In the early 1970s, the nesting site of the marbled murrelet along the Pacific Coast was one of the great remaining bird science mysteries of North America. How could a bird that numbered in the thousands when seen out at sea not have an obvious nesting place? The mystery wasn’t solved until 1974 when a maintenance worker in Big Basin State Park near Santa Cruz in central California was climbing in an old growth redwood tree less than a half mile from the park’s main visitor center. Near the tree top, he saw a fluffy spotted nestling about the size of a robin sitting on a very large branch. Strangely, the chick had webbed feet. He took a picture of it and showed it to bird experts. Lo and behold, the nesting habitat of marbled murrelets was finally discovered––coastal old growth coniferous forests of the Pacific Northwest.
With the discovery of a murrelet nest in a tree, a major evolutionary leap in seabird biology was revealed. Most animals stick to a life style similar to other closely related species. Murrelets belong to the auk family (Alcidae) of birds that includes puffins, murres, and guillemots. All other alcids nest on isolated rocky islets or cliffs. But somewhere in the far past, a few murrelets’ ancestors decided that those giant woody green things just inland off the coast made pretty good nest platforms too. When that happened, a seabird became a forest bird.
To become forest birds, marbled murrelets had to develop adaptations not typical of seabirds. Coloration was one. Most seabirds are white on the bottom to blend in with the surface of the ocean when seen from below and dark on the back to blend in with the surface of the ocean when seen from above. During the non‐breeding season, murrelets hold to that pattern. But during the nesting season, they turn reddish brown all over with a marbling of white spots, perfectly blending in with the sun dappled shadows of the redwood canopy. The chicks are similarly well camouflaged. Murrelet eggs are also perfectly suited to their canopy environs, colored jade green with dark speckles.
Another adaptation from ocean to forest has to do with parental arrivals and departures from the nest. Murrelets only come inland from the sea during the low light hours just before sunrise or just after sunset. This lowers their chances of being seen by a predatory bird that hunts during daylight. Once at the nest, one adult either feeds the chick and leaves as quickly as possible or makes a quick exchange with its partner if an egg is being incubated. The adult won’t return for a full 24 hours, leaving the incubating adult or nestling to sit on the nest in absolute stillness, trying to stay as hidden as possible. After a month of egg incubation and a month of feeding their rapidly growing chick, the murrelet parents abandon their chick to its fate.
The chick, now half again heavier than its parents, needs every gram of that extra fat to undergo a simultaneous molt lasting just a few days. The chick loses all its spotted nestling down and replaces it with black‐and‐white subadult feathers in one fell swoop, a massively energetic process. The now boldly‐patterned nestling stands out in a forest setting, but the soon‐to‐be fledgling is wonderfully cryptic for an ocean setting. The fledgling leaps off the large branch that has been its only home and takes its first flight. Alone. On instinct only, the newly fledged bird must navigate up and out of the massive trees and westward to the ocean. If lucky, it will land just outside the surf zone, and dive beneath the sea where it will fly underwater like a penguin, chasing prey like sand lance, herring and anchovy.