Southbound Babies
Two Scientists Speak

Baby whale and Mom, heading south along California: Jan. 2006
Photo Tony Nichols
Each year, a few gray whale calves are born before their mothers reach the warm, calmer lagoons of Mexico's Baja Peninsula. How does being born in the open ocean during their mother's migration affect the calves? This question puzzles scientists. After all, it's tough to study what you can't see and keep track of. Here's what two scientists think about southbound babies:


Dr. Dave Rugh
Dave Rugh (say "Roo"), wildlife biologist with the National Marine Mammal Laboratory (NMML) in Washington state. Dr. Rugh and Kim Shelden of the NMML worked together to describe southbound gray whale calves seen passing on the migration trail near Carmel, California. Naturally they wonder about these babies' chances of survival compared to the babies born in the lagoons. It's hard to see a whale calf from shore, but shore-based observers in central California count calves each southward migration. Dr. Rugh says as few as four calves to as many as 60 have been sighted in a season during the past two decades. Many more new calves swm past without being seen.

Dr. Dave Rugh

Dr. Rugh told Journey North: "I wish I had an unequivocal answer to the question about survivability of gray whales born in the Baja lagoons versus those born while migrating. However, we do not have data on the percentage born within the lagoons, nor can we trace the fate of those that were born elsewhere. Adult whales have been observed leaving a lagoon and returning with a calf, so the lagoons are not critical for birthing as much as they may be advantageous as nurseries. The relatively protected, warm waters reduce heat loss in the calves. Many calves are born well north of the lagoons, so we can assume they have evolved the ability to survive birth at sea outside of the protection of the lagoons. So far we have not found any clear evidence that it is any worse to be born en route.

"Difficulties that gray whale calves may encounter outside of the lagoons are high waves (calves are vulnerable to drowning) and colder water (thermoenergetics can put an increased demand on their resources). Sharks and killer whales can kill gray whales both in and out of the lagoons, so it is not known how much of an advantage it is to be inside a lagoon to avoid predation."

Wayne Perryman

Wayne Perryman

Wayne Perryman is a biologist and gray whale calf expert with the National Marine Fisheries Service. Each spring he conducts the official gray whale cow/calf census for the U.S. government. Mr. Perryman says: "If a calf is born along the migration route, it will be required to migrate instead of just hanging around. This, it seems, would cause it to burn more energy. Calves are born skinny, with little or no insulative blubber layer, so they will also burn up some energy keeping warm. The water in the lagoons is not only warm, but the salinity (saltiness) is very high. Calves can float easily to the surface in the lagoon's high-density water, while calves born in the lower salinity waters along the California coast may have to swim to the surface, and the higher waves can make them more vulnerable to drowning. Storms may separate them from their mothers. Probably the most important disadvantage of being born along the migration route is that killer whales can find the calves. There are normally no killer whales in the lagoons, so it is a safer place if you are a calf."

Try This! Journal or Discussion Questions
  • In a two-column chart, list the facts shared by scientists in one column and their opinions in the other. Why is it difficult to know for certain about the survival rate of gray whale babies in each environment?
  • Paraphrase Dave Rugh's comments in your own words and tell a friend what this scientist thinks.
  • What do you think are the best conditions for a baby whale's birth and survival in its first months of life? Make a list based on the scientists' comments and your own ideas.

National Science Education Standards

  • Scientists develop explanations using observations (evidence) and what they already know about the world.
  • Organisms have basic needs. They can survive only in environments in which their needs can be met.
  • All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions in a constantly changing external environment.