Methodology

The majority of the distribution and population determinations will be conducted through direct observation of the sites themselves.  This will entail traveling to impoundments and other likely target areas throughout the state to estimate bird numbers.  This will need to be done in both the winter and summer seasons in order to establish a realistic idea of how many, if any, of the birds have become sedentary and ceased to migrate. Also nest counts will need to be conducted in order to determine the status of the breeding population of cormorants in the state. As of the beginning of this project, it has been observed that Double-crested Cormorants are capable of and do nest in South Carolina.  It is our aim to assess the validity of this observation and to get an accurate count of the roosting population. Distributions will be mapped using GIS software.  Possible additional methods for observation include flyovers and real-time satellite viewing.  

Also, the rudimentary damage analysis will be done by developing a simple number rank scale, i.e. scoring a site on a scale of 1-5 with 5 being damage beyond reclamation and 1 being optimal site conditions. At each of the 6 study sites, at least one soil sample (or water if the roost happens to be over water) is to be collected from directly beneath the nests.  A second, control sample will be taken at a distance of 30 yards from the roost sample, to give an approximation of normal conditions. Samples will be analyzed to detect levels of increased ammonia and nitrogen from roost samples vs. control samples.  Results from the soil/water analyses will be paired with visual observations of habitat condition (vegetation/trees will be given a grade between 0 and 5 in regards to condition, with 0 being no remaining living vegetation and 5 being lush, ideal conditions) to determine a possible cause/effect relationship between cormorant guano buildup and vegetative decline.  Water samples will be compared to the soil samples as an auxiliary observation to see if there is a noticeable discrepancy between the two as far as negative effect of cormorant presence.

Dietary analysis will also be a primary component of our research, with the cooperation of USDA-APHIS Wildlife Services who will be collecting birds for stomach analysis. Cormorants will be received from USDA APHIS Wildlife Services in double bagged Ziploc bags and placed immediately on ice in order to slow further digestion and preserve the carcass. Cormorants will then be weighed and sexed, and this information will be recorded.   The abdomen will then be cut open and the stomach will be carefully removed, from the entrance of the esophagus to the beginning of the small intestine.  Next, the stomach of the bird will be opened with care taken not to further damage any stomach contents.  Any identifiable remnants of prey will be founded and used to make identifications.  If a large enough portion of a fish is present for true measurement, length will be taken and recorded.  However, if a significant number of fish do not meet this criteria, this data will not be used.  Next, the stomach will be completely emptied to ensure that all identifiable prey items have been removed.  Any prey items found will be grouped into one of three primary placements “Game fish” (i.e. bass, sunfish, trout, catfish, etc), “Forage fish” (shads, cyprinids, etc) and “Other” (macro-invertebrates and other unexpected finds), When all this is completed, the birds will be placed back in the Ziploc bags and back into a freezer to be incinerated with all the other carcasses.

Dietary data and energetics models will give us a clearer idea of the impacts (or lack thereof) that Double-crested Cormorants are having on commercial and/or recreational fisheries.  Finally, access to the data from this project will be provided by this website.  This site will give cooperators and other stakeholders the ability to access the project's progress and results. The information collected from this study will be used to make management recommendations to the South Carolina Department of Natural Resources for the Double-crested Cormorant.