Dicromantispa interrupta

Dicromantispa interrupta

Tuesday, February 24, 2009

Third Round of Caracara Surveys Completed

Today ended a round of field surveys for crested caracara (Polyborus plancus) nests. The team has found all the “easy” nests along the project route, so the remaining work results in fewer caracara observations. Other wildlife keeps things interesting though. Yesterday, at a semi-developed location, I spotted a river otter (Lutra canadensis) in the morning and a bobcat (Lynx rufus) in the afternoon. I get to see otters only two or three times a year, and that may have been only the 6th or 7th bobcat of my life. A gratifying coincidence and a good day.

The caracaras I was supposed to observe leaving their nest before sunup this morning either outsmarted me or have abandoned the nest that is thought to be there. Better luck next time. Sometimes the magic works, and sometimes...

Appx 10 percent of pairs breed twice in a given year, I suspect due to environmental conditions. Most of the pairs we have found seem to be gearing up for a second breeding. As I survey the pastures and marshes that the caracaras forage in, I see zero prey capture success in the uplands whereas predation success seems to be high in wet marshes. Unfortunately, the marsh wetlands around here have nearly all dried up in the spring drought, so what will they feed a second brood?

The books say that caracaras eat a lot of things, and they do (doesn't most?), but let's take a closer look. I have been surveying for caracaras and their nests now for about a month. I see no real prey in the pastures; the winter grass is too short for rodents or snakes to hide in, and the only rabbit seen was in a Brazilian pepperbush (Schinus terebinthifolius) thicket. I'd like to see a caracara catch a rabbit in there!

Another team member today watched as a caracara ran down and caught a young cottontail rabbit (Sylvilagus floridanus). I bet that was an amazing sight! Now I know what those long legs are for. I had guessed they were useful in tall grass, and I suppose they are, but thinking about it further now I realize long legs are usually more for running than stilting. Rabbits are fast, even young 'uns.

So then, what are the caracaras eating now during nesting season? I observe they spend more time over marshes that still have water in them. These wet marshes still have frogs, fish and snakes in them, and I believe they are pretty much the main larder right now. But the marshes are drying up. A dried marsh is even barer than a short-grass pasture, so again prey is rare or absent. What will they eat in the coming month or two? Will it rain in time for the second hatching, or is the permanently inundated marshland area sufficient for only for 10 percent of them?

They also eat carrion along the highway. We have noticed that caracaras make a “highway run” first thing in the morning, right at daybreak when roadkill can first be seen by this diurnal species. Perhaps as the mammalian young of last year are run off by their moms who are getting ready for this year's litters, their highway naivete will translate into increased roadkill as springtime comes into full flower.

Wednesday this week I spotted a burrowing owl (Athene cunicularia ) in a pasture. I had seen burrowing owls only a few times before today, and had never before seen their nest burrows. The owl would radiate out from a central location over the pasture. It appeared to be hunting when it flew off short distances, and sometimes disappeared into a burrow or a depression (I couldn't tell which) after a short forage. Presumably, it was returning to the burrow nest after each successful hunt to feed its young or mate. I could not look for a burrow on Wednesday, so I returned today to do so.

Walking a transect I set up on Wednesday in anticipation of the search, I quickly found two burrows. They are about 12 ft apart and 5 – 6 inches in diameter. There were a few small feathers in the runway of one burrow. Perhaps a dozen false starts were scattered around near the two burrows. A false start is a burrow abandoned before it is completed. These could be confused with armadillo diggings, which are funnel-shaped, whereas an owl's false start has cylindrical sides and a hemispheric terminus.

The nine-banded armadillo (Dasypus novemcinctus) digs for small to tiny animals to eat, like ants and earthworms. When it smells a single prey item like a beetle grub, it excavates the least amount of dirt necessary to reach it, and a funnel shaped hole is perfect. We like the fact that the armadillo eats insect pests, but the 'diller has a devious side, too. One of its detriments is its propensity for taking over other animals burrows, including the burrows of the imperiled gopher tortoise (Gopherus polyphemus). Looking at an armadillo burrow near the owl burrows, I wonder if the nine-banded also takes over owl burrows?

I have read that Florida's burrowing owls usurp burrows of raccoons, snakes and gopher tortoises. I don't believe that for a picosecond. The raccoon (Procyon lotor) does not dig burrows in Florida, Florida snake burrows collapse right behind our sand-swimming serpents, and tortoises can fend off any mere tweety bird. Ok, ok, we're talking about a hooty bird, but it's still small relative to the tortoise. No, the owl burrows I saw today were dug by owls.

1 comment:

  1. Hi! I just found your blog. I did a presence absence survey on Caracara here in Brevard County.. Have you seen my website? http://caracara.fieldguideflorida.com?
    Do you do surveys for your own use or for someone else?