The Homing Instinct: Meaning and Mystery in Animal Migration

  • Bernd Heinrich
Houghton Mifflin Harcourt: 2014. 9780547198484 | ISBN: 978-0-5471-9848-4

Animal migration is a wondrous thing. Driven by seasonal changes in daylight and other factors, an incredible array of organisms fly, creep or run through urban and other habitat-restricted areas on their way to or from richer spots for wintering, feeding or breeding. When you watch the movement of migrants (and I know birds best), you see the beauty of the individuals, and are privy to the performance of ancient commands dictated by genetic coding. It is often a species' most vulnerable moment. Human-driven and other shifts can occur too quickly for an individual to adjust: a bird that has flown all night looks down at the landscape that emerges at dawn, and seeks an accommodating wood that may or may not still be standing.

Semipalmated sandpipers (Calidris pusilla) on their annual autumn migration. Credit: Yva Momatiuk & John Eastcott/Minden Pictures/FLPA

In The Homing Instinct, biologist Bernd Heinrich explores the concept of 'home' — how organisms in a wide range of taxa, including insects, arachnids, amphibians, fish, birds and mammals, arrive at their destinations, construct or alter home territories, and live in them. He discusses the placement of nests according to geographic and site-specific factors; nest structure and hygiene; parasitism and feeding behaviour. In the telling, he relies on the latest scientific advances as well as his own field observations.

Despite the tens of thousands of human eyes trained on animal migrants, many elements of the migration period, such as routes and duration of travel, were difficult to investigate until the advent of satellite technology. This has shed light on astounding behaviours, and Heinrich discusses one of my favourite cases: the prodigious speed and endurance of the bar-tailed godwit (Limosa lapponica).

This long-billed, long-legged shorebird was known to nest in the Arctic and winter in Australia and New Zealand. In a 2009 study, transmitters were placed on 23 of the birds to track their flight paths. They revealed that the species can fly from Alaska to New Zealand in less than nine days without stopping, riding wind currents and expending half their body weight (R. E. Gill Jr et al. Proc. R. Soc. B 276, 447–457; 2009). (On the way north, the birds do stop to feed.)

Heinrich discusses at length how species such as sandhill cranes (Grus canadensis) and bees return to the places of their birth. But from an evolutionary standpoint, it is important for some individuals not to get homing quite right.

Take salmon. These fish use smell to find their streams of origin, as was corroborated by experiments in which they were raised in hatcheries and exposed to a particular chemical, then released into Lake Michigan. Each of their spawning streams was treated with one of the chemicals, and indeed 90% of the salmon selected the stream with the smell of home. It is likely that most of the remainder did not survive; possibly they selected the 'correct' waterway, but it had become unsuitable for spawning. However, some of these mostly suicidal explorer fish would have survived, by finding different, habitable streams. This is essential for the long-term survival of the species.

I think Heinrich could have left out the chapter 'Homing to the Herd', in which he switches his discussions from homing based on place to homing based on the flock. He sees the mass gatherings of the now-extinct Rocky Mountain locusts (Melanoplus spretus) as the home, even though they shifted from place to place. And in his treatment of the also extinct passenger pigeon (Ectopistes migratorius), which up to its demise in the late 1870s gathered in everything from pairs to aggregations of billions, he gets some important facts wrong.

It is true that passenger pigeons “were reputed to nest for most of the year wherever and whenever they found food”. But those so reputing were often hunters or dealers in the game-meat industry, who wanted to allay fears that the birds were disappearing. In any event, as the naturalist A. W. Schorger (whom Heinrich cites as a reference) made clear, passenger pigeons generally nested only once a year. Heinrich bases much of this discussion on a comparison with the mourning dove (Zenaida macroura); however, genetic work has shown the passenger pigeon to be much closer to a group that includes the band-tailed pigeon (Patagioenas fasciata).

Having said all that, this is an informative and fascinating book. In choosing to explore this elemental behaviour across such a vast range of taxa, Heinrich has written a work for which many will provide a home.