June 12, 2011

Battle of the ages: bull snake vs. prairie-chicken hen

I think it is always good to approach science, and life in general, with the attitude that there are things we know, things we think we know, and things we don't know.  This certainly applies to one of my areas of research: the ecology of birds while they are nesting.  I've been studying this general field since 1993. 

'Things we know' about nesting birds would include the fact that most species have nest success rates (at least one chick leaving the nest) in the range of 5-35%.  Probably a lot lower than the general public realizes, but as they say---nature is red in tooth and claw.  Predators have to eat, too.

'Things we think we know' might include general guesses at what is causing nest predation events.  We can look at the remains of nests and egg shells, and makes some educated guesses.  Perhaps an empty nest means that a snake came by and ate all the eggs or chicks.  A nest filled with munched-on egg shells might mean a mammal of some kind.  Stuff like that...we think we know.

'Things we don't know' includes the daily behaviors and adventures of females that are sitting on the nest.  How often do they leave the nest unguarded?  Are they successful at chasing off predators on a fairly regular basis?  What times of day do they leave the nest?  Do females with successful nests have different behaviors than females with unsuccessful nests?  We really have no clue.  Or, at least we didn't until we started putting video cameras on nests.  In the past 10-15 years, tiny video cameras and associated recording devices have given us an insight into these behaviors.  And, you always learn some thing new.

My prairie-chicken research crew is monitoring hens and nests this summer with video cameras.  Josiah Dallman is an undergraduate research associate, and his summer project is to learn about nesting behavior through video.  There are some keen insights that we can gather from the first look-through of the video, with the take-home message that there is a lot more activity around a prairie-chicken nest than we originally thought.  The hen leaves during the cool morning and late afternoon for 15-45 minutes.  Deer come by and investigate.  Hail storms shower the nest with golf balls.  Life on the prairie.

I'll paste two 'predator' videos here for you.  The first is a visit to a nest by a badger. You'll see an initial 'pounce' and the hen flushes.  The badger checks out the camera at one point.  The badger eventually spends most of the footage hidden, at the left of the screen...you'll see grass moving while it eats the eggs from the nest.  The video is shot with infrared light, at night.

The second is the 'battle of the ages' video.  This hen has already lived through the hail storm.  During the 3-4 days before this video was taken, a snake visited the nest more than once (during the day), and she successfully chased it away.  Then, on the fateful night, the bull snake (we'll pretend we know it is the same snake, but it makes sense) comes back and will not be deterred.  Neither will the hen give up her nest.  It is a battle to the death.  In fact, the field crew later found the hen dead about 5 meters from the nest.  The bull snake and hen leave the video area and continue their battle, so we don't know exactly how the hen died.  But, our best guess is that she was so stressed by the events on the video that she expired--we have to be very careful when we handle the birds for tagging (they are all radio-tagged so we can find their nests).  If stress can kill them during banding and tagging, surely stress can kill them during natural events as well?  You can draw your own conclusions...feel free to comment!

So, it is the battle of the ages.  I've never seen a video like this...with such a back-and-forth between a hen and predator.  Most of the time, the hen gives up and lives to lay another nest.

In fact, this battle goes on across the prairies (and forests, and wetlands) every summer, and has been going on for ages.  The choice of nest site.  Predator versus prey.  The protective nature of a parent.  The decision of when to give up and start over.  This is the sacred dance of population dynamics.  Enjoy the clips.






3 comments:

  1. Carol L. Ott SchachtJune 13, 2011 at 10:55 AM

    Wow! What an amazing and wonderful mother in the Battle of the Ages, Larkin! As a mom myself, I know that mothering instinct and it's incredibly powerful! It's tragic she likely lost her life defending her clutch, but now I understand better some of the extraordinary challenges of being a prairie chicken mother. It was such a privilege to help collar 2 of Lars' chickens last year and to know that at least one had laid eggs! Do we know if she hatched any? With such fierce predators, do you know how many chicks are being hatched and how many are reaching adulthood? Fascinating study... Thanks for letting me take a tiny part and for sharing this valiant story!

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  2. wow, battle of the ages is right - that's downright amazing. At the end of the clip the nest still appears intact - did the snake come back for the goodies, or did mom win the battle only to loose the war?

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  3. Drew...the subsequent footage that we have shows the snake coming back. It ate 4 eggs, which is about what they normally take at one sitting. Our crew found the hen about 4-5 m (off-camera in this clip). I think she probably died at about the time this clip ends...more or less.

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