NIGHT DRIVING PROTOCOL
Protocol for Big Bend National Park Amphibian Monitoring Field Crew
Nocturnal surveys of paved roads should be conducted after rains to quantify amphibians.
WEATHER
Watch the weather closely in Big Bend National Park and record precipitation events in the weather notebook. Call Rio Grande Village and Castolon store or rangers for more weather information in those areas. The Daily Weather Report provided by radio dispatch lists the amount of daily precipitation in various locations throughout the Park (Panther Junction, Chisos Basin, Rio Grande Village, Castolon, Persimmon Gap, and Lajitas).
When rain has fallen within a 24-hour period in an area crossed by a paved road in the Park, conduct a night drive survey along that section of road.
ROAD SECTIONS
(This one can be split up: Castolon turnoff to Castolon Rt.#15, 22 miles. Castolon to Santa Elena Canyon Rt. #16, 8 miles.)
The locations of the road sections and number of times each road section was conducted in 1998 (listed in parentheses) are shown in the map below.
SURVEY METHODS
Begin surveying at dark, about 30 minutes after sunset. It does not matter which direction the road section is surveyed. If you drive to the end of the road while there is still a bit of light and then work back to Panther Junction, you will end earlier in the night and have more time to sleep!
On the data sheet, record road section (start location and end location), date, beginning air temperature, beginning sky code, beginning wind speed, and observers' names. Throughout the road section, record areas along the road that received rain (as best you can tell) in the "comments or descriptions" column. For example, record "Pavement wet from mile 2.0 - 8.7."
Drive the road stretch at 25 miles per hour with the windows down (radio off). Listen for amphibian chorusing and watch for amphibians on the road. If amphibian chorusing is heard, pull off the road, turn off the vehicle, and record the species, chorus code (CC: 0 = none heard, 1 = no overlapping calls, 2 = some overlapping calls, 3 = full chorus), and estimate the number of individuals calling for chorus codes 1 and 2 on the "Big Bend Night Drive" data sheet. For example, if you hear four Rana berlandieri with overlapping calls, record Species CC(# of individuals) as Rber 2(4). Also, record the mile (to the tenths of a mile), time, compass direction, and estimated distance of the chorus from the road [e.g., Mile 4.6, 22:40, 120 degrees, 50 m].
If amphibians are seen on the road, pull off to the side of the road, stop the vehicle, and catch them. Use the "Big Bend Amphibians Found on Road" data sheet. Again, record the tenth of a mile and time. Record species, sex, snout-vent length, and body mass. Place the individual in a pre-weighed or pre-tared large ziplock bag and weigh it (g) using a 100 g pesola scale (subtract the bag weight) or a portable Ohaus scale. Note on the data sheet whether you used a pesola scale or the Ohaus scale. While the individual is still in the bag, orientate the frog so its ventral side is on a flat surface. Press down on its back to gently flatten the frog and measure snout-vent length in millimeters using calipers or a ruler.
To determine sex:
Rber - Adult males have enlarged thumbs and thumb pads.
Goli - Males have a dark throat patch and/or an enlarged throat pouch.
Scou - Males are smaller than females and coloration on the dorsal side is muted.
Females have colorful worm-like
patterns of green and
black mottling on the back.
Bspe - Males may have a dark throat patch and/or an enlarged throat pouch. Adult
males may have enlarged thumbs or
thumb pads. Frogs
under 20 g cannot be sexed.
Bpun - Males have a dark throat patch and/or an enlarged throat pouch. Adult males
have enlarged thumbs and thumb pads.
Bdeb - Males have a dark throat patch. Females have a yellow or cream throat.
Hare - Male throat is gray, brown, black, or dusky.
If an adult gives a release call (a short croak or peep) while being held, it may be a male. However, we found adults that had all female characteristics but also emitted release calls. Hence, we did not use release calling to determine sex.
If you find dead amphibians on the road, record species and decide whether or not to collect the amphibian for a museum specimen (if not badly squashed) or for contaminant analyses. If collected, write "yes" in the "collected?" column on the data sheet and write in the comments section what the amphibian is collected for. Store in a labeled (location, date, time, species) plastic bag. For amphibians which will be used for museum specimens, place them in the cooler with ice packs and then transfer them to a refrigerator for the night and prepare them the next day (see museum collection section). Amphibians collected for contaminant analyses should be placed in the cooler with ice packs and then transfered to a freezer upon your return to the laboratory.
Record other animals seen (e.g., snakes, coyotes, mountain lions), mile, and time.
At the end of the night driving survey, record air temperature, wind speed, sky code, and time.
EQUIPMENT NEEDED
In 1998, we found interesting distribution patterns of amphibians along the night driving road sections. Below are shown the locations of red-spotted toads, Texas toads, Rio Grande leopard frogs, and couch's spadefoots documented between Panther Junction and Rio Grande Village over the course of five night drive surveys. Larger dots represent greater numbers of individuals recorded at that location. We will be analyzing the distributions of amphibians along the road stretches in relation to various factors such as elevation, soil types, and distance to drainages.
Red-spotted Toad (Bufo punctatus)
Rio Grande Leopard Frog (Rana berlandieri)
Couch's Spadefoot (Scaphiopus couchii)
PRIMENet Amphibian Monitoring Program
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