When is it too dark?

To shoot or not to shoot; the light was decent right up to the point that we found this fledgling Great Horned Owl. Then the clouds rolled in. I was shooting with my wife who opted for a very low shutter speed with some support from a monopod. I was very surprised at how well her 1/30th of a second shots with the new Tamron 150-600mm lens turned out. I went a different route and set my camera to auto iso and stayed with a higher shutter speed. In this case the iso jumped up to 10,000 and 5000 in the picture below. With lots of post processing we got a few shots that will never hang in a gallery but provide some nice memories of our owl hunting trip.