JAMAICAN BOA
Home Range,
Attraction / Avoidance Behaviour
& Habitat Preferences

¹An additional 2 females and 1 male were transmittered but they either died (1 female) or experienced transmitter failure within four months; they are not included here.
²Mean daily movement per fix was calculated by taking the mean of each linear distance between successive fixes divided by the number of days between the two fixes.
³Mean daily movement per move was first calculated by determining the linear distance between successive fixes in which the snake moved and dividing each by the number of days between the two fixes and then determining the mean of these values.
⁴Guango's transmitter failed early but we include her here because she was recaptured alive September 2011 and recruited into a translocation study.
⁴Toop-Toop (it means "Kiss Kiss" in Jamaican) was experimentally translocated in October 2010. We present only her baseline, pre-translocation data in this table.

Overall, there was no significant (p=0.65) difference in average daily movements between males (19.1 m + 3.9 SE) and females (21.4 m + 3.0 SE) nor in whether a boa was closely associated with Windsor Cave (16.2 m + 2.2 SE) or not (21.6 m + 2.8 SE; p=0.37).

Similarly, there was no significant (p=0.82) difference between boas (male & female; cave & non-cave) with regards to the number of consecutive days they remained immobile (females = 7.2 days + 1.2 SE; males = 6.8 days + 1.0 SE).

However, these "average" assessments mask both the large distances traveled by males in the first quarter of the year and also the bi-modal peaks in April-May and November, when males were noticeably more sedentary over consecutive days.

The April-May peak also corresponds to five observations of pairs of boas either coiled in copulation (23 Apr 2009) or < 5m apart in the same tree (20 Apr 2009;15 & 29 Apr 2010; 26 May 2010). See also Attraction-Avoidance Behaviour.

For Jamaican Boas, we determined the size, shape and usage intensity of home ranges (95%) and core areas (50%) using the Adaptive Kernel (AK) method. The best reference bandwidth was identified when the 95% isopleth transitioned from encircling discrete patches to becoming continuous (i.e., the "incremental increase" method recommended by Kie et al. 2010). But note, for two males (Zippy & Bruce), their isopleths never merged to a continuous outline because they did big sprints. Where relevant (e.g., attraction-avoidance behaviour), we describe Bruce's "Pre-sprint River Range".

We present AK-2D (planar surface area) along with Minimum Convex Polygon (MCP) estimates to facilitate comparison to other studies (e.g., Puente-Rolón and Bird-Picó 2004, Wunderle et al. 2004), but given that planar analyses can underestimate the size of home ranges in topographically-variable landscapes, we also present polygon volume (i.e., 3D) estimates derived from a Triangular Irregular Network (TIN) model.   Please email us for full details on methods and analytic techniques.

Click here to see all boa locations on one map or click on any boa's name to view individual maps.

Windsor Great Cave, which is owned by WWF-UK and managed by WRC, supports one of the largest and most species-diverse bat roosts on Jamaica. There are more than 100,000 bats, of 11 different species, which emerge at dusk for their nighttime feeding activity throughout the wider landscape.

Taking advantage of Strangler Fig (Ficus spp) roots growing along the rock face, a boa can hold on by its lower body and dangle vertically in the huge stream of emerging bats. Immature boas strike at everything they detect . . . and miss almost everything. With experience, they learn to hold their strike until a bat actually makes physical contact with them . . . and then, occasional success.

Because the bats emerge every night (unless it's raining) and their flight activity is timed to solar sunset cues, they are an abundant, concentrated, and reliable prey source year-round. It is well worth a boa's effort to stay in close proximity to a bat-occupied cave. Indeed, the highest densities of Chilabothrus boas in the Greater Antilles are recorded at bat caves (Rodríguez-Cabrera et al. 2015 and references therein).

With the spatial co-occurrence of so many snakes, we wondered whether they would continually run (slither...) into each other (i.e., demonstrate some degree of tolerance or attraction) or if they maintained a minimum distance (i.e., avoidance behaviour) in their spatially-overlapping ranges.

To explore the likelihood of boas encountering each other, we first examined the percentage of overlap in their 95% AK home ranges on a monthly basis (static relationships) and then examined the distances they maintained between daily fixes (dynamic interactions).

Despite having spatially-overlapping territories (esp. the Windsor Cave and Martha Brae River trios), Jamaican Boas appeared to avoid each other in their home ranges for most of the year.

