Most people who do bird work get into a rigidly defined schedule. More often than not, it involves waking up early– often hours before sunrise– and going to bed early to accommodate for our early-bird hours. Seabird work here on the Refuge is a bit nicer, with our day officially starting at a relaxing 7:00 am. For the past few weeks, however, the Ship Island crew has had to turn our schedule topsy-turvy, thanks to a dastardly nocturnal visitor: a great-horned owl.
Kelby first spotted the owl on an inauspicious morning in late June. We tossed up a first round of traps that very day, but the owl didn’t return for almost two weeks! When it did return, we knew it had discovered the tern colony from the number of bodies left behind. Over the next few weeks, we gradually increased nighttime monitoring, starting with midnight trap checks and escalating until we had somebody present in a blind during every single hour of the night.
Thankfully, our efforts paid off. At 12:17 am on 7/21, as I was tucking myself into bed after the 9-12 blind stint, I received a phone call from Kelby: we captured the owl!
Our adult and fledgeling terns face predation from various birds of prey, and not all of them are equally problematic. We have near-daily predation events from nearby nesting peregrine falcons, which accounts for dozens of casualties over the course of the season. This doesn’t seem to disturb the terns outside of the five minutes or so that the falcon is present, however. The same goes for merlin, northern harrier, and even the occasional Cooper’s hawk that finds its way out to Ship.
Terns and other seabirds have evolved a colonial defense against aerial predation, accomplished by banding together to evade capture in spectacular dread flights or by chasing off the predator altogether with brutal dive-bombing and excrement-shooting tactics. Nocturnal predation, however, is a different game altogether; the adult terns panic when they are threatened by a predator they cannot see, and will simply leave the colony for the night if they feel unsafe. If an owl is visiting for consecutive nights, fattening up on a steady diet of tern chicks and fledgelings, the adults will eventually decide not to return the next morning at all. That leaves the entire year’s worth of chicks to starve and fall victim to plundering by gulls.
It turns out that this particular owl has been visiting more than just Ship Island for its nighttime escapades. A brief trip to Trumpet Island revealed at least five gulls recently killed, and we have heard nighttime disturbances from the birds nesting on nearby East and West Barge Islands at well. Even though we will only be able to see the positive effects of apprehending the owl here on Ship, we can rest easy knowing that the threat to the other nearby seabird colonies has been mitigated.
What happens next? Our big “friend” spent the night here on Ship but was picked up promptly the next morning. It will spend the rest of the week in a fancy flight cage with a local wildlife rehabilitator until it’s time to drive far, far inland. The owl will be released at a lush forest camp teeming with plenty of non-seabird prey, where he can live out his days hunting responsibly.
That’s all for now. We’ll have one last update on island news within the week. Closing is on 7/26 (!), but work will continue right until the end.
Meredith, Ship I.
Bonus bird fact: the great-horned owl’s closest North American relative is actually the striking snowy owl. While they may seem quite different at first glance, they share many morphological and ecological similarities. This even includes those striking “horns”; if you see a snowy in the right wind, you might catch a glance of its miniature ear tufts.