Introduction

Range and Habitat of Double-crested Cormorants
The cormorants involved in this study are typically divided into five separate breeding populations: Alaska, Pacific Coast, Interior, Atlantic, and Southern.  Some of these groups however, have begun to overlap due to recent population explosions.  Another recent trend is that the birds located in the southeastern United States have become primarily sedentary (Johnsgard 1993).  As with most birds, cormorants choose their habitat based on two primary factors; a suitable nesting ground and nearby feeding grounds (Wires et al. 2001).  They tend to choose from a variety of coastal/aquatic areas including ponds, lakes, slow-moving rivers, lagoons, estuaries, open coastlines, and small islands when they can be found.  Nests are either arboreal or on the ground, and are often found on man-made structures.  They nest directly above or near water (Hanisch 2003).  They typically stay in the colony for the majority of the time, leaving to fish, or in some cases, to establish auxiliary night roosts.

Diet and Foraging Strategies of Double-crested Cormorants
One of the primary areas of concern, when it comes to managing this bird, is the food it does or does not eat. They are extremely opportunistic eaters that have been proven to take easy to catch fish over quality fish, and abundance is a much more important factor than size in food selection (Glahn et al. 1998).   Though they seem to prefer fish greater than 7.3 cm in length (Hanisch 2003), they will feed and consume almost any food item that is available.  A diurnal feeder, Double-crested Cormorants dive from the surface and pursues fish underwater.  Group hunting has been observed among cormorants in other parts of the United States, though deep water hunting is typically done alone.  Cormorants around the country hunt at different depths of the water column, but typically hunt within 5 km of shore and in water 8 m or shallower in depth (Hatch and Weseloh 1999). 

Management Concerns
There are several reasons that the Double-crested Cormorant presents a management concern to biologists.  They tend to be very destructive to their chosen colony sites, harass more desirable bird colonies, and may affect both sport fisheries and aquaculture ponds.  Cormorant guano has been shown to change the chemistry of the soil where their colonies are located by increasing concentrations of phosphorous, nitrogen, and potassium.  Increases in soil ammonium levels have also been shown and this can greatly contribute to a forest’s decline, in some places completely removing forest cover. (Hebert et al. 2005).  This same habitat degradation causes issues for other colonial birds that nest in their vicinity, particularly herons and egrets, because the cormorants can both out-compete these birds for the territory and then destroy roosting and  nesting habitat (Hanisch 2003).
As stated previously, there is significant concern that Double-crested cormorants impact commercial and recreational fisheries.  Though they are typically opportunistic feeders, if commercially important or federally-listed fish are the easiest or only prey available, the cormorants can in fact have a significant impact on their populations.  One little known danger that cormorants pose to humans is through their excrement they can transmit coliform bacteria, streptococcus, Salmonella, toxic chemicals, and are shown to in some areas affect local water quality (Hanisch 2003).  All of these are very valid concerns as to why a closer look should be taken at the Double-crested Cormorants in South Carolina.