Dicromantispa interrupta

Dicromantispa interrupta

Saturday, February 6, 2010

Caracara Nest and Nest Tree

When I first learned last year that I was going to be looking for nests of the crested caracara in South Florida, I reviewed information available on the internet about their nests and nest trees. I wanted to know what I was supposed to be looking for in terms of what species of trees, how high off the ground, construction materials, microhabitat, and anything else that might be pertinent. I learned that caracaras make their nests in cabbage palms 97% of the time in Florida (saguaro cactus in Arizona), but could find no real verbiage on the flavor of the palm or its nest. This post seeks to partially rectify that situation. I have seen a couple of dozen caracara nests by now, not very many by any means, but there are consistencies in what I am seeing that might benefit others. At any rate, the information in this post is more than I could easily find on the internet elsewhere.

Most nest palms are within small groups of one to eight palms and are rarely at the edges of or within large hammocks. It is believed this enables caracaras to have almost unrestricted vision all around the nest tree so that they may better keep a vigil for predators and prey. The typical nest tree is close to several good perches, preferably snags (dead trees), but they will sit in the canopies of living trees if acceptable snags are in short supply. The nest tree is often close to a freshwater pond or marsh so that adults do not have to travel far to get food for mates and young. This photo shows a typical nest site, with the nest being in one of three adjacent palms, two more solo palms in the near distance, and a nearby snag and pine with commanding views. The closest palm contains the nest.

The canopy of the tree will often have a single "landing gap" facing a clear flyway that the birds use to enter and exit the nest canopy. Interestingly, the palm frond on which it perches does not suddenly shake when an adult launches itself from the palm canopy, Even when I watched the nest tree intently, a caracara will seem to suddenly appear out of thin air from behind the tree rather than leave a shaking limb in its wake. This may be a way to avoid giving away its nest to a predator.

The nest tree will not have petiole “boots” still in place from the ground up, presumably so that snakes and other predators cannot easily ascend and attack eggs and nestlings. The tree will have one to several lianas (woody vines), but they will not bush out along the trunk and create a ladder for interlopers. The net effect is a smooth and clean trunk that frustrates nest predators .The tree will be old enough that it has several year’s worth of dried inflorescences still firmly attached and emerging beyond the canopy. Lianas climb the inflorescences and “bush out,” thus creating a “rat’s nest” of tangled vegetation that is large and dense enough that a medium-sized bird nest cannot be easily seen from the ground. Caracaras will tamp down the tangle to make it flat on top and will then augment the platform with dried vines and cabbage palm “socks.”

What are cabbage palm boots and socks? Look at the picture below of a relatively young cabbage palm, noticing on the ground the three Y-shaped thingies and the mass of light brown fibrous material. The Y-shaped boot is the basal part of the palm frond petiole (leaf “stem”) that attaches the palm leaf to the trunk. A few months after a cabbage palm leaf dies it will break off a short distance away from the trunk leaving the boot firmly attached to the tree. When looking at a bunch of cabbage palms, you will often notice that some palms retain their boots and others do not. Evidently, the palms must reach some threshold height or age, or something, before the boots drop off. The fibrous material is produced along the margins of the boots, but by the time the boot falls off the tree, the fibrous material has long since rotted away. For the caracara to use these fibers, it must pick at them when they are alive and tough, near the top of the tree.

Florida Crackers have been calling Y-shaped frond bases “boots” for a long time. I may have independently invented the use of the word “socks” to apply to the basal fibers (socks go with boots, right?), but it’s such an obvious connection that I bet it’s been made before.

In addition to the vines and flower stalks, caracaras weave slender, supple pieces of vegetation and plastic into the nest. The vegetation used seems to be primarily greenbriar (Smilax spp.) stems, but only the very thin, wiry ones with tiny spines. They will also use grasses and stems from other vine species. One nest examined contained black plastic strapping and orange plastic packing twine, and another nest had a piece of red plastic surveyors flagging waving in the wind. In all the cases I have seen, however, nest materials were slender and supple rather than stout and stiff.

