Cormorant (Phalacrocorax carbo)

Overview & Recent Trends

Historically, cormorants were almost exclusively coastal in the UK. But since the 1950s, they have increasingly colonized inland waters.

The UK population now includes two races (or forms). The continental race (often sinensis) is thought to play a major role in inland colonization.

They use roosting sites repeatedly, sometimes with strong site fidelity (i.e., returning to the same places).

Key Statistics

Status: Common in the UK.

Weight: ~ 2.3 kg (typical)

Eggs per clutch: 3–4 (occasionally 3–6)

Incubation period: 28–31 days (shared by both male and female)

Fledging time: ~ 48–52 days

Lifespan / Survival: • Typical life expectancy after reaching breeding age: ~ 11 years • Maximum recorded from ringing data: ~ 21.5 years • Annual adult survival rate: ~ 0.88 • First-year (juvenile) survival: ~ 0.58

Distribution & Habitat

Breeding range (UK): 8,900 breeding pairs in earlier surveys.

Wintering Population (UK): ~ 65,000 individuals (2012–17 data)

Range Expansion: • From 1997 to 2022, wintering range expanded by ~ 51%. • Breeding range has also expanded considerably inland: ~ 41.3% increase (1968–72 vs 2008–11)

Habitat: In the breeding season, cormorants are most often found in estuaries but also use inland water bodies.

Seasonality: They are present in the UK year-round, with patterns of occurrence changing over weeks/seasons.

Movement & Migration

Ringing and recovery data show that UK birds move between sites, with some foreign recoveries indicating connections across Europe.

European movement maps suggest some migratory behavior and interconnection between populations, though not all individuals migrate far.

Biology & Reproduction

Usually one brood per year.

Egg dimensions typically ~ 66 × 40 mm, weighing about 58 g (shell ~11% of weight).

Nesting: both parents incubate and care for young.

The species is altricial (i.e. young hatch relatively helpless) and naked (no down) at hatching.

Threats, Conflicts & Conservation Notes

The inland expansion has led to conflict with fisheries and anglers, who often regard cormorants as competitors for fish.

Control measures like culling or shooting (under licence) have been tried, but BTO notes they have not shown detectable effects on population trends in the UK.

Population models suggest that focusing on managing damage (rather than large-scale culling) may be more cost-effective.

Some coastal colonies have declined even as inland ones rise; drivers of change remain unclear.

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