The Northern gannet (Morus bassanus) is a large seabird and the largest member of the gannet family Sulidae. Gannets are known for their spectacular plunge-diving fishing behavior and large nesting colonies. Northern gannets breed in the North Atlantic Ocean, with the largest colonies found in Canada, Iceland, Ireland, Norway, Scotland, and Wales. Their nesting habits and preferred nesting sites have been studied extensively by ornithologists.
Nesting on cliffs
Northern gannets almost exclusively nest on cliffs and rocky islands, usually on ledges or grassy areas. The cliffs provide protection from predators and unfavorable weather. Gannets do not build nests out of materials like twigs or grass. Instead, their nest consists of the bare ground, rocks, or turf. Sometimes they will arrange rocks, seaweed, and other debris to form a low rim around the nest site.
Gannet colonies are tightly packed, with each nest spaced just 1-2 feet apart. This crowded nesting behavior offers additional protection and facilitates social interactions. It also allows the birds to take off and land easily while minimizing the amount of flapping needed. The nest density ranges from 0.3-3 nests per square meter.
Ideal nesting cliffs
Ideally, Northern gannets seek towering cliffs that are 100-300 feet above sea level. The cliffs should have broad ledges, grassy areas, or terraces suitable for nesting. Sheer cliff faces with narrow rocky ledges are not preferred. Gannets appear to favor cliffs made up of softer sedimentary rocks rather than hard igneous or metamorphic rock. The softer stone wears away more easily, leaving ledges and alcoves for nesting.
Northern gannets exhibit high nest site fidelity. They prefer to return to the exact spot where they nested in previous seasons. This behavior leads to the long-term occupancy of large gannetries. The breeding colonies are highly philopatric, meaning they use the same nesting grounds across generations rather than establishing new colonies.
Prime locations
Some of the prime Northern gannet nesting habitats in the North Atlantic include:
Northern Canada and Quebec
There are massive Northern gannet colonies along the sea cliffs of northern Quebec and coastal Labrador. They nest on islands off the eastern shore of Quebec’s Ungava Peninsula and on the steep cliffs along the Lower North Shore region of Quebec. Key nesting sites include Cape Wolstenholme, Bird Rocks, Great Bird Rock, and Bonaventure Island.
Western and Northern Scotland
Northern gannets breed on the Outer Hebrides, Shetland Islands, and other island groups off Scotland’s northwest coast. Major colonies are found on the rock stacks of St. Kilda, Sula Sgeir, and Bass Rock. The towering sea cliffs on the island of Foula also support a large gannet colony.
Wales
Grassholm Island, off the coast of Southwestern Wales, has one of the largest Northern gannet colonies in the world. Around 40,000 pairs nest on the island’s rocky cliffs and slopes.
Ireland
Ireland’s rocky coastal islands provide ideal habitat for breeding colonies. Some significant Irish gannetries include Little Skellig, Bull Rock, and the Saltee Islands off the southeast coast. The sheer granite cliffs of County Donegal’s sea stacks also support nesting.
Iceland
Northern gannets nest on sea cliffs along Iceland’s southern and western coasts. The main colonies are found at Krýsuvík, Heimaey, Látrabjarg, and Papey.
Norway
Norway’s network of offshore rocky islands contains northern gannet colonies. Bunes, Syltefjord, and Runde are some notable nesting sites. Runde Island hosts around 20,000 breeding pairs.
Gulf of Saint Lawrence, Canada
The Northern Gannets nest on isolated rocky islands and steep cliffs along the coasts of Newfoundland, Labrador, and Quebec. Huge breeding colonies exist at Cape St. Mary’s, Funk Island, and Baccalieu Island.
Germany and Denmark
Smaller Northern Gannet colonies are found along the coasts and islands near Denmark and Germany. Sylt, Helgoland, and Rømø are major breeding sites in this region.
Nesting materials
As mentioned above, Northern Gannets do not construct elaborate nests. But they will arrange some materials around the nest site:
Seaweed
Northern Gannets often collect seaweed from nearby beaches and arrange it around the periphery of the nest site. The seaweed helps mark territorial boundaries and provides a low wall around the nest.
Driftwood
Small pieces of driftwood, shells, and other debris may be incorporated into the nest site decoration. These items likely serve more as territorial markers than structural nest building materials.
Feathers and grass
Northern Gannets may line the nest with any available grass, leaves, moss or feathers. But quantites are minimal since no substantial nest structure is built.
Guano
The accumulated guano (bird droppings) of gannets using the site over many seasons hardens to form a crusty base for the nest. Northern Gannets exhibit high nest fidelity so guano accumulates in a long-used nesting spot.
