Double-crested Cormorant

Phalacrocorax auritus


Priorities for Future Research

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For such a familiar and well-discussed species, there are substantial gaps in available knowledge. In addition to those already mentioned, priority topics reflect different interests (the numbers follow the sequence of this account and are not ranks):

1. The genetic distinctiveness of the diverse populations and the extent of gene flow are prime targets for the modern tools of population genetics, combined with field observations. This information is an important basis for regional management.

2. Cormorant species are most distinctive in the colors of eye, face, and throat, yet the significance of these bright colors has not been studied in the field.

3. For clearer understanding of local impacts on prey populations and ecosystem dynamics, it will be important to know more about foraging behavior (including range and diving performance) and predator-prey interactions at different scales.

4. Anatomical and physiological adaptations and constraints for diving are worthy of study, and measures of field metabolic rates will contribute to improved estimates of fish consumption.

5. Study of cormorants killed during management activities, especially banded birds of known age, could yield useful information on a number of aspects of cormorant biology such as: molt and maturation and geographic segregation by age or sex (Dorr et al. in press).

6. For population modeling, and to develop life tables, numerous parameters need to be established reliably. Winter survival and distribution of nonbreeding birds are notably poorly understood. An extensive banding program coupled with intensive long-term study of marked individuals will be required. Research on using Biomarkers for aging could facilitate studies of population demographics (Fallon et al. 2006). Although difficult to study because so sensitive to disturbance, cormorants may readily habituate (Mendall 1936a) and become rewarding subjects. Modern analyses of existing banding records would be rewarding.

7. Means of estimating cumulative impacts of management and assess effects of lethal and reproductive control on cormorant populations are critical (Dorr and Somers 2012). Development of population models such as potential biological removal models (Runge et al. 2009) could provide important information for guiding management and policy, in light of limited demographic data (Dorr and Somers 2012, Guillaumet et al. 2014).

8. Coordinated rangewide censuses will enable the size of breeding populations to be tracked; at present major sections are poorly known, notably in the southern U.S., Manitoba, Florida, and Mexico.

9. Better understanding of management conflicts requires careful design of studies, including experimental manipulations to quantify impacts, as well as to develop new, preferably nonlethal methods of population control that minimize conflicts: by changing stocking procedures, by dispersing the birds, or by reducing their take of fish.

10. More research needs to be done identifying and evaluating the ecological, economic and social outcomes of management. As management moves from programs to reduce cormorant numbers to local maintenance of cormorant numbers, how will that affect management methods? Lastly, what management methods may be most effective in meeting objectives in the most ecologically sound way (Dorr and Somers 2012)?

For additional suggestions of research needs and divergent views of goals, see Erwin 1995b, Nisbet 1995, and Dorr and Somers 2012, and for opinions of midwestern wildlife managers, see Weseloh and Lewis 1997.

Recommended Citation

Dorr, B. S., J. J. Hatch, and D. V. Weseloh (2014). Double-crested Cormorant (Phalacrocorax auritus), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.