Tuesday, February 8, 2011

Naked Mole-Rats – Year in Review

In addition to tracking 2010 statistics from our butterfly shipments, we in Life Sciences love to pore over the data from our other animal exhibits -- particularly the naked mole-rat colony.

Each year, we put together a review of all of our observations and records. Reflecting on this information gives us a better idea of overall colony health, and allows us to identify any long-term trends or changes.

Here are the major highlights:

Naked Mole-Rat Colony Population:
January 2010 = 27
January 2011 = 41

Deaths by year (adults and independent juveniles):
2008 = 9
2009 = 2
2010 = 1

Total recorded pregnancies: 8
Total recorded births: 8
Total pups born: 152
Average litter size: 19
Total successful litters: 1
Total surviving offspring: 13
Pup survival rate: 9%
Deaths of pregnant females: 0
Live parous females: 2

Weight changes from Jan 2010 to Jan 2011:
Average weight difference: +13.8 grams
Average weight difference among adults 2 years and older (pre-2009): -2.7 grams
Average weight difference among juveniles born in 2009: +18.5 grams
Average Jan 2011 weight of pups born in 2010: 31.7 grams

2010 weight changes by size – groups are divided based on their size in Jan 2010

In the above graph, the individuals within the 5-25 gram category are actually from two separate age groups. Most of them are the juveniles that were born in 2009 and they have showed a marked weight increase throughout the year. The average weight for this size group would likely be even steeper if it didn’t also include three individuals from the age group born in 2006 (including “Toothless Wonder”. We refer to them as the Runt Group). These three have not gained weight in over four years and we don’t expect them to grow much larger. All of the juveniles born in 2009 and 2010 have surpassed the Runt Group in size and weight.

Things To Note:
We continue to see the overall body mass of the colony increase. The success of Galinda’s March litter was another major milestone on the path to a healthy and sustainable colony. Although we were pretty optimistic about Galinda’s litter, we were still amazed that 13 pups survived from one litter. This is the largest recorded survival rate of any litter at Pacific Science Center.

Galinda and Elphaba continue to coexist rather peacefully and both are still reproducing. Galinda still appears to be the stronger female, but neither seems to be bothered by the existence of each other’s pups. In fact, we have even observed Galinda attempting to nurse some of Elphaba’s pups. We aren’t sure that she was successful though. If you look at the literature on naked mole-rats, this behavior is still unheard of in other colonies. We wonder if perhaps these two are closely related.

One interesting story from 2010 was the emergence of the disperser morph. A few months after we successfully secured the enclosure from escape, he lost most of the weight that he had gained in preparation to his escapes. Now he weighs about 61 grams, down from 81 grams. He still looks healthy and behaves normally, but the dispersing behavior has totally disappeared. Why did he change so suddenly? He may have assumed a new role in the colony, as a breeder male, taking on the much thinner physique that is typical of other breeder males. Or perhaps he just gave up on escaping and decided to stop eating so much.

After reviewing the statistics and stories from the past year, we continue to have an optimistic outlook for 2011. Please check back with us here or visit us at Pacific Science Center to find out what’s new with the naked mole-rats.


  1. Hello,

    I was at my local zoo today and noticed what seemed as a NMR eating a newborn. Does this happen?

    I noticed there were 3 lifeless newborn in the "pantry" and two with the female and other NMRs.

    One was quite active when approached by another NMR who seemed to want to "grab" the infant with its mouth. The infant opened its mouth and the larger one backed away and released the infant.

    The other was, what seemed to be, eaten by the female. When the female released the infant it did not have a lower body.

    Today's visit has certainly peaked my interest in these fascinating creatures!

    Thanks for such an informative blog on the NMR and their two queens. I will be tuning in to see what happens :-)


  2. Hello anonymous. The behavior you describe is something we've read about often in naked mole-rat publications. When I started working at Pacific Science Center, I was cautioned that this might happen. Our protocol stated that if a pup were found dead in the colony, it should be left for 24 hours. The concern was if the colony had a sense that there was a dead pup but couldn't find it, they might attack a different pup to "Make up the difference". However our colony shows fewer aggressive behaviors than most, and does not seem inclined to attack or canibalize young.

    Often when I think a pup is being eaten, I discover that really it's a yam!

  3. Sarah,
    Interesting! Thanks so much for taking the time to answer my question :-)