Yesterday's Island Today's Nantucket
Nantucket
Science
Volume 40 Issue 2 • May 6-12, 2010
now in our 40th season

Naturally Born Mothers

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

With Mother’s Day right around the corner, I thought I would write about some of the maternal instincts inherent or, in some cases, relatively absent, in various creatures seen on and around Nantucket.  The amount of parental attention bestowed upon offspring is typically directly related to the amount of energy and time that went into producing that offspring.  With long gestation times and smaller broods, mothers tend to be more involved in the upbringing of little junior, whereas if you just produced 100-1000 eight-legged spider darlings, you can probably spare a few.  Hopefully these facts will help you appreciate your Mom even more.

As a member of the Nantucket Marine Mammal Stranding Team (nantucketstrandingteam.org), we often get worried calls from folks who see juvenile gray seals (Halichoerus grypus) hauled out on shore with no adult in sight.  What appears to be the animal equivalent of leaving a baby on the doorstep is simply the natural progression of that juvenile through its life cycle.  Gray seals nurse for only 21-28 days after they are born and their mother’s milk contains some of the highest lipid (fat) concentrations in the animal world, which helps to fatten up the sausage-like pups.  The mother is very protective of her single pup on land; but she is also preparing to mate again with a male immediately (which mystifies me), and after the pup is weaned, the mother will leave the pup to feed, and upon return will recognize her offspring by its unique smell.  Once they wean, the pups live off blubber reserves and go to sea at about five to eight weeks of age.  At this time, they are on their own.  So a hauled-out juvenile gray seal is not abandoned, but often warming up and taking a break from a busy day of eating and swimming.

You cannot spend much time on Nantucket without noticing the cottontail rabbits running around. The Eastern Cottontail (Sylvilagus floridanus, J.A. Allen, 1890) is a New World cottontail rabbit, a member of the family Leporidae. It is one of the most common rabbit species in North America.  Bunny moms fall midway on the spectrum of parental care.  They build a very cozy nest in the ground, which is made by excavating a small hole and hiding it under a layer of grass and soil, forming a lid to the nursery cavity. Both lid and nest are lined with fur and steam rises from the nest if the “lid” is lifted to see the furry baby bunnies (known as kits or kittens) snuggled together.  After the female has given birth to her offspring, she can mate again immediately, so she is off to do what we expect most bunnies to do.  She will come back to the nest to feed the young twice a day for the first three weeks, usually at dawn and dusk; she will not visit the nest in the daytime in order to avoid alerting predators to its location.  As she is practically an absentee mother, her milk is one of the most nutritious of all mammals. The female gives birth about a month after mating.  She has between one to nine babies, although she usually will have four to five young.  The babies are weaned after about three weeks and leave the nest after about seven weeks.  Females can have three or four litters a year.  Eastern cottontails are ready to mate when they are three  months old. Their lifespan is on average three years although they can live much longer in captivity.

White tailed deer (Odocoileus virginianus) are also abundant on Nantucket.  White tailed deer weigh between 125-300 lbs and reach sexual maturity at about two years of age.  The mating or rutting season runs from approximately October to December and the typical gestation period is about 200 days.  At birth, fawns are spotted with white and weight between 3 and 6 lbs. A doe can be expected to produce fawns up to the year of her death and she may live to ten out in the wild. Under favorable conditions, most adult does should have two fawns.  Frequently triplets and occasionally liters of up to four have been reported.  Generally does reach peak bodyweight by 3½ years and bucks reach peak bodyweight at 4½ years. (www.whitetaildeer-management-and-hunting.com/whitetail-deer-facts.html)

Deer are pretty attentive mothers. In mid to late spring, the doe will give birth to her fawns. Fawns can walk at birth and in a few days they will begin nibbling on vegetation. They are weaned from their mother in about 8-10 weeks. Young females usually stay with their mother for two years while young males leave sooner, after about one year. The female white tailed deer is very protective of her young. When searching for food, the mother will hide her offspring until they are old enough to follow her, about 4 weeks of age. The fawn will lie quietly on the ground and its spots will help camouflage him or her from predators. The white tailed deer will raise its tail to expose the white underside to warn other deer of danger. The female deer will raise it to make it easier for her young to follow her. Read more about these creatures at: www.brighthub.com/environment/science-environmental/articles/48142.aspx

Another familiar ACK resident, the common snapping turtle (Chelydra serpentina serpentina), works hard to find a nursery for her young, but then she turns over the juvenile upbringing to Mother Nature. Females travel over land to find sandy soil in which to lay their eggs, often some distance from the water, nests up to a mile away has been recorded in some instances. After digging a hole, the female typically deposits 25 to 80 eggs each year, guiding them into the nest with her hind feet and covering them with sand for incubation and protection. Incubation time is temperature-dependent, ranging from 9 to 18 weeks. In cooler climates, hatchlings may overwinter in the nest, although that doesn't always insure survival in a frigid winter. Females produce, at most, one clutch per year, with some females apparently skipping some years. They lay spherical, hard-shelled eggs that average 1.1 in (2.8 cm) in diameter and 0.4 oz (11 g) in mass. Egg size does not seem to increase significantly with female size. Clutch size is highly variable, ranging from six to 109, averaging about 32 across the range, and is positively correlated with female body size, latitude, longitude, and elevation (the largest clutches are laid in western Nebraska). Incubation in nature requires 55–125 days (more typically 75–95) depending on nest temperature (development being faster at higher temperatures) and geography (incubation times being longer in the south). Hatchling snapping turtles usually emerge from the nest in the late summer and fall (August to October) and move directly to the water. Hatchlings in northern populations that do not emerge in the fall before the onset of cold weather almost never survive the winter, probably because of their low tolerance of subfreezing body temperatures. High and low incubation temperatures result in the production of all-female offspring, and intermediate temperatures produce all males. Because their clutches are so large, eggs in different parts of the same nest may produce different sex ratios, e.g., all females at the top and all males at the bottom. Here on Nantucket you are most likely to see juveniles trying to cross the road to get to water as early as August.

Pseudacris crucifer, or spring peepers are members of the Hylidae (true tree frogs) family and are native to eastern North American. You can hear the males calling for their mates all over the island. Females are looking for the largest males and presumably the loudest “peeps”. Spring peepers exhibit size-selective mating which means the larger males breed more frequently. The spring peeper is usually about three years old before it reaches the breeding stage. Research indicates that the females are really looking for the males who have grown bigger faster, not necessarily the oldest males. After flowers and rings are exchanged, the females become gravid with viable eggs and they deposit their eggs in a watery spot preferably in a shallow location with a minimum of predators like fish. The spring peeper breeds between the months of March to June, and deposits around 900 eggs (although they can deposit up to 1000) that are hidden under vegetation or debris. It takes about 1-2 weeks for the tadpoles to emerge from the eggs and then from 2-3 months for them to complete their transformation from tadpoles to frogs. After laying the eggs, mom is out of the picture.

This Mother’s Day, (May 9), please come join us for the kick off of the Nantucket Family Adventure taking place from 12-2 at the Linda Loring Nature Foundation at 110 Eel Point Road. This outdoor family activity is a collaborative effort from island scientific and conservation groups that encourages families to get outside and explore different areas of the island over six-weeks. There will be a variety of free and fun activities like nature walks and games at the kick off. For details and to register visit: www.mmo.org/education/current-events.html

 

Nantucket’s most complete events & arts calendar • Established 1970 • © © 2017  Yesterday's Island • yi@nantucket.net