Field notebook
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Field notebook
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Theme trail
This is a live full-text trail through published facts, not a fixed marketing category.
Bogong moths fly up to a thousand kilometres to alpine caves they have never visited. Flight simulator experiments showed they combine a magnetic sense with visual landmarks, and that scrambling either one leaves them unable to hold a course.
The red admiral was long treated as an annual immigrant to Britain that could not survive the cold season. Records of adults active in midwinter and of overwintering success have accumulated as winters have warmed, changing how the species is classified.
No individual green darner completes the annual round trip. Isotope work on museum and field specimens showed a migratory generation flying north, its offspring flying south, and a third, non-migratory generation overwintering in the south before the cycle restarts.
The Atlantic striped bass fishery crashed in the early 1980s. Coordinated state moratoria and coastwide rules under a federal backstop rebuilt the stock within about a decade, making it one of the clearest cases of a deliberate fishery recovery.
Unlike frog tadpoles, common toad larvae carry unpalatable skin compounds. This lets the species breed in deeper, fish-holding ponds where frogspawn would be eaten, and explains the different ponds the two use.
The quills detach on contact, not in flight. Each one is loosely rooted and barbed at the tip, so a slap of the tail plants dozens into an attacker, and the microscopic barbs make them far harder to pull out than to push in.
Photographic sequences analysed in 2013 showed Todarodes pacificus leaving the water under jet power, then spreading its fins and arm membranes into aerofoils and gliding for tens of metres above the surface before folding them and re-entering.
In autumn, Caribbean spiny lobsters form marching lines of up to sixty animals, each keeping contact with the one ahead using its antennae. The formation reduces drag and appears to make the group harder for predators to attack.
This skua breeds farther south than almost any other bird, and individuals have been seen at the geographic South Pole itself, hundreds of kilometres from open water and from any possible food source, apparently while ranging over the ice sheet.
Reindeer detect light down to about 320 nanometres, well below the human limit. In snow, which reflects ultraviolet strongly, this turns lichen, urine and wolf fur into dark shapes against a bright field.
The passenger pigeon may have numbered in the billions in the early nineteenth century. Within about fifty years of intensive commercial hunting and forest clearance it was gone from the wild, and the last captive bird died in 1914.
Radar and trap records show that migrant hoverflies, dominated by the marmalade hoverfly, arrive over southern Britain in numbers estimated in the billions each year. Their larvae eat aphids on arrival, making the migration a large and unmanaged pest-control service.
One of the largest freshwater fishes in the world does not hunt. Adult Mekong giant catfish lose their teeth and barbels and feed on algae and plant matter scraped from the riverbed, growing to nearly 300 kilograms on a diet with no meat in it.
The hummingbird hawkmoth hovers at flowers, hums audibly and darts between blooms, and is routinely reported as a hummingbird. No hummingbird lives anywhere in Europe today, and none has for tens of millions of years. The resemblance is convergence on the same physical problem.
Tracking devices fitted to Arctic terns revealed round trips far longer than the straight-line distance suggests, because the birds loop and detour with the winds. Annual totals above seventy thousand kilometres have been recorded, and some individual routes exceed ninety thousand.
Nightingales sing round the clock, but the celebrated nocturnal song has a narrow purpose. Males that have not yet attracted a mate do most of the singing through the dark hours; once a female settles with them, night singing usually falls away or stops.
It no longer feeds by pumping and straining water. Tiny hooked spicules covering its branches snag passing crustaceans like burrs, and the sponge then grows a membrane over the trapped animal and digests it where it hangs.
The image of lemmings hurling themselves off cliffs comes largely from a 1958 Disney documentary in which the animals were driven off a bank for the camera. Real lemmings disperse when crowded, and some drown attempting water crossings.
Wartime sonar operators found an echo layer that seemed to be the sea bed, except that it rose towards the surface each night and sank again by day. The layer turned out to be living animals, lanternfishes prominent among them.
Sanderlings chase each wave back down the beach and retreat ahead of the next. The timing is not play: the few seconds after water drains is when buried prey is closest to the surface and the sand is soft enough to probe quickly.
The European eel's breeding grounds in the Sargasso Sea were inferred from larval sizes a century ago, but not until 2022 did satellite tags follow adult eels the whole way there.
All the males in a breeding population sing broadly the same song, and that song is periodically replaced wholesale by a new one imported from the west. The replacement has been tracked moving from Australia across the South Pacific over several years.
Great whites are regional endotherms. A lattice of intertwined arteries and veins traps the heat their swimming muscles generate, holding the core of the body several degrees above the surrounding water and letting the shark hunt in cold seas.
Migratory tree bats die at wind facilities in numbers that outstrip resident cave species by a wide margin. The reason is not that turbines are hard to detect: evidence suggests the bats are attracted to the tall structures rather than blundering into them.
The rufa red knot times its stop in Delaware Bay to the spawning of horseshoe crabs. The eggs are soft and abundant enough for a bird to nearly double its mass in a fortnight, which is why a crab harvest thousands of kilometres from the Arctic affects Arctic breeding.
