“The female whale or dolphin, in her role as mother, is the linchpin of cetacean population and behavioral biology”, Whitehead and Mann, 2000.
Seventy miles from land, the Bank is a remote but shallow area and seasonal home for almost 5,000 whales each winter and early spring. Humpback whales are a migratory species, feeding during the summer at high latitudes and traveling 1,500 and more miles south each winter to warmer waters to mate and to give birth.
There is much still unknown about reproduction in humpback whales. In recent years genetic studies have provided more detailed insights but for a long time evidence was based on whaling records and top-side observations, limited in their inability to even discern males from females. And while photographs appear to show mating and birth in Pacific populations, on the Silver Bank no one – to date – has captured photographic evidence of either.
But while we haven’t seen it we know it’s going on! Witnessing the thrill of competing males in rowdy groups and the tender beauty of new, days old humpback whale calves leaves no doubt in the minds of any visitor.
So here are a few notes on what we do we know about the female side of reproduction in humpback whales. More on the males in another post.
Humpback whales do not have periods.
Lucky things. But like all mammals they have estrus cycles, i.e they ovulate and have even been found to synchronize the timing of their estrus cycles.
But, pregnancy lasts nearly a year.
Females reach sexual maturity at 6-8 years of age. The typical pattern is: get pregnant in the Caribbean one winter, travel north for the summer and back down the next and have the baby. Their gestation period, aka pregnancy, lasts about 11 months. Newborns stay with their mothers for a year or so, so calves will be back down the next winter with mum but may wean any time thereafter.
Calves are 12- 15 feet long at birth and weigh around a ton.
Okay, so they are whales after all (an adult female averages 40 feet and 40 tons) but that’s still a whopper! At birth, they are around 30% of their mother’s length, if just a fraction of their weight. It is thought that they are positively buoyant at birth, and they can swim, but are helped to the surface for their first breath. Calves enter the world tail first and the placenta easily dislodges and floats away. Newborn calves seen on the Silver Bank are a very pale, soft gray in color, darkening up within days as the melanin develops in their skin. We still don’t know much about the actual birth event for humpbacks on the Silver Bank. Does it take place at night? Are females alone? How long is their labor?
But there’s only one of them.
Humpbacks are uniparous, in other words they give birth to just one baby at a time twins are very rare, less than 1% of births.
Nursing calves drink around 50 gallons of milk per day.
Aside from how amazing it is to witness a baby humpback nursing, the whole lactation system is pretty interesting. With 40% fat content this yogurt-like milk is incredibly calorie rich, five times that of human breast milk. Calves do not ‘latch on’ and suckle in the human sense but some do show wear in the rostrum (nose) areas from positioning on their mother where milk is somewhat squirted in by compressor muscles in the mammary glands.
The incredibly high energy demands of pregnancy and lactation at a time of prolonged fast is just one of the many reasons whale watching on the Silver Bank must be and is carried out with the utmost sensitivity to the animals.
Moms have a lasting influence.
Genetic studies undertaken in recent years have shown that groups of whales observed associating on feeding grounds are in fact related through the maternal line. It makes sense and has been born out in the lab – mothers pass on their life lessons on feeding and such to their calves so these small groups of possibly half siblings or cousins were reading from the same genetic and experiential textbooks, so to speak. Many fascinating questions still remain…how are they communicating with each other? How closely are the groups related and working together?
While the males play no part in upbringing.
Perhaps no surprises there! But more on the testosterone fueled side of the coin in our next post.
It’s an honor to spend time on the Silver Bank as quiet observers during this profound time of life for north Atlantic humpback whales. Clearly reproduction is a fascinating part of their ecology with many unanswered questions. We hope science continues to provide insights that help us better understand and protect these amazing animals.
References and further reading
Cetacean Societies: Field Studies of Dolphins and Whales. Eds. Mann, J., Connor, R.C., Tyack, P.L., and Whitehead, H. University of Chicago Press, 2000
The Influence of Maternal Lineages on Social Affiliations Among Humpback Whales (Megaptera novaeangliae) on Their Feeding Grounds in the Southern Gulf of Maine. Weinrich., M.T., Rosenbaum H., Baker, C.S., Blackmer, A. L., and Whitehead, H. Journal of Heredity, 97(3), pp. 226-234. 2006
Review of Baleen Whale (Mysticeti) Reproduction and Implications for Management. Lockyer, C. H., Report to the International Whaling Commission, Special Issue 6, 1984
Reproductive Histories of Female Humpback Whales (Megaptera novaeangliae) in the North Pacific. Baker, C. S., Perry, A., Herman, L.H., Marine Ecology Progress Series, 41 (103-114), 1987