Especially interesting is that the adults weave a tightly packed pad of palm sock material appx 10 to 12 inches in diameter and 3 to 5 inches thick into the top-center of the nest. This not only provides a soft, insulating substrate for family, but also is gentler on the bare bottoms of incubating adults and  nestlings. This pic below shows a downed nest that gives you some idea of the overall size, 2.5 – 3 feet in diameter, plus the sock pad (broken up).

As the palm grows upward and its lower fronds die and fall off, attached lower portions of large nests will break away and fall to the ground. If a nest is used every year for several years, it will look like a column of debris extending vertically through the canopy fronds. Sometimes the column will be 4 - 4 feet in height, but most nests I have seen are not so fully-developed. I imagine that as the nest ages and settles, mold and parasites might make it uninhabitable. This is a likely explanation of why they use a nest for only a year or two, and move around among several nests over the years.

The tree may have a very few bird droppings under it because they release most of their feces elsewhere. Favored snags and the ground underneath are sometimes spattered with droppings and may the have remains of food items scattered about. Armored catfish, cattle egret feathers, and miscellaneous bones are frequently found. Oddly, this caracara eggshell was found under an active nest. Ordinarily an adult would remove the egg from the area of the nest.

The caracara is careful in other ways to keep the secret of the nest location. The male and female do not enter the nest at the same time, so predators don’t get a quick second look. They tend to enter the nest fast and from a cryptic route. They will rarely enter a nest if they know someone is watching. At day’s end, they have a neat trick or two to fool you. If both are out of the nest but close by appx an hour before sunset and well before nocturnal predators some out to hunt, the male will suddenly leap off his perch and fly in plain sight only a few dozens of feet from you and tear then outta there fast! You will get excited and jump up and run to follow it with binoculars to see where it goes, but it quickly flies behind a tree line and is lost from view. You look back to the perch to see what the female is doing, but she is gone, vanished. You realize you’ve been had. She snuck into the nest while the male decoyed you away! Now the male needs to get into the nest without being seen. He returns, and if you are still there and he sees you, he has another trick up his sleeve. He waits until about 10 to 15 minutes after official sunset, when there is just enough light to fly by, and then he suddenly launches and flies off again. Again, you jump up and run to where you can get a clearer view of his flight path, but he rounds a corner and is gone. You don’t realize it until it is too late that he is flying a circuitous route to land on the other side of the nest tree canopy.

How do I, the professional wildlifer overcome these diabolical stratagems? Stay tuned, because evolution has prepared me, too…

1 comment:

  1. Buford,
    I have been similarly fascinated with this magnificent bird of prey. I am by no means a birder, but find all hawks, falcons and kites a true joy to watch. I have a retirement home in Bandera, Tx. which is part of an old ranch. The property across from me is apparently home to a nesting pair and a wounded chick which cannot fly. I have been observing them for about 4-5 months now and they appear to be quite territorial even to the point of the pair chasing a redtailed hawk out of their territory. That was a joy to see the three of them soaring through the air as the caracara sternly drove the hawk from the area. Even though the chick is now mature, the parents still share a catch with it and bring it for the chick to eat on the ground. I expected the mature birds to migrate for the winter, but they appear to well suited to staying where they are. I have not been able to spot a nest even though there are only oaks and cedars in the area. The chick has also been spotted walking the sides of the road looking for whatever it can find. I've been trying to get closer to what serves as the primary food source and have come to the conclusion that there isn't one. They appear to eat anything that can't get away. A recent kill was a fully grown jack rabbit. I could see one of the birds in the tall grass apparently feeding. Upon looking at the area after the bird had left, I found nothing fut the upper abdomen and front legs remaining. The chest had been plucked clean and skinned. there were severla lacerations in the flesh as though it had been sliced surgically. I checked the site about mid-morning the next day and the carcass was completely gone. This could have been the work of other predators, of course. A few days later, I observed another feeding session, this time definitely by the chick, since in getting a closer look I scared him off. This kill site consisted of only about a 4" section of spine completely devoid of flesh of any kind, just bright red blood covering the remains.