The forgotten island

So whatever happened to Catalina, you may ask? The last you, as a reader, heard was that the birds were double brooding and the migrants were passing through. Not to worry. We did not abandon that island entirely. Luckily one of our field assistants was able and had the desire to stick around and monitor our remaining nests. As it turned out, only two of the double-brood nests were successful and the rest were lost to predators. Sad maybe, but also very useful information for us as we are interested in per capita rates of reproductive output. The end result of the Catalina field season was that the average pair of warblers was able to raise 3 young to the point of fledging. Much better than last year, when we did not document any fledglings on the island!

If you read my previous posts, you may remember that very few nests were lost to predators in the first round of breeding. You may also remember that snakes were implicated as the primary nest predator on Catalina Island. So why the sudden increase in predation later in the season? Well, one possible explanation is that snake activity increased from the month of March to the month of May. Ectotherms like snakes rely on warm temperatures to heat their body and enable forays in search of food. As the breeding season progressed and the days became warmer, it is likely that snakes were moving across the landscape faster and more frequently - and, as a result, encountering more and more warbler nests.

If you amass hours and hours of nest videos, eventually you are bound to catch a predation event in action. Earlier in the season we caught a california kingsnake taking nestlings out of a nest, but the video was from too far a distance to be interesting beyond simple documentation of the event. But I am pleased to report that Dan (the field assistant who remained on Catalina) got some great footage of one of our last nests being discovered and subsequently depredated by a kingsnake. The nestlings were 7 days-old at the time, and as you will see in the video clips below they made quite the meal for the relatively-small snake. Enjoy!

Clip 1: The discovery


Clip 2: The meal