Every night a vast layer of small fish and squid rises toward the surface, and every dawn it sinks again. Bigeye tuna go down with it, spending daylight hours in cold, dim water hundreds of metres deep that other tropical tunas avoid.
Tracking shows snowy owls do not follow fixed migration routes. Individuals shift hundreds or thousands of kilometres between years, breeding wherever lemmings are abundant, and some winter far out on Arctic sea ice rather than moving south.
In the Serengeti, the great majority of wildebeest births fall inside a window of roughly two to three weeks. The synchrony floods predators with more calves than they can take, and a newborn is standing within minutes.
No single common green darner completes the round trip between northern breeding ponds and the southern wintering grounds. Isotope work on wing tissue indicates that the annual cycle is carried by a relay of roughly three successive generations, none of which retraces its own outbound flight.
Bobolinks leave hayfields in Canada and the northern United States and winter in the grasslands of southern South America, a round trip on the order of twenty thousand kilometres. Individuals return to the same breeding fields across successive years.
A young halibut is a symmetrical, upright larva with an eye on each side. During metamorphosis the left eye migrates over the top of the head to join the right, the skull remodels, and the fish tips over to live on its blind side.
There is no vaccine for Dracunculus medinensis and no drug that reliably kills the adult. Human cases have nonetheless fallen from millions a year in the 1980s to fewer than twenty, using water filtration and case containment alone.
The Lyme bacterium lives in a tick's midgut and must migrate to the salivary glands before it can be passed on. That relocation takes time, which is why the risk from a blacklegged tick rises sharply after roughly a day and a half of feeding.
In many north-temperate songbirds only the male sings, and the female stays silent. The northern cardinal breaks that pattern: females sing complex, learned songs from the nest area, sometimes trading phrases with their mate in a structured exchange.
A widely repeated claim held that shark decline released cownose rays, which then wrecked Chesapeake shellfish. Later analysis found the ray's diet, reproduction and population history could not support the story, but culls had already been encouraged.
In the Interlake region of Manitoba, red-sided garter snakes gather in limestone sinkholes each autumn in numbers reaching the tens of thousands per den. They emerge together in spring into some of the largest mating aggregations known in any vertebrate.
Every Pacific salmon dies after spawning. The Atlantic salmon does not necessarily: a minority of spawned-out fish, called kelts and overwhelmingly female, drop back downstream, recondition at sea, and return to the river to spawn again.
Tagging in the North Atlantic has followed individual blue sharks from the eastern seaboard of North America to Europe and Africa, with movements of several thousand kilometres. The species is the most widely distributed shark in the world.
In United States labelling practice, white meat tuna refers to one species. Albacore's flesh is markedly paler than that of other commercial tunas, and the term is reserved for it; other species must be sold as light or dark tuna.
In 1822 a white stork was shot in Germany carrying a long African spear through its neck. It had flown home wounded, and the arrow it carried settled centuries of speculation about where Europe's birds went in winter.
In the early 1940s the entire wild migratory population of whooping cranes was down to about fifteen birds. All wild whooping cranes alive today trace back to that remnant, which is why the species carries so little genetic diversity.
Swallowed Ascaris eggs hatch in the intestine, but the larvae do not stay. They burrow into blood vessels, pass through the liver and heart to the lungs, climb the airway and are swallowed a second time before maturing.
Pressed by a predator, a mule deer stots: it launches off all four feet at once and lands on all four, bounding across broken ground. It is slower than a flat run, which is what makes the behaviour interesting.
Born on drifting ice that may not last, a harp seal pup nurses on milk of extraordinary fat content, roughly triples its birth mass in under two weeks, and is then abandoned to live on that stored blubber while it learns to swim.
The Sargasso Sea spawning ground was inferred a century ago from the sizes of drifting larvae, not from seeing eggs laid. Satellite tagging has now tracked adults toward the area, but a wild European eel spawning has still never been directly observed.
The male bed bug does not use the female's reproductive opening. He drives a sharpened organ straight through her abdominal wall and injects sperm into the body cavity, from which it migrates to the ovaries. The female has evolved armour at the target site.
The Canada goose is a symbol of migration, yet large numbers no longer migrate. Resident flocks, seeded partly by mid-century restoration releases, now live year-round on the mown lawns and ice-free ponds that cities supply.
Saguaro and organ pipe cactus blooms open after dark, smell faintly of rotting fruit and hold nectar deep in a sturdy tube. Those are traits shaped by bat pollinators, and the lesser long-nosed bat is the one they were shaped for.
Each spring the great majority of North America's sandhill cranes funnel into a short stretch of the Platte River in Nebraska. They spend weeks feeding on waste grain to build fat for the flight north, then leave almost at once.
Macrotus californicus has unusually large eyes for a leaf-nosed bat and can locate prey in dim light with its sonar effectively switched off. In experiments it caught insects using vision alone, which few echolocating bats manage.