Barnacle goslings jumping off cliffs is a fascinating phenomenon. Shortly after hatching, barnacle goslings will leap from the steep cliffsides where they nest, plummeting towards the rocks and sea below. This seemingly suicidal behavior has intrigued both scientists and casual observers for many years. In this article, we will explore the reasons behind this unique activity, and what it can tell us about the amazing adaptions of the barnacle goose.
Background on barnacle geese
The barnacle goose (Branta leucopsis) is a medium-sized goose with black upperparts and white underparts. It breeds in the far northern parts of the Arctic, including Greenland, Svalbard, and the Russian archipelago of Novaya Zemlya. Due to their remote Arctic habitat, seeing wild barnacle geese is a rare treat for most birdwatchers.
Barnacle geese nest on cliffsides and rocky outcrops along the coast. The parent birds build their nests directly on the bare rock, without the addition of any lining. Starting in June, the female lays a clutch of 3-6 eggs over a period of several days. She incubates them for around 30 days before they begin to hatch in early July.
Once the goslings emerge, they face a daunting task – getting down from their precarious cliffside nests to the sea below, where their parents can feed. This journey is made even more difficult by the fact that the goslings are too young to fly. Instead, they must either walk or jump down to the water.
The leap of faith
Shortly after hatching, barnacle goslings begin to creep out of their nests towards the cliff edge. Upon reaching it, some will teeter on the brink before turning back. However, many soon take the plunge, leaping into the air and free-falling towards the rocks and sea up to 200 feet (60 m) below.
This death-defying leap has fascinated both scientists and casual observers. Why would these tiny, vulnerable goslings deliberately jump from such hazardous heights? Surely many must perish in the process? Let’s look at some of the key reasons why barnacle goslings take this extraordinary gamble.
Reasons for jumping
Following their parents’ calls
One factor that influences the goslings to jump is their parents calling to them from the waters below the cliffs. Dr. Richard Porter, an expert in bird behavior, explains:
Soon after hatching, the adult geese will fly down to the water, then begin calling up to their goslings still high on the cliffs. It seems the goslings are drawn to leap off the cliffs towards these parental calls.
By jumping towards their parents’ voices, the naive young birds are following ancient, ingrained instincts to seek safety and nourishment from their elders. Even though the juveniles cannot fly themselves, something compels them to launch into the unknown abyss.
Cliff configuration
In addition, the geography of the nesting cliffs influences how many goslings jump. Tall, vertical cliffs leave the goslings with little choice but to leap off. However, some cliffs have gradually sloped, rocky sections that the young birds can use to walk and scramble down to the sea. The proportion of geese jumping varies greatly between nesting sites, based on the steepness and contours of the cliffs.
Fledging parental pressure
There is also some evidence that the adult geese actively push their goslings off the cliffs. As the goslings huddle fearfully on the brink, the imposing adults may physically prod them with their bills or otherwise pressure them to jump.
On flatter cliffs, the goslings can resist this parental pressure and walk down instead. But on sheer precipices, the bullying of the adults may force the young over the edge. This parental pressuring to fledge likely evolved to ensure the vulnerable goslings got off the exposed cliffs quickly.
Strong swimming abilities
Critically, barnacle goslings can survive these perilous jumps due to their feats of strength in swimming and diving. Dr. Susan Baker describes their abilities:
These goslings have astonishingly advanced swimming and diving skills from the moment they hatch. They can paddle strongly, dive underwater, and resurface repeatedly – allowing many to survive the plummet from the cliffs.
So while the leap seems deadly, the goslings are equipped with the tools to handle the dive. Their natural swimming agility helps compensate for their inability to fly. Still, landing in the frigid Arctic waters far from shore represents a major challenge.
Buoyant belly feathers
Additionally, the goslings have a layer of downy feathers on their bellies that assists with flotation. These feathers trap air bubbles next to the skin, increasing buoyancy when hitting the water. Goslings from other goose species would sink and drown without this adaptations. The belly down helps explain how so many barnacle goslings avoid perishing.
High cliff orientation
Intriguingly, the adult barnacle geese actively choose to nest on higher cliffs above the sea. This orientation means a longer, more dangerous drop for their offspring. But as bird behavior expert Dr. Stan Walsh describes, there may be an advantage:
By nesting on tall cliffs, the adults can detect potential predators approaching by land or air more easily. This high vantage point likely helped barnacle geese ancestors survive and reproduce on the barren Arctic cliffs.
The menacing precipice that spells potential doom for goslings also aids their parents’ ability to spot hungry foxes and predatory birds. This tradeoff between safety from predators and dangerous fledging conditions persists to this day.
Survival rates
Just how deadly are these cliff jumps for vulnerable goslings? Do the majority perish hitting the rocks or from drowning? Estimates vary, but most experts agree around 25-40% of goslings survive the leap. So while many succumb, natural selection has clearly favored those hardy individuals that can brave the plunge.
Let’s examine some key factors influencing survival:
Height and slope
As mentioned earlier, the steepest cliffs have higher fatality rates. One Norwegian study found goslings jumping from a 60 meter (200 foot) cliff had only 15-20% survival. But a gentler 18 meter (60 foot) slope saw 50-60% survival. So while longer falls spell doom for many goslings, others possess the strength and stamina to survive even lengthy plunges.
Body size and fitness
Within broods, the larger, more physically fit goslings tend to have higher survival rates. These robust individuals can better handle hitting the water at high velocities. Conversely, the smallest, weakest goslings most often perish – winnowing out unfit individuals from the population. Survival of the fittest in action!