Characteristics of nesting colonies
Northern gannet nesting colonies share the following characteristics:
Huge populations
Northern gannet colonies can be massive, sometimes containing over 100,000 nesting pairs. Even smaller colonies number in the tens of thousands of birds. The large colony size helps deter predators.
Extremely densely packed
Nests within a gannet colony are packed together as closely as the terrain permits, often with just inches between neighboring nests. The density provides protection and facilitates social interaction between the birds.
Synchronized breeding
Northern gannets in a colony engage in highly synchronized breeding. Most pairs lay their single egg within a few days of each other. The result is that eggs hatch and chicks fledge together in the colony. Synchrony may improve communal defense against predators.
Long-term occupancy
Once established, Northern gannet colonies are typically occupied year after year for centuries or longer. The birds exhibit extreme nest fidelity to their ancestral breeding grounds.
Low species diversity
At Northern gannet nesting colonies, gannets are typically the overwhelmingly dominant species present. Occasionally other seabirds like cormorants or gulls may nest on the periphery but the vast majority of birds are gannets.
Olfactory cues
Northern gannets likely use smell to establish and relocate nest sites. Nest materials and guano accumulate complex odors over time that the birds may recognize. Olfactory cues guide their nest fidelity.
Adaptations for nesting
Northern gannets possess adaptations that help them thrive at crowded cliffside nesting colonies:
Cliffside roosting
Sharp claws allow Northern gannets to grip rocky ledges securely. They can stand firmly upright on narrow cliffs that would be impossible for most birds.
Ground takeoff and landing
Despite their large size, gannets can take flight from flat ground using just their feet. This allows easy takeoffs and landings on wide cliff ledges and grassy areas.
Guano resistance
Thick skin on their feet protects Northern gannets against caustic guano burns. They can withstand the corrosive effects of accumulated droppings around the nest.
Aggressive defense
Northern gannets aggressively defend their nest sites from intruding gannets. Intense territorial disputes involve pecking, fencing with bills, and grappling.
Durability
Their sturdy bodies allow Northern gannets to survive routine skirmishes with neighbors. They come away unharmed after violent territorial fights.
Camouflage
Their pale coloration serves as camouflage against the sea and cliffs, hiding incubating gannets or chicks from aerial predators.
Nesting season
The breeding season of Northern gannets varies slightly across their range:
April to September
Northern gannets in Canada and New England usually arrive at colonies in April. They lay eggs beginning in May and the chicks fledge from July to September before fall migration.
March to October
In the UK and Iceland, Northern gannets begin nesting activities as early as March. Chicks may not fledge until October before migrating south.
Extended occupancy
Northern gannets occupy breeding sites for extended periods before and after actual nesting and egg-laying. Non-breeding juveniles may overwinter at colonies.
Winter nest maintenance
Northern gannets perform nest repair and reinforcement during brief winter visits before spring breeding. This maintains their territory until the next nesting season.
Slow maturation
Northern gannets do not begin breeding until 4-5 years old. Immature birds gain experience at colonies by visiting for a few years before their first nesting attempt.
Threats and conservation
Northern gannet populations dropped sharply in the late 19th and early 20th century due to hunting, egg harvesting and habitat destruction. Their numbers have rebounded thanks to conservation measures:
Legal protections
Northern gannets today receive legal protection in the US, Canada, UK and Europe. This bans hunting, egg collecting and disturbance of nesting colonies.
Reduced persecution
With legal protections, Northern gannets are no longer persecuted as threats to fisheries. Their plunge-diving fishing habits once made them unpopular with human fishermen.
Protected colonies
Many major Northern gannet nesting sites now lie within nature reserves or designated protected areas, shielding colonies from development or disruption.
Increased fish stocks
The recovery of fish populations like herring and anchovy may have improved Northern gannet feeding and breeding success in recent decades.
Habitat loss
Coastal development near colonies could reduce available nesting habitat. Tourism and recreation can disturb protected sites if not properly managed.
Climate change
Rising sea levels and increased storm activity may gradually degrade important Northern gannet nesting cliffs and islands.
Pollution
As fish-eating seabirds, Northern gannets are vulnerable to bioaccumulation of marine pollutants like PCBs and mercury. Toxins could impact reproduction.
Conclusion
Northern gannets are specialized cliff-nesting seabirds of the North Atlantic. They breed in dense colonies on remote rocky islands and sea cliffs offering protection from weather and predators. Northern gannets utilize their adaptations for ground nesting, aggression, and cliffside gripping to thrive at packed nesting colonies. Legal protections and reduced persecution have allowed Northern gannet populations to recover from past declines. However, they face potential threats from climate change, habitat loss, pollution and disturbance. Careful management and monitoring of existing Northern gannet colonies will be key to their continued success. Ongoing research on their unique nesting behavior continues to provide ornithologists with valuable insights into the biology of gannets and other seabirds.