, and ruby-crowned kinglets in third place, with 18.4 birds per visit. Overall the three species accounted for 62% of the total individuals found on the plot, a number nearly identical with the 63% found twelve years earlier.

Red-headed woodpeckers were common in the winter of 1998 and actually ranked fifth in abundance with an average of 7.2 individuals per visit. And based on the Congaree Christmas Bird Count, 1998 turned out to have the highest number of red-headed woodpeckers ever recorded in the twenty-three year history of the count.

The number of white-throated sparrows had declined significantly at the site during the seven-year period since banding. They ranked 15th in abundance, the same rank as when the first survey count was done in 1986. This decline was explained by the fact that due to rapid canopy closure since Hurricane Hugo, the thickets and cane patches created by the hurricane had thinned out to the point that most were no longer suitable as sparrow habitat. This process of swift recovery from a significant natural disturbance (basically an eight-to-ten year period of recovery to pre-disturbance conditions) was also noted for breeding birds at the site.

Congaree’s large variety of breeding birds, many with colorful plumage and distinctive song, continues to garner most of our attention, but its winter birdlife is just as impressive. If you spend enough time there with binoculars in December, January, and February, you will understand why.