Subject: Common Dolphins

Jennifer D. Philips (
Sun, 26 Apr 1998 11:36:21 -1000

At 09:15 AM 4/26/98 -0400, you wrote:
>    Jen, My name is Andrew. I am working on a  research project about
>whales and dolphins. I was assigned the Common Dolphin  and all I have left
>to find are where are the bones in my dolphin, how much  blubber and how
>much hair, how it breathes, what does it use to breathe and what  steps in
>breathing, how much do they eat, how often to they eat, how do they  eat,
>where do they give birth, how many babies born at a time, what is baby's 
>weight, how many babies would mother have during whole life, how do they
>give  birth and hat primary organs help give birth. I hope this isn't too
>many  questions for you and I only want you to answer as much as you can.  
>                                              Andrew Bogorad age:9    

Andrew  - 

Wow!  That is a lot of questions!  First of all, I would recommend a great
book on whales and dolphins, called the Sierra Club Handbook of Whales and
Dolphins.  It offers great information about all species of whales and
dolphins, including your common dolphin.  But I will answer your questions
as fully as I can:

Where are the bones in your dolphin?  Most of the bones in a dolphin are
structured similarly to other mammals, and the skeletons of dolphins and
whales are very similar to each other.  If you have every seen a drawing of
the skeleton of other mammals, then you can imagine what the skeleton of
dolphins looks like.  There are some modifications, though.  For example,
the limbs are very reduced, especially the hind limbs, which are gone
entirely.  But the basic structure of the front limb is still the same.  If
you were to see the bones inside a dolphin's fin, you would see that they
look just like the bones in your hand.  Another modification is that the
back bone works differently:  it is fused so that the back of dolphins is
almost rigid (unlike ours, which is loose so we can bend over).

Blubber and Hair:  All cetaceans (whales and dolphins) have blubber to help
maintain a stable core-temperature, despite surrounding conditions.  The
blubber layer varies in thickness between species, and most dolphins,
including the common dolphin have a layer about 1 inch thick.  Common
dolphin calves are born with a few hairs around the tip of their rostrum
(their snout) , but later they lose that hair and remain hairless for the
rest of their lives.  Most likely, the hairs help calves find their
mother's nipples for nursing.

All about Breathing:  As you know dolphins are mammals and so must breath
air to survive.  Fish don't have to do this - they have gills that are able
to pull oxygen out of the water.  But dolphins have lungs that they must
fill with air (just like we do).  So, since they also live in the ocean,
they breath by taking large breaths and holding their breath until they
return to the surface.  They can hold their breath for long periods of
time, as long as two hours for the bottlenosed dolphin, because their
bodies are very finely adapted to efficiently exchange oxygen from the air
in their lungs.    So, the steps in breathing are basically just like ours:
 at the surface of the water, the dolphin takes in air so that their lungs
are completely full, they then hold their breath and descend underwater,
while the sacks in their lungs are exchanging the oxygen from the air into
their blood stream, they return to the surface after their dive, and once
they break the surface, they let out the air with a 'blow', and take in
other huge breath.  Unlike us, dolphins are called 'voluntary breathers'.
This means that they must consciously control every breath they take.  Pay
attention to your breathing sometime, you'll notice your intakes and your
exhalations, but after a while you'll realize that you've totally forgotten
about it, and your body just took over.  Dolphins can't do this, or they
would drown.

Eating:  Common dolpins eat fish and small squid.  How do they do this?
Well, dolphins mostly feed on schooling prey because a large school is much
easier to find than a single fish.   Finding this school is also easier
when searching in a group, so dolphins travel in pods and together search
for large schools of their prey.  They use ultrasonic clicks called
'echolocation' to find the schools.  The whole pod scans huge areas of
ocean as they travel.  Once they find a school, they eat until they are
either exhausted or their prey is gone (either eaten or dispersed away).
The dolphins I work with can eat as much as 25lbs of fish a day, maybe even
more.  Common dolphins are bit smaller than my dolphins, so they may eat a
little less than that.   

Giving birth:  All dolphins give birth in the ocean, near the surface.  The
calf comes out tail first, so that the last part that emerges into the
water is their head.  Once born they must immediately swim to the surface
of the water, to take their first breath.  They may either do this on their
own, or they may be helped by their mother or another animal.  Most
dolphins give birth to only one baby at a time.  Rarely, a dolphin has been
observed to give birth to two babies (twins) but one of the babies almost
always dies because their mothers are just not able to take care of both.
Newborn common dolphins are about 1.5 feet long.  How many babies does one
female have in her lifetime?  This is a good question, to which we can only
estimate the answer since we just don't know for sure.  Females have babies
every 2 to 3 years, and they are sexually mature for about 25-30 years.
So, if they were healthy and breeding their whole life, I guess they could
have about 10-15 babies in that time.  

Good luck on your project!

Jen Philips  

Jennifer D. Philips

Marine Mammal Research Program
HIMB, University of Hawaii at Manoa
PO Box 1106			
Kailua, HI  96734
voice:  (808) 247-5063
fax: (808) 247-5831