Barn Owl Diet (Ed Levin County Park, CA)
We monitored the diet of barn owls at Ed Levin County Park from July through September 2023. Here are the results:
Also, surprisingly, several wild oat (Avena) florets were found inside 6 pellets. Puzzling!
Updated 10/8/2023.
Comments
@brennafarrell , @merav, @beartracker
Very cool! I wonder if their diet will change during the fall (maybe they'll eat some migrating birds)?
@brennafarrell, I think 2 of the 3 owls I've been following have moved away. I'm finding very few feathers (has molting season ended?) and very few pellets.
The barn owl molting season should be ending soon: https://www.barnowltrust.org.uk/barn-owl-facts/signs-barn-owl-occupation/#:~:text=Females%20tend%20to%20moult%20between%20May%20and%20August%2C. Hopefully one sticks around throughout the rest of fall and winter.
very nice, @truthseqr! I hope you'll be able to continue this great project!
@tfrench, @galecyon, I'm in the process of writing a report about the barn owls I've been following at Ed Levin County Park, CA. I'm having difficulty differentiating observations of Western Harvest Mice from North American Deer Mice. Could you please give me some tips on how to tell these apart? Here are all the barn owl prey observations for this project:
https://www.inaturalist.org/projects/barn-owl-prey-scc
Thank you for all your help in identifying the bones in these owl pellets!! It's been a very fun and educational project.
I'm usually only comfortable IDing one from the other if the upper incisor is present. Reithrodontomys has grooved upper incisors, Peromyscus doesn't. Here's a comparison:
Reithrodontomys:
https://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+3333+1721+4984
Peromyscus:
https://animaldiversity.org/collections/contributors/skulls/peromyscus/p._leucopus/86115.ventral/
Otherwise, size is probably the best distinguisher. Peromyscus should be about 20% larger than Reithrodontomys. In absolute terms, the upper toothrow of Peromyscus truei should be 4.2-4.5mm long, P. californicus should be 4-5.1mm, and Reithrodontomys megalotis should be 2.8-3.5mm. Measurements from here: https://academic.oup.com/mspecies
I don't trust myself to get size right from pictures without a lot of effort, so I usually limit myself to specimens with the upper incisors visible
Thanks, @galecyon!! I'll remember to get a frontal view of the incisors from now on. Very helpful tips & photos.
Awesome!
I agree with everything @galecyon said. These are good suggestions. I am disappointed that you were not able to save the pellets you found and refer back to them when questions arose. As an example, it is very difficult to see the grooved upper incisors of a harvest mouse in your photos, but if you still had the material, it would be very easy to go back and look for this feature. Another similar species that I don't think you had is the House Mouse (Mus musculus) In that species, the back side of the upper incisors has a stairstep, compared to the smooth progression to a sharp tip that most rodents have. Also be aware that if you find owl pellets in dryer habitats, pocket mice and kangaroo rats also have grooved upper incisors.
@tfrench, thank you for these additional tips. Unfortunately, I wasn't able to get a permit to collect the owl pellets at this park. The required liability insurance was too expensive (about $240/year + $50 permit fee). So my only option was to dissect the pellets on site and leave the remains in the park. This was less than ideal for many reasons - the biggest obstacle was the wind, which would often blow the tiny bones away before I could photograph them. Another issue was my inability to clean the bones to remove fur and debris. I did the best I could within these limits. All in all, it was an awesome experience and my granddaughter and I learned so much about these beautiful owls, their prey species, and their habitat. Thank you so much for teaching me about bone preparation and ID!
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