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Nest 20 predated

Toa Kyle | Nov 23, 2006


We’ve lost nest 20 to predation.  I mentioned before that when a chick is over 300g its predation risk is lowered.  Nest 20 has proved to be an exception.  One of our crew went to check on this nest the other morning to find a distressed nesting pair and numerous vultures circling above the nest.  When he inspected the nest cavity, only portions of the nestling’s head and feet remained.  This chick had to be well over 400g when it was predated.  I back to wondering if a Great-horned Owl is responsible. 

Whenever we lose a BTM nest I’m left wondering if I could have done more to prevent it from happening.  This particular nest had an open crown.  By installing light weight roofing, we could have better protected the nestling by shielding it from predators that fly overhead and limiting access to the nest cavity itself.  We discussed doing this when we first discovered the nest but had misgivings about attempting to do so due to the flimsy nature of the upper portion of the nest.  In the end we decided not to take the risk of the nest cavity collapsing due to the extra weight added by roofing.  In retrospect I wish we’d experimented with something.  Losing a BTM nest always stings a bit.  We put up a nest box in this island with the hope that the pair will take to it the next breeding season.  They’d already invested two months in this year’s nest (one month incubating and one month caring for a nestling) so it’s unlikely they’ll nest again this season.

We also put up a box in the island where we’d seen t the wounded female a week ago.  She was around with her mate and showed no visible signs of injury.  The pair has shown no interest in the snag they were excavating in October.  I’d be surprised if they did up nesting after seeing the female in such a bad state recently.

Something interesting happened while I was up in the ropes installing the nest box.  There was a pair of BGMs perched around 30m me, chatting with other parrots in the forest island.  In a flash a Southern Caracara Polyborus plancus dove in from nowhere, taking a swipe at the BGMs. 

The attack was unsuccessful but totally surprised me.  On one hand it’s rare to actually witness a predation attempt and on the other, I didn’t know that Southern Caracaras were potential predators of adult macaws.  Normally I’d seen this species feeding on motacu fruits or hanging out with vultures at cow carcasses.  That some individual caracaras go after large macaws may explain some of the macaw remains we’ve found throughout the course of the project.  This species is abundant where BTMs are found.  I suspect that preying on macaws is not an inherent trait for caracaras rather that some individuals do it opportunistically.  We may have to look at predator control (ok, a euphemism for shooting predators) on a case by case basis.  Both Southern Caracaras and Great-horned Owls have large distributions and are not threatened where BTMs are found.  We simply can’t allow these species to feed on the few remaining BTMs in the wild. 

Having lost nest 20, I shifted our attention to the southern BTMs.  There’s an estimated 25 BTMs one hour south of Trinidad.  For unknown reasons this subpopulation tends to breed later than the northern birds, usually around the same time as BGMs.  I’d like to work with at least one more nest this season so the south may be my best bet.

One regretable trend happening in the south right now involves a nest box program for BTMs initiated by Armonia, another NGO working with the species.  Last year the put up 20 boxes in the area, the majority of which were occupied by BGMs (75% of all boxes).  Clearly something had to be done with the entrances to these boxes to exclude BGMs but allow smaller BTMs to enter.  Alas, no changes were made and of the four boxes I saw at a ranch we work at, all were occupied by BGMs, two of which are incubating.  The last thing we need in this area is more BGMs chicks fledging.  BGMs compete with BTMs for nest sites and resources.  Due to their larger size they usually win most confrontations.  Being superior in numbers doesn’t hurt their overall success either.  In past years at this particular ranch I could regularly see a BTM pair around the house.  Not so this season.  Unfortunately three of the nest boxes occupied by BGMs are in close vicinity of the house.  On several occasions I’ve seen these pairs aggressively defend the area around their nest box from other macaw pairs that fly too close.  Presumably the BTM pair that formerly inhabited this area received the same treatment.  By bringing this up I don’t mean to criticize Armonia’s actions rather point out again the need to learn from the mistakes of past field seasons and fix them for the future.