Notable exceptions were in April 2010, when we captured Bruce (non-transmittered at the time) and Martha (transmittered) in the same tree; Marv and Scarv (both non-transmittered) in September 2009, resting on the same horizonal snag at the Windsor Cave opening; and Thingy1 and Thingy2 (both non-transmittered) in March 2009, resting in coffee trees.

Although the Windsor Cave boas maintained the closest distances of all trios, they also demonstrated the ability to avoid each other while resting during the daytime. Such behaviour may enable boas to reduce the chances of being detected by potential prey items or by the parents of potential prey items (e.g., adult birds protecting their nesting territory & nestlings, such as we see with these Jamaican Crows).

Although boas used relatively flat areas (i.e., slope < 20⁰) as one would expect from availability, there is a subtlety to note:   in cockpit karst, both bottomlands and conical hilltops are gently sloped (it's always a relief to get to the top!).

But we see that they preferred to stay at lower elevations (except for the boas at the top opening of Windsor Cave [elev. 220m]) and they used "Forest-Mixed Landuse" (i.e, immature forest with old cultivated fruit trees) significantly more than one would have expected. This was the most structurally-complex of the landuse categories. Forested bottomlands are important! We also note that boas signifcantly avoided the most open of agriculture areas, esp. yam farms and sugar cane / pasture.

Elvis was in the building!
(In the photo, he's wedged into a 5-m long, 4 x 10 cm, rolled hollow steel section.)

But as you can see, Elvis' strong love of spending his days in the roof of "his" outbuilding overwhelmed the dataset and made it difficult to visualize the preferences of the other adult boas.

So, we deleted sub-adult Elvis' data . . .

For 187 (176 arboreal and 11 terrestrial) of the 1241 (15%) analyzed locations, boas were either seen amongst large tank bromeliads (Hohenbergia spp.) or the transmitter signal was highly directional to a cluster of bromeliads. These epiphytic plants collect water in the base of their leaves, which in turn attracts many animals to drink or feed on small aquatic invertebrates: bromeliads are to Cockpit Country what watering holes are to predators in the Serengeti.

Micro-site fidelity
With the exception of "Guango", who was tracked for the shortest period of time (~ 4 months), all boas revisited previous location fixes. Females returned to 10% of locations one time, 2% of locations two times, 1% of locations three or four times, and <0.5% of locations 5, 6, or 7 times. Revisitation of sites occurred most often in June and August-November.

Adult males showed similar rates of revisitation, with 15% of locations revisited once, 2% revisited twice, 1% revisited thrice, 2% revisited four times, 1% revisited 5 or 6 times, and < 0.5% revisited 7 times. In contrast to females, they least often revisited sites in September-October and most often revisited sites in December.

Sub-adult male "Elvis" has a different story. The outbuilding was the centre of his universe:   60% of his daytime resting fixes were in the roof of the building. Within the roof, he particularly liked to return to the SW corner of Room #1, which had good connectivity to an adjacent ackee tree (a tree in which he rested on 4 different occasions during the day and visited on 13 different nights, including one night to eat the nestlings of our "yardie" Jamaican Crow pair 😢 ) and the east-facing part of the roof over Room #3, over the door... so visitors should still keep an ear open for him! To keep himself oriented on the eastern edge of his home range, he liked a huge Strangler Fig tree, which he visited 6 times. We have much more to say about Elvis, so stay tuned.

Interestingly, although there was no significant (p = 0.19) interaction by month for females, males were significantly (p = 0.05) more likely to be seen in the month of August.

Rare...or Difficult to Detect?
Another way to appreciate the cryptic and secretive nature of a Jamaican Boa is to understand how long it can take to actually find a new boa. During the full radio-tracking project (December 2008 - November 2012), WRC staff and volunteers spent > 6,768 person-hours radio-tracking and completing habitat assessments. During all those hours, and with our eyes peeled in the hope of catching a new animal, we only found 26 new boas (ie., average of 260 hours to find each one).

Our limited success was not because Jamaican Boas are rare in Windsor; on the contrary, we'd have to say that they are as common as dirt here! But if someone said "do a specific search and capture survey" to find a Jamaican Boa or to estimate the population size and density, our default setting would be "we're going to seriously underestimate the number present if you ask us to do a Rapid Ecological Assessment."

Click here for the complete list of habitat variables assessed.

PHOTO:  Termite (Nasutitermes sp.) nest being used by Jamaican Parakeets (Eupsittula nana) for nesting in Windsor, May 2009.   Jamaican Boas are confirmed predators of parakeets (Koenig et al. 2015). In addition to providing feeding opportunities, termite nests also are used by adult female (probably gravid) boas, possibly for thermoregulation (this study).