Record Mammal Big Day

Three mammal big days run in central California in the last few years have yielded significantly higher totals than the few other attempts in the U.S. of which I know. These included 31 and 30 native species in August of 2014 and 2013, respectively, from Peter Pyle, Floyd Hayes, and Sarah Allen, joined in 2014 by Gary Fellers and Pat Kleeman (link). They covered Point Reyes National Seashore from midnight to dawn, spent much of the daylight on a pelagic trip to the Farallon Islands, and covered other Marin Co. locations in the evening. My wife Eileen and I tallied 27 natives in August 2014 (link). We covered Santa Cruz Co. from midnight to early morning, took a half-day whale-watching trip on Monterey Bay, briefly sampled the west edge of the Great Valley, and spent the last 5.5 hours of the 24-hour period at Pinnacles National Park.

When I read about the two big days in the North Bay area, I was very impressed by their midnight to dawn segment, which was well scouted and delivered outstanding variety. Their Farallons pelagic leg produced just under one new species per hour, a fair result, but their evening route had a relatively low yield. In comparison, our midnight to early morning segment was decent but nothing special; and our daytime whale-watching and Great Valley foray yielded under 0.5 species per hour, which was dismal. But the evening at Pinnacles was excellent, adding 2 species per hour, a very high yield for the last quarter of a big day. So I wondered if the first 2/3 of their route could be combined with our evening segment to yield a higher total than likely on either route alone. This involved an extra drive of over 2.5 hours with no expected new mammals, but it appeared feasible. So Eileen and I proposed the idea to Peter and Floyd, and it was agreed, leading the four of us to attempt the route on August 9, 2015, the date of Debi Shearwater’s summer Farallons trip (Sarah, Gary, and Pat were unfortunately unable to join us).

The pre-dawn segment at Pt. Reyes was indeed excellent, with 21 species by 5:36, including Aplodontia (heard only) and Badger. We found three species not recorded in this area on either of the two previous big days. Hairy-winged (Long-legged) Myotis was flying over the bridge on the Abbott’s Lagoon Trail; the ID was based on full-spectrum recordings, analyzed nearly in real time on a laptop. Nearby, Floyd conscientiously flipped each of a set of canoes that had flattened the vegetation under them, and the last one produced a tiny dark mammal scurrying away. “Look — a mole!” “No, it’s a shrew!!” “NO, IT’S A SHREW-MOLE!!!”

The final surprise was seen as we peeked over the bank above White House Pool, when an adorable Western Harvest Mouse emerged from the sedges at the water’s edge, sat in the open just ten feet away for perhaps 15 seconds, and then hopped along the bank, allowing us to follow it briefly. This was a lifer for everyone! But somehow, that morning, we missed Raccoon, a species that seemed to be everywhere on Pt. Reyes during the previous two years.

As Eileen and I did not see a California Vole under one of the canoes, Peter paddled us across an estuary branch to an island opposite his house, and flipped over many pieces of plywood until the situation was rectified. Thanks, Peter! One of the great nemeses of the previous big days, Sonoma Chipmunk, finally deigned to appear in Peter’s yard shortly before the mandatory departure for the boat, instead of just after, as in past years.

The trip to the Farallons was pretty similar to those of the preceding two years — outstanding for pinnipeds (all possible species), but somewhat disappointing for cetaceans (only Harbor Porpoise and Humpback Whale). The birding was unique, with Northern Gannet (only Pacific record), Brown Booby, and Blue-footed Booby all visible on the cliffs in a single binocular field, which also included Tufted Puffin as an outgroup! Thanks to Debi Shearwater for organizing this trip and allowing us to arrive at the last minute.

As our boat passed back under the Golden Gate Bridge, and we got a cell signal again, Eileen’s traffic app indicated that we had our choice of routes with no major traffic delays, giving us perhaps 30 minutes to spare. So we took Route 101 south to look for a staked-out Bottlenose Dolphin at Oyster Point (within San Francisco Bay!), courtesy of Bill Keener, and then headed for Pinnacles. A scouted colony of California Ground Squirrels had the distinction of being our 32nd species, breaking the previous U.S. record.

