The Great Cormorant (Phalacrocorax carbo) is a large waterbird in the cormorant family that inhabits coastlines and inland waters across much of Europe, Asia, Africa, Australia, New Zealand, and North America. Cormorants are medium to large sized birds with all-black plumage, long necks, hooked bills, and short legs set far back on their bodies. Their size and distinctive appearance makes the Great Cormorant a familiar sight in wetland habitats. But just how big are Great Cormorants? In this article, we will explore the typical size range of these aquatic birds.
Weight
The Great Cormorant is considered a large cormorant species. Males tend to be larger than females. Average weights range from:
- Males: 2.5-3.5 lbs (1200-1600 g)
- Females: 1.8-2.5 lbs (800-1200 g)
The largest Great Cormorants can reach weights of over 4 lbs (1800 g). By comparison, some other common waterbirds in their range include:
| Bird Species | Average Weight |
|---|---|
| Mallard | 2.5-3.3 lbs (1150-1500 g) |
| Canada Goose | 7-14 lbs (3175-6350 g) |
| Great Blue Heron | 4.5-8 lbs (2050-3650 g) |
So in terms of bulk, Great Cormorants are smaller than some of the larger ducks and geese they share habitats with, but larger than common small duck species like teal. They overlap in average size with some of the larger wading birds like egrets and herons. But overall, the Great Cormorant sits on the larger end of the spectrum for waterbirds, reflective of its fishing lifestyle requiring power and strength to pursue prey underwater.
Length
In addition to a heavyset build, Great Cormorants have an elongated profile thanks to their long necks and pointed bills. From head to tail, adults measure:
- Total Length: 31-39 in (80-100 cm)
- Wingspan: 55-71 in (140-180 cm)
The wingspan in particular allows Great Cormorants to generate thrust and propulsion for diving and swimming after fast-moving fish. Their average wingspans fall midway between ducks/geese and large herons/egrets:
| Bird Species | Wingspan |
|---|---|
| Mallard | 32-39 in (81-99 cm) |
| Canada Goose | 54-73 in (137-185 cm) |
| Great Egret | 52-67 in (132-170 cm) |
| Great Blue Heron | 59-70 in (150-178 cm) |
The cormorant’s adapted body allows it to swim low in the water and swiftly chase down fish, thanks to its powerful wings for propulsion and its long neck for spearing prey.
Skeletal Size
The size of a Great Cormorant isn’t just about its external bulk, but also its robust underlying skeleton. Some key skeletal measurements include:
- Skull Length: 4-6 in (10-15 cm)
- Total Vertebrae: 57-61
- Pelvic Bone Width: 2.5-3 in (6-7.5 cm)
For comparison, a much smaller Double-crested Cormorant has a skull length of around 2 in (5 cm) and only 33-39 vertebrae. The Great Cormorant’s large skull houses a muscular jaw and throat pouch for swallowing fish, while its extra vertebrae extend the neck and allow greater striking distance when spearing prey underwater. These adaptations allow it to handle sizable fish like eels, perch, trout, and small carp.
Sexual Dimorphism
As mentioned earlier, Great Cormorants display sexual dimorphism where males tend to be noticeably larger than females in size. Some key gender differences include:
Males
- Weight: 2.8-3.5 lbs (1300-1600 g)
- Wingspan: 63-71 in (160-180 cm)
- Total Length: 35-39 in (90-100 cm)
Females
- Weight: 1.8-2.5 lbs (800-1150 g)
- Wingspan: 55-63 in (140-160 cm)
- Total Length: 31-35 in (80-90 cm)
The larger body of males is likely an evolutionary adaptation to allow males to compete more effectively for nesting sites and mates. The size dimorphism between genders is maintained even among juvenile birds. This extra male bulk comes at a cost though – larger males require more food and are more susceptible to starvation when fish stocks are low.
Growth Rate
Great Cormorants grow rapidly from chicks to fledged juveniles. Some key benchmarks:
- Hatchling Weight: 2.5-3 oz (70-85 g)
- Fledging Age: 4-5 weeks
- Fledgling Weight: 1.5-2 lbs (750-1000 g)
So in just over a month, chicks are able to grow from a few ounces to matching or exceeding their mother’s weight. Their growth rate slows after fledging, but young cormorants continue getting larger until they reach adult size at 2-3 years of age. Their rapid growth is fueled by protein-rich fish delivered by both parents.
Population Size Dimorphism
In addition to individual size differences between genders, in some areas male and female Great Cormorants have skewed population ratios. A recent 5-year study in Poland found that males made up 56% of the Great Cormorant population there. This male skew likely reflects higher mortality among females. Possible reasons include:
- Greater starvation risk for smaller females in low fish stocks
- Higher predation rates on females by terrestrial predators at nesting colonies
- Higher frequency of females deserting chicks due to lack of parental care by males
More research is needed to understand why female numbers are diminished in certain Great Cormorant populations. Conservation efforts must take into account this gender imbalance when managing regions inhabited by these birds.
Conclusion
In summary, Great Cormorants are bulky, long-necked waterbirds that occupy an ecological niche preying on fish in inland and coastal waters. Their body size sets them apart from small diving ducks, but still smaller than giant waterfowl like swans and geese. While not as large as some iconic wading birds, Great Cormorants require greater body mass for diving after speedy prey. Sexual dimorphism allows males to claim prime nesting sites, but may come at a cost of reduced resilience. Further studies of gender size ratios in Great Cormorant populations can inform conservation. Their adaptable size helps Great Cormorants thrive across diverse aquatic habitats and continue to provide an iconic presence. Monitoring their changing size in response to environmental pressures can act as an indicator of ecosystem health for wetlands around the world.
