Panama snack stop

They generally follow the same route as it is the path of least resistance: follow mountain ranges, stay over land. Like most raptors, Swainson's hawks migration paths are land-based: not just so they can roost at night, but mainly to benefit from the thermals and updrafts to keep them aloft. That reduces the need to flap wings, and thus their energy spend – even though the trip will take longer that way.

As this clip demonstrates, the land-migration imperative means the Central American isthmus is a hotspot for bird migration. Indeed, Panama and Costa Rica are favorite destinations for bird watchers, when the season's right. A bit to the north, Veracruz in Mexico is another bird migration hotspot.

It's thought most hawks don't eat at all on migration. This clip shows an exception to that rule: on the way back, one bird takes an extended stopover of a couple of weeks in Panama, probably spending its time there foraging for food.

So, when they finally arrive in northern Argentina, after 6 to 8 weeks' migration, the hawks are pretty famished. Until a few decades ago, they fed on locusts. For their own reasons, local farmers have been getting rid of those. The hawks now concentrate on grasshoppers, and basically anything else that's edible.

For first-time visitors, finding what they need is not easy. Three of the five dots go dark. These birds probably died from starvation. But two birds thrive: they roam the region until winter rears its head in South America, and it's time to head back north again, where summer is getting under way.

Both dots make it back across the border, but unfortunately, right at the end of the clip, one of the surviving two birds expires.

Harsh, but not unusual

While a one-in-six survival rate may seem alarmingly harsh, it's not that unusual. First-year mortality for Swainson's Hawks is between 50% and 80%. Disease, starvation, predators and power lines – to name just a few common causes of death - take out a big number.

Only 10% to 15% of the young 'uns make it past their third or fourth year into adulthood, but from then on, annual survival rates are much better: around 90%. Adult Swainson's Hawks can expect to live into their low teens. There's one documented example of a female Swainson's Hawk in the wild who was at least 27 years old (and still nesting!)

The Californian population of Swainson's Hawks plummeted by about 90% at the end of last century but is now again increasing well. The monitoring project that produced this clip has been going for about four decades but is seeing its funding dry up. Check them out and consider supporting them (see details below).

Not all migrating birds shun the ocean. Here's an incredible map of an incredible migration path that's even longer than that of the Swainson's hawks.

In February 1995, a red knot (Calidris canutus rufa) in Tierra del Fuego (southern Argentina) was banded with the tag B95. That particular bird, likely born in 1993, was recaptured at least three times and resighted as recently as May 2014, in the Canadian Arctic.

B95 is more commonly known as 'Moonbird', because the length of its annual migration (app. 20,000 miles; 32,000 km) combined with its extreme longevity (if still alive, it's 25-26 years old now) means its total lifetime flight exceeds the distance from the Earth to the Moon.

As many other shorebirds do, the red knot takes the Atlantic Flyway hugging the coastline and crossing to South America via the ocean.

B95 has become the poster bird of conservationists in both North and South America. A book titled Moonbird: A Year on the Wind with the Great Survivor B95 (2012) received numerous awards, B95 has a statue in Mispillion Harbor on Delaware Bay and the City of Rio Grande on Tierra del Fuego has proclaimed B95 its natural ambassador.

Perhaps one day the nameless Swainson's Hawks in this clip, fallen in service of their ancestral instincts – against the odds of human increasing interference – will receive a similar honor.