After setting up the tents, we hiked up to Bear Gulch Reservoir for bats. We had recorded 5 bat species before dawn, and hoped to double that in Pinnacles. We added Western Pipistrelle along the trail, and at the reservoir, Eileen called out the first Western Mastiff (Greater Bonneted) Bat. This is the largest bat in the U.S. and has an echolocation call that is audible to the unaided ear. After recording Dark-nosed (Small-footed) Myotis and Silver-haired Bat, we started back down at 10:30 p.m. Once back inside the woodland canopy we added California and Long-eared Myotis, finishing the day with 11 bat species, of 16 possibilities in the region.

Back at our vehicle around 11:10 p.m., we trolled the few short roads of the park, finally locating Raccoon, which Eileen and I had managed to miss the year before. After seeing Desert Cottontail, we found the 42nd and final species, 8 minutes before midnight: a Heermann’s Kangaroo Rat, in the same general area Eileen and I had seen it in two of the three preceding years. Pinnacles had added 10 species in 5.5 hours, impressive for our having arrived with 32 species! Our total of 42 native species ties what our team believes to be the world record set by Charles Foley in Tanzania (Birding 37:128-130, 2005).

American Birding Association big day rules require that 95% of all species be detected by all team members. This is a sensible rule, though I have always thought it a bit generous for birds (being largely diurnal and vocal). But it is a real challenge on a mammal big day. Between brief glimpses, faint calls, little slip-ups, and exhaustion during batting, only 32 of our 42 species were detected by all, though 37 were detected by at least three of us.

We had rather good fortune most of the day, so I do not think it would be easy to top this list. The key would probably lie in finding a way to see more cetacean species with fewer hours on the water.

Thanks to Floyd for compiling the table below, listing the species in chronological order, with estimated numbers of individuals. An asterisk denotes a species not detected by everyone.

— Brian Keelan

•  Time      Species (individuals)

1.  00:08     Striped Skunk (2)
2.  00:11      Common Gray Fox (4)
3.  00:14     Mule Deer (37)
4.  00:14     Coyote (4)
5.  00:28     Deer Mouse (9)*
6.  00:33     Badger (1)
7.  00:47     Elk (1; heard only)
8.  01:34     Mountain Beaver (Aplodontia) (2; heard at known colony)
9.  01:53     Brush Rabbit (7)
10.  02:30     Long-legged (Hairy-winged) Myotis (2)
11.  02:32     California Vole (2)
12.  02:32     Shrew-mole (1)*
13.  02:33     Brazilian Free-tailed Bat (1; heard only)
14.  03:31     Dusky-footed Woodrat (1; heard only at nest)*
15.  03:46     Bobcat (2)
16.  03:51     Northern River Otter (2; heard only)*
17.  03:58     Western Harvest Mouse (1)
18.  04:30     Pallid Bat (8)
19.  04:30     Yuma Myotis (5)
20.  05:15     Townsend’s Big-eared Bat (20)
21.  05:36     Black-tailed Jackrabbit (11)
22.  06:01     Harbor Seal (220)
23.  06:50     Sonoma Chipmunk (3)
24.  07:24     Western Gray Squirrel (1)
25.  08:13     Harbor Porpoise (10)
26.  08:47     California Sea Lion (2,500)
27.  11:44      Steller Sea Lion (35)
28.  11:59      Northern Fur Seal (800)
29.  12:04      Northern Elephant Seal (6)
30.  14:57      Humpback Whale (1)
31.  16:55      Common Bottlenose Dolphin (1)
32.  17:56      California Ground Squirrel (10)
33.  19:56      Western Pipistrelle (20)
34.  19:56      Merriam’s Chipmunk (1; heard only)*
35.  20:40     Greater Bonneted (Mastiff) Bat (10)
36.  20:58     Dark-nosed Small-footed Myotis (1; heard only)*
37.  21:17      Silver-haired Bat (4; heard only)*
38.  22:49     Long-eared Myotis (1; heard only)*
39.  22:51     Californian Myotis (1; heard only)*
40.  23:26     Northern Raccoon (2)
41.  23:37     Desert Cottontail (1)*
42.  23:52     Heermann’s Kangaroo Rat (1)