Monday, March 31, 2014

Cub demography

Cub pile at South's den.

A major part of a research assistant’s job is keeping up the clan demography. This means keeping track of rank changes and new immigrant males on occasion but mostly means collecting demography information for all the new cubs. Most of the cubs are born around between October and February, but they don't really start to come out of the den until they're one to two months old and they don't get really bold and playful (i. e. start playing underneath the car) until about 3 months. Now that it's March just about every mom has brought her cubs to the communal den of each territory, so we have our hands full! The information we need for each cub includes: who is the mom, if the cub has a sibling, is it subordinate or dominant, what is the cub's sex, and how old is the cub? Additionally, as soon as a cub gets spots we need to get good left and right side photos so we can learn how to ID the cub.

Sport and Citrus investigating the car.

It’s a great excuse to sit at the den and watch cubs play for hours but it can also be very stressful when there are 8 little cubs just starting to get their spots running around and interacting with other hyenas, especially when you have no idea who their moms are. In order to confirm a cub’s mom we have to see it nurse. Sometimes we see this right away and sometimes we have to give a cub a nickname that we’ll use for several weeks until we see it nurse.

Serena's cub board. IRL is short for inter-litter rank, DFS is short for date first seen, and DOB is short for date of birth. 

Yesterday we redid the cub board and removed all the older cubs that were born last year and are no longer living at the communal den. We use this board to keep track of each cub’s information as we collect it. “Citrus” (at the bottom of HZ) is the nickname of the only unIDed cub at Happy Zebra. Since all the mom’s have a specific theme for their cub’s names we can’t give Citrus a real name until we know who his mom is.

This is Higgs-Boson (mom's lineage is subatomic particles) when he was about 4-5 weeks old. At this age they get pale rings around their eyes.

This is Death Star (mom's lineage is space ships) when she was about 7 weeks old. 

Giving a cub a birth date is usually the hardest part. When cubs are between 3 and 9 weeks old aging is usually straightforward based on the amount of white on their face. Between 4 and 5 weeks cubs get pale rings around their eyes which eventually around 5 to 6 weeks turn into white eyebrows. Gradually the white will spread back over their entire face so that at around 11 and 12 weeks their entire head is fairly pale. By 3 months old their black is well on the way out and you can see shoulder spots but the variation at this age starts to broaden.

This is Clever Girl and Shooter (mom's lineage is Jurassic Park quotes) when they were about 3 months old. Notice how the darker fur is just starting to leave their shoulders.

Once a cub starts to get spots the next important thing to do is print photos of it’s spot pattern and learn how to ID her! For each clan we have a book with right and left side photos of every hyena.

Happy Zebra's clan book with ID photos for every hyena. On the front page is the social hierarchy. Offspring are tabbed once underneath their mother.

Right and left spot photos for some of Happy Zebra clan's cubs.

Eleanor nursing her two cubs Hey Jude (in the subordinate position) and Michelle (in the preferred position).

If a mom has two cubs, we also try to identify the dominant and subordinate cub. There are two ways we can do this, the most reliable way is by observing an aggressive interaction between the two cubs and noting which cub was the aggressor and which cub put its ears back and acted submissive. We can also get an idea by which cub is nursing in the preferred position. A mother hyena has only two nipples between her two back legs and all cubs to prefer to nurse parallel to mom, tucked up against her belly. If this position is occupied by the dominant cub the subordinate will nurse between his moms hind legs. This position is less desired because the cub doesn’t get mom’s body heat and can’t be groomed by mom when she’s nursing.

Some cubs, especially smaller ones, often nurse parallel but the cub closer to mom still occupies the "preferred" position. This is Sherman with Astronaut and Rocket Scientist (her lineage is professions).

Cubs also sometimes nurse while their mother is still standing up. We call this nursing "on hoof". This is Teddy Bear nursing from Saur with Gummy Bear off to the right. Saur's lineage is types of bears. 

The next thing we do for a cub, once we know who it is and we can reliably identify it, is try and sex it. Since female hyenas have a pseudo-penis, which we call a phallus, sexing can be difficult. However there are some distinctive morphological differences between male and female phalluses that is detectable even in the cubs. Male phalluses are very pointy, almost spade shaped with a very defined constriction before the head. Female phalluses are either round or blunt at the end and have some to no constriction. These differences can only be seen reliably when the phallus is erect.

This is Blue Band, a female hyena cub.

This is her brother Kachumbari. (Their mom is Clovis, whose lineage is condiments. Blue Band and Kachumbari are both kenyan condiments).

One may think it would be rare to see a hyena cub with an erection but for hyenas the phallus is a tool for social communication. When two hyenas greet each other they typically become erect and will sniff each other’s phalluses. Since all the hyenas love to get to know the new cubs there's usually a lot of social interaction going on at the den and it's not too hard to spot a cub’s phallus. To be on the safe side we always sex a cub three independent times before we can be sure of its sex. On our cub board the black gender symbols indicate the 1st, 2nd, and 3rd sighting. The colored gender symbols indicate a 100% confirmed sex. As you can see we don’t always get it right the first time!

Eremet play-biting Falkor's hind leg (the cub on its back) while Spyro goes for Falkor's ear. (Eremet's cubs are named after dragons).

This is my favorite part of the job because between IDing, aging, and sexing cubs we just get to watch them nurse and play romp!

North cubs debating about whether nor not to go underneath the car.

Sherman's cubs chewing on her radio collar.

UPDATE: Sherman and Hooker both now have really little cubs and don't seem so into fighting Waffles for North's matriarchy. Hence, Waffles is still holding the throne (which some major help from her daughter LogC).


Zoe Johnson-Ulrich said...

Love this post! So many cubs! But the picture captions seem to be running off and disappearing.

Julia said...

That board is a thing of beauty :)

dee said...

Another really fine post. AND I can update info from the board! Thanks!

Michigan State University | College of Natural Science