13 March 2013

We checked our traps at approximately 10:00 am again this morning and we captured eight animals - four recaptures and four new animals. One of the recaptures was a female we originally captured as a juvenile last July. We recapture juveniles as adults very infrequently, so it is an exciting event when it happens. It is much more common to recapture juveniles within a week or two of being first captured. This leads me to one of two alternative hypotheses: (1) juvenile survival rates are low, or (2) juveniles disperse off the refuge. Currently I have no way of discriminating between these two alternatives but I can conclude that the majority of recruitment of mongoose into the refuge population comes from outside the refuge. Therefore, it seems that an effective control mechanism for mongoose on the refuge would be to install a physical barrier. At a time when finances are extremely tight, I don't see this happening. Instead, there is a nuisance wildlife control officer from the US. Department of Agriculture using kill-traps to eliminate mongoose adjacent to the turtle nesting beaches. Mongoose have been documented as sea turtle nest predators. However, the extent of their impact on sea turtle populations is unknown.

Once we establish our trap sites there is a trap at each station at all times. If a trap has a mongoose in it, we replace the trap with a different trap and transport the mongoose back to our field lab for processing. Several hours later we return the mongoose to the capture location. Today we captured a second male mongoose at a trap site that had captured a male several hours earlier. I can think of two possible explanations for this phenomenon. First, I don't believe mongoose are territorial on St. Croix despite the fact that males are 50% larger than females. I derive this hypothesis from 30+ years of trapping and repeatedly capturing different males at the same trap location on successive days. It appears that male mongoose wander about and don't defend a specific territory. They do, however, seem to have certain areas that they confine their movements to. They likely have home ranges that overlap and fluctuate. I need tracking devices attached to them to test this hypothesis. An alternative hypothesis is that male mongoose act like dogs and scent-mark on top of another male mongoose scent mark, in this case the trap location. It is not likely to be the trap that is marked because traps change as animals are captured. Again, tracking data will allow me to differentiate between these two alternatives. Unfortunately, radio-telemetry is not effective in the dense vegetation that they inhabit and at the present time the commercially available GPS-enabled telemetry devices are outside by budget.

After dark we went searching for scorpions on the Refuge and found only one in the leaf litter. We ran into Mike Evans, Refuge Manager on the beach as we went to view the stars. There is little light pollution on the tip of Sandy Point and one can see trillions of stars. It is truly a breathtaking few of the sky. Mike was waiting for the turtle crew, who walk the beach each night during for months looking for nesting sea turtles. The locations of all nests are recorded and the number of eggs laid per nest. The hatchlings will emerge during the summer. This year there have only been three leatherback sea turtle nests - but the nesting season has just started.

Leatherback sea turtle hatchlings emerging from their nest on Sandy Point National Wildlife Refuge.

Image (captured with my iPhone) of a scorpion illuminated by a black-light on Sandy Point National Wildlife Refuge.

An image of the same scorpion under normal light and captured with Nikon D60. Approximate size is 2.5 cm.