Elizabeth Bassett, contributor
Women groan at the thought of giving birth to an 11- or 12-pound baby. Imagine a gray whale calf, weighing at birth 1,100 pounds and 15 feet long. Ouch! Gray whale mothers produce rich milk, 50 percent fat, and a nursing calf can gain several pounds an hour and up to 200 pounds in a day, while swimming the entire time.
On a recent afternoon in Baja California, we trailed, at a safe distance, a mother gray whale and her young calf. They swam slowly and surfaced frequently to breathe. An adult can dive for up to five minutes, but a calf must breathe more frequently. Adults may host hundreds of pounds of barnacles that appear as yellow-orange splotches on their mottled gray and white skin. When a calf is born the mother whale’s barnacles release larvae, some of which settle onto the calf for life. The calf will soon sport its own barnacle crust.
Mother whales scarcely eat during their migration to and from warm waters where they give birth. Between swimming and nursing, the mothers may lose up to a quarter of their total body weight, which is about 45 tons, before returning to the cold, nutrient-rich waters of the north to feed. Perhaps this is why gray whale females outweigh their male counterparts by several tons. (“Honey, do I look fat beneath these barnacles?”)
When a gray whale calf is several months old the real dangers await as mother and baby attempt to swim from Baja California to the Bering Sea, the longest known mammal migration. The pair leave the protected waters of the nursery to swim north, hugging the Pacific coastline. Orca or killer whales travel in family groups of a half dozen or more. They can gang up on a calf, attempting to hold it underwater until it drowns. A mother’s best defense is to thrash her enormous (and heavy) tail to drive the Orcas away. Then she and her calf dive deep and swim as fast as they can in hopes of out-swimming the Orcas.
This January the whales were late in arriving along the coast of Baja. The ocean water is warmer than usual, so the mothers were slow to arrive in the safe southern waters for birthing. Water temperatures notwithstanding, the seasons change and instinct will soon impel mother and calf to begin their long migration north. By March or April they will start their swim to northern Alaska, whether or not the calf is strong enough to withstand predation.
Meanwhile, back on land…
The Sonoran desert of Baja bristles with cacti. In order to survive in such a hot, dry place, where it may not rain for years at a time, cacti have many adaptations. Waxy or resinous coatings minimize evaporation, as do thorns and tiny leaves. Spines and hairs, which break up the sun’s rays, may replace leaves entirely. In the absence of leaves some cacti photosynthesize along stems and branches. During dry periods deciduous cacti shed leaves and then re-grow them quickly when rain falls.
All cacti have inner structural supports, including wooden rods or staves, which allow the plant to expand quickly when water is available. By shrinking their vertical ribs some cacti can sustain a 60-70 percent loss of their water mass, persevering for several years without rainfall. To capitalize on scarce rainfall, cacti often have huge root systems close to the surface. While cacti grow in the driest of deserts, they also thrive in jungles and mountains, along coastlines and on grassy plains.
And in the air…
Ever heard of klepto-parasitism? Frigate birds are large sea birds that have evolved with long and delicate wings that can span eight feet while the bird’s total weight is only 3.5 pounds. They have lost their ability to dive into the water to catch fish, as crashing into the waves would shatter their bones. The solution: frigate birds follow pelicans, ospreys, gulls and other fish-eating birds and snatch prey from their beaks! This makes for some dramatic mid-air action!