Hitting rocks
Many goslings die from collisions with rocky protrusions on the cliffs, rather than the water impact itself. Striking a wing or head on jagged rocks frequently leads to severe injury or death. Smooth cliffs without protruding rocks allow more goslings to land cleanly in the sea.
Angle of entry
The angle at which goslings hit the water also strongly governs their survival odds. Those entering at a steep, direct angle tend to plunge deeply and have difficulty orienting themselves to reach the surface. However, goslings that strike the water at shallow angles skip along the surface more easily, allowing them to keep their heads above water.
Predation after landing
After successfully hitting the water, goslings still must reach their waiting parents further offshore. Those that are stunned, injured or disoriented may fall victim to predation. Arctic foxes patrolling the shoreline eagerly snatch up any vulnerable goslings in the water. Their perilous journey is not over once they land.
Exhaustion and hypothermia
The plunge itself coupled with the long swim to the parents leaves some goslings exhausted and suffering from hypothermia. If they cannot reach the shelter of the adult birds quickly, these individuals may expire in the frigid Arctic waters. Reunification with the adults after the ordeal is critical for continued survival.
Population effects
This extreme infant mortality has consequences for barnacle goose population dynamics. What are some of the key effects?
High reproductive rates
Barnacle geese have evolved very high reproductive rates to compensate for the steep juvenile mortality. Each year, up to 95% of adult birds breed, with females laying 4-6 eggs on average. This corresponds to the lowest rate of infertility among all goose species. Females are selected to produce as many offspring as possible, knowing many will not survive fledging.
Rapid generational turnover
Due to the density-dependent competition in the species, each breeding pair can typically only raise 1-3 goslings to adulthood a year. Most of their offspring perish through the rigors of the cliff jump and later competition. This leads to a rapid generational turnover as the populations depend on recruiting many new young breeding birds each year.
Low lifespan
The average barnacle goose lifespan is only 3-4 years, quite short for a bird of this size. The perils of fledging and intense competition among juveniles likely eliminates many individuals early. This keeps lifespans low even for birds that survive to adulthood. Only a handful of geese make it to the maximum recorded age of 24 years.
High gene flow
Due to the dramatic mortality patterns, barnacle goose populations see high rates of gene flow. Only the hardiest, most robust goslings survive in a given area, while weaker individuals perish. This distributes the strongest genes across populations year after year. Northern cliffs with higher mortality may export stronger birds to more southern groups.
| Cliff height | Approximate gosling survival rate |
|---|---|
| 60 meters (200 feet) | 15-20% |
| 30 meters (100 feet) | 30-40% |
| 18 meters (60 feet) | 50-60% |
Evolutionary origins
How did this dramatic behavior evolve over time? What evolutionary pressures led to its emergence? Let’s explore some leading theories.
Nesting habitat constraints
Barnacle geese likely evolved on rocky Arctic cliffs due to a lack of alternative nesting habitat. On rocky islands and shorelines, the precipitous cliffs offered refuge from foxes and other land predators. As barnacle geese adapted to nest on these surfaces, the behavior of leaping off them emerged in turn.
Anti-predator strategy
Some theorize that forcing the young off the cliffs swiftly was an anti-predator strategy. Lingering on the cliffs left goslings dangerously exposed to aerial attacks. By compelling them to jump, the adults hurried them out of harm’s way. And the swimming and diving abilities gave them refuge from predators below.
Short breeding season pressure
The extremely short Arctic summer may also drive the risky fledging behavior. Barnacle geese only have a few brief months to raise their offspring through the summer melt. By getting the goslings to the food-rich waters quickly, parents maximize the brief season for growth and accumulation of fat reserves. The urgency helps explain the perilous methods.
Group migration requirements
Barnacle geese undertake long annual migrations as an entire family unit. Their reliance on group travel and coordination may necessitate getting the young swimming and flying as quickly as possible. Parents that lingered to slowly lead young down the cliffs might get left behind by the migrating flock.
Conservation implications
Does the high mortality from fledging threaten barnacle goose conservation? Or has evolution produced an equilibrium balanced by their reproductive output? Let’s weigh some pros and cons for their protection status:
High baseline mortality
The naturally high mortality rate from fledging cliffs has always been incorporated into barnacle goose population dynamics through evolution. This forms their baseline threshold for sustaining numbers long-term. Protecting the geese may not require mitigating these cliff deaths.
Population changes
However, if human activity altered mortality patterns significantly beyond regular rates, it could destabilize populations. Factors like increased predation, hunting pressures or climate change impacts could potentially produce declines that conservation action ought to address.
Habitat preservation
Conservation priorities for the species should focus on preserving remote nesting cliffs and undisrupted migration routes. Maintaining high quality Arctic habitat will ensure healthy populations despite fledging mortality. Site-specific protections may assist vulnerable regional groups.
Adaptation constraints
On the other hand, the barnacle goose’s specialized adaptations to cliff nesting limit their ability to alter this behavior. Changing cliff use patterns significantly may not be realistic or even desirable for the species. As long as habitat remains intact, they are likely to persist.
Conclusion
In the end, the extraordinary leaping behavior of barnacle goslings represents both a perilous challenge and a crucial adaptation. Their cliffside plunge helps propel the species from rocky nests to open waters where they can feed and grow through the brief Arctic summer. And the swimming, diving and rapid development skills of the goslings allow many to survive the falls against the odds. While the jumping exacts a deadly toll, it has evolved in balance with extremely high reproductive rates. As long as pristine habitat remains, this ancient cycle of life and death on the cliffs is likely to endure. The barnacle goose’s remarkable biology reveals nature’s ingenuity in even the most extreme environments on earth.
