Thursday, March 29, 2012

Egg 1 and 2 Metrics

Mme. Owl made the mistake of spending the night out hunting, so I was able to do some basic science on her eggs while her back was turned.

I can't tell the eggs apart, so I can't say which is the first or second one laid. I can say the following: one of the eggs weighs 20.0 ±0.2 grams and measures roughly 36.44 x 31.75 mm, and the other egg weighs 20.6 ±0.2 grams and measures roughly 36.35 x 32.1 mm. (My uncertainty about the measurements is due to the difficulty of being sure that I was measuring the major and minor axes, and wasn't a little off in some direction. A measuring box with sliding sides would eliminate that problem, but I haven't seen such a thing.)

Comparing these numbers to Gehlbach’s (see The Eastern Screech Owl, pg. 92), these eggs are around 2 grams heavier, 1 mm longer on the major axis, and 2 mm on the minor axis.

Larger and heavier than average should be a good sign for the eggs. Exactly why, is a matter I'm debating with myself. Presumably, either slightly larger owlets will hatch-out, or a larger yolk sack will mean greater food reserves for the developing fetuses. I’ll have to consult my raptor rehabber, but any other bird experts are encouraged to weigh in.

Regrettably, routine weighing and measuring won’t be possible, as interesting as those numbers would be (the weight of an egg decreases as the embryo inside develops and uses-up its yolk sack, so charting the changes in weight over time would be interesting, for a start), because Mme. Owl will begin near-continous brooding with the arrival of the third egg. At that point, I'll be leaving the nest alone as much as possible.


  1. Anonymous8:09 PM CDT

    Chris, great start to the new season! In two months I will be joining Fred and Nancy Gehlbach in the Chiricahuas to finish their study of the Whiskered Screech Owl.. .Fred will be publishing a book on their 10 year study. You two really need to meet!

    I will send a postcard from Arizona!

    Karen B.

  2. Karen B.,

    Fred and I met around three years ago at an Audubon presentation he gave in Austin (thanks Sallie). He gave an interesting presentation and we had a few brief, but pleasant, discussions. But that's as far as it went. I expect I just seemed like another groupie with a souped-up nest box; not the sort of person serious scientists would spend much time on.

    At the presentation, and I believe later by email, I offered him my complete archive of images from the nest box, but received no response. (At 4 images per minute, 2 months per year, over something like 10 years, that's a helluva lot of time-lapse nesting behavior data for some flock of grad students to examine, and might be worth a few new papers for someone.) Maybe I should have worn a t-shirt saying something like "I’ve seen more eastern screech owl nesting behavior than anyone in history. (Probably.)" I'm sure that would have made me look suitably serious and scientific. :-)

    Anyway, I still think Fred's a good guy, and his work would still be great even if, for some reason, he wasn't. So, well done, Fred.

    Please tell him if wants my image archive, it's still his for the asking.