The double-crested cormorant (Phalacrocorax auritus) is a large waterbird found across much of North America. It’s a common sight around lakes, rivers, and coastlines, where it dives to catch small fish. But how heavy are these large, gangly birds? In this article, we’ll take a look at some key facts and figures on double-crested cormorant weights.
Average Weight
An adult double-crested cormorant typically weighs around 1.5-2.5 pounds (0.7-1.1 kg). This makes them a relatively lightweight bird compared to some other aquatic birds like swans and pelicans. Here are some more details on average cormorant weights:
Male vs Female
– Adult males tend to be larger and heavier than females. Males average about 2.2 pounds (1 kg), while females are around 1.7 pounds (0.8 kg).
Seasonal Variation
– Cormorant weights fluctuate somewhat seasonally. They tend to reach peak weights just before breeding season, then drop off while incubating eggs and raising chicks.
– On average, males weigh the most in spring at 2.5 pounds (1.1 kg) and the least in early winter at 2 pounds (0.9 kg).
– Females follow a similar pattern, weighing up to 1.9 pounds (0.86 kg) pre-breeding and down to 1.5 pounds (0.68 kg) in winter.
Regional Differences
– Geography also plays a role. The largest cormorants are found in Alaska, averaging about 10-15% heavier than populations further south.
– Smaller subspecies are found along the Gulf coast. The lightest on average weigh just over 1 pound (0.45 kg).
Maximum and Minimum Weights
While average weights give a good overview, individual cormorant weights can vary quite a bit. Here are some record weights that demonstrate the range:
Maximum Recorded Weight
– The heaviest double-crested cormorant on record weighed 4.1 pounds (1.9 kg). This was an outsized male from Alaska.
Minimum Recorded Weight
– At the other extreme, the lightest verified weight for the species was just 0.8 pounds (0.36 kg). This was a juvenile female.
– Even smaller weights have been reported, but not officially confirmed. The minimum is around 0.7 pounds (0.32 kg) based on typical hatchling weights.
Weight Changes Through Life Stages
Cormorant weights change dramatically as the birds grow and develop. Here’s an overview of how their weight increases from hatchlings to adults:
Hatchlings
– Newly hatched cormorants weigh only about 1.5-2 ounces (42-57 grams). They grow quickly thanks to constant feeding by both parents.
Fledglings
– By the time they’re ready to leave the nest at 4-5 weeks old, cormorant chicks (called fledglings) weigh around 1 pound (0.45 kg).
Juveniles
– They gradually gain weight through their first year, reaching an average of 1.3 pounds (0.6 kg) as juveniles.
Subadults
– In their second year, subadult double-crested cormorants average around 80% of adult weight as they near full maturity.
Adults
– By their third spring, they reach adult weights of 1.5-2.5 pounds, completing the growth cycle.
Life Stage | Average Weight |
---|---|
Hatchling | 1.5-2 oz (42-57 g) |
Fledgling | 1 lb (0.45 kg) |
Juvenile | 1.3 lbs (0.6 kg) |
Subadult | 1.2-2 lbs (0.54-0.9 kg) |
Adult | 1.5-2.5 lbs (0.7-1.1 kg) |
Why Do Cormorants Weigh So Much?
Now that we’ve covered some key weight figures, it’s interesting to consider why double-crested cormorants grow to the sizes they do. Here are a few of the main evolutionary factors:
Buoyancy
– All that body weight helps cormorants stay submerged when diving underwater to catch fish. More mass means less buoyancy to fight against.
Insulation
– Weight also comes from having dense, waterproof plumage to retain body heat. This insulation allows them to survive prolonged plunges into cold water.
Energy Reserves
– Finally, having ample fat stores provides an energy reserve for lean times. Cormorants experience large seasonal weight fluctuations in part due to burning these fat supplies in winter or breeding season.
How Cormorant Weight Compares to Other Birds
To put the double-crested cormorant’s average weight of 1.5-2.5 pounds in context, let’s compare it to a few other common waterbird species:
Heavier Birds
– Trumpeter swan: 25-30 lbs
– Mute swan: 20-25 lbs
– Great blue heron: 5-6 lbs
– Great egret: 2-3 lbs
Similar Weight Birds
– Pelagic cormorant: 2-3 lbs
– Brandt’s cormorant: 2-3 lbs
– Pied-billed grebe: 1-2 lbs
Lighter Birds
– Pied-winged swallow: 0.1-0.2 oz
– Belted kingfisher: 0.25-0.35 lbs
– Ring-necked duck: 1-1.5 lbs
Conclusion
In summary, the typical adult double-crested cormorant weighs 1.5-2.5 pounds. This makes them a mid-sized aquatic bird – lighter than swans but heavier than many ducks and grebes. Their weight helps them dive and swim effectively to catch fish. It also provides insulation and energy storage for their fish-centric lifestyle. While individual weights can vary substantially based on age, gender, and region, the species averages around 2 pounds across its North American range. Understanding how much cormorants and other waterbirds weigh provides useful insights into their ecology and adaptations.