Tierra de Oro Laboratory

Physiology and Ecology in the Pinyon-Juniper Savanna

Category: Wildlife

  • Baja California: Annual Island Survey

    The islands in the Gulf of California provide a natural laboratory for the effects of “spatial subsidy,” the movement of resources from a rich environment (the sea) to a more impoverished habitat (the desert islands). In this context, scientists have studied many species on the islands, including Tenebrionid beetles. The abundance and diversity of beetles on the islands of Bahia de los Angeles have been surveyed for at least 30 years, and my good friend and colleague Dr Drew Talley has been leading the studies for most of that time. In recent years, Dr Natalia Rodriguez Revelo, an expert in beetles and dune ecology, has participated in the work with Drew. I have participated in various roles for several of the past 20 field seasons, and was once again privileged to spend time with them and help out on the islands this year.

    Drew and Natalia counting beetles on La Ventana. 6/28/25.

    The procedure is straightforward in principle: on each island, set multiple pitfall traps (plastic party cups) baited with lean pieces of fish. The beetles (and, occasionally, other creatures) fall into the traps. Six days later, the traps are checked and the number and species of beetles are scored. In practice, mice or gulls can steal bait if it is not adequately secured, or fat from fish guts can turn the contents of the cup to smelly soup.

    In a perfect world, traps would be set on all of the accessible islands in the bay. In practice, time constraints forced us to prioritize. This year, we sampled Coronadito, Coronado (also known as Isla Smith), Flecha, Pata, Llave, Cerraja, La Ventana, Cabeza de Caballo, and Gemelos West.

    I made an effort this year to photograph each species using a platform with tacky wax to secure the beetle, and a scale to document its size.

    Satellite map of ahia de Lo
    Map of the bay at Bahia de los Angeles. Most islands, including all islands sampled this year, are labeled. The town of Bahia de los Angeles is labeled at lower left.

    It was marginally successful, and provided insight about how to improve future versions.

    Below is a draft guide to the beetles found on the islands, When possible, photos are provided of beetles held in fingers and mounted on the photography platform. Cartoons provide graphic representation of the relative sizes of the beetles, ranging from tiny (Batuliodes) to hefty (Cryptoglossa), keeping in mind that the sizes of all species can vary significantly.

    Distribution of each species are based on data from Sanchez Piñero and Aalbu (2002). A table extracted from their observations can be found here.

    Click the photographs if you want to see larger versions.

    Argoporis apicalis

    Medium sized, with ridged elytra and reddish legs. Argoporis is one of the few Tenebrionids on the islands which possess defensive glands in their abdomens.

    Found on all islands except Mitlan (tiny island next to Coronado).

    12 mm
    narrow black beetle with reddish legs held by fingers
    Argoporis apicalis trapped on Coronadito island. 6/26/25.
    Argoporis apicalis trapped on Cerraja island. The blurred image of an extra antenna was caused by using focus stacking to improve depth of field. 6/27/25.

    Batuliodes confluens

    This tiny brown beetle with roughened pronotum and elytra.

    Found on the majority of islands, and may be undercounted due to its small size.

    tiny black beetle on a white background
    ~3 mm
    Batuliodes confluens trapped on Flecha island. 6/23/14
    Batuliodes confluens trapped on Cerraja island. 6/27/25.

    Cryptadius tarsalis

    Small, oval, and deep-bodied, with dense rows of small punctures on the elytra.

    Cryptadius is found on Bota, Cerraja, Coronado, Jorobado, Mitlan and Pata.

    Diagram of a small beetle on a white background
    8 mm
    Cryptadius tarsalis.trapped on Llave island. Scale bar, 2 mm. 6/27/25

    Cryptoglossa spiculifera

    One of the largest beetles on the islands, with elytra decorated with rows of raised, spiny bumps.

    Found on the largest islands (Coronado, Cabeza de Caballo, but not La Ventana) as well as the rookery island, Gemelos West.

    diagram of a black beetle almost filling a white background.
    28 mm
    Cryptoglossa spiculifera trapped on Gemelos West island, 6/28/25.
    Large black beetle on blurred blue background.
    Cryptoglossa spiculifera trapped on Gemelos West island. Scale bar, 10 mm. 6/28/25.

    Microschatia championi

    Slightly smaller than Cryptoglossa, the elytra of Micoschatia are decorated with dimples rather than sharp bumps and there are punctures on the lateral pronotum of M. championi.

    Present on all but the smallest islands.

    20 mm
    Microschatia championi trapped on Cerraja island. 6/27/25.
    Microschatia championi trapped on Cerraja island. Scale bar, 5 mm. 6/27/25.

    Stibia sparsa

    Shaped like a typical Tenebrionid, with dense punctures on the pronotum and rows of punctures on the elytra.

    Stibia can be found on the largest islands (Cabeza de Caballo, Coronado, La Ventana) plus Gemelos West.

    diagram of a black beetle on a large white background
    11 mm
    small brownish black beetle held in fingers
    Stibia sparsa trapped on Gemelos West island. 6/28/25
    dorsal view of black beetle on blurred blue background
    Stibia sparsa trapped on Gemelos West island. Scale bar, 2 mm. 6/28/25.

    Tonibius sulcatus

    Very small and reddish, with relatively smooth pronotum and strongly ridged elytra.

    Described from most islands, except Coronaditio, Gemelos West, Jorobado and Llave.

    diagram of a very small black beetle on a white background
    6 mm
    Tonibius sulcatus found at Las Hamacas hotel. 7/10/24.

    Triphalopsis californicus

    Small, black, oval, and deep-bodied. Covered with fine hairs that are often coated in dust.

    Triphalopsis has been described from all islands except Gemelo West.

    Diagram of a small beetle on a white background
    8 mm
    Triphalopsis californicus trapped on Flecha island. 6/27/25.
    Triphalopsis californicus trapped on Cerraja island. Scale bar, 2 mm. 6/27/25.

    There are many other beetles, including various species of Histeridae and Dermestidae (not shown).

    Hister Beetle on Coronadito Island. Scale 2 mm. 6/26/25.

    Centipedes, spiders, and scorpions are often found in the traps in the larger islands.

    Scorpion trapped on La Ventana. 6/28/25

    References

    Sanchez Piñero, F. and Aalbu, R. L. (2002). Tenebrionid Beetles (Appendix 6.1). In A New Island Biogeography of the Sea of Cortés, pp. 129–153. New York: Oxford University Press.

  • Western Bluebirds: One Cycle Complete

    Although the screech owls have been hogging all the attention this spring, many more birds are raising families in the area. Spotted towhees, Bewick’s wrens, lesser goldfinches, and chipping sparrows can be observed singing their songs and collecting food for their offspring.

    We have been very lucky to have a clear view of a pair of western bluebirds. There has been a nest box on the back lot for many years. Last fall, it was time to replace the old, battered box with a new one, and the birds settled in early this spring.

    Female western bluebird on nest box. 3/11/25.

    They were getting things ready by the beginning of March.

    Bluebirds staking out their nest on a cold spring morning. 3/15/25.

    Despite the cold, they were ready to get started. Note the fluffed feathers in the photo above.

    Mom peeking out of the box. 4/25/25.

    The process was largely mysterious, with the parents coming and going during April and May, but no sightings of the nestlings.

    The babies finally started sticking their heads out in May. Mom and dad brought food on a regular basis/

    Nestling ready to test its wings and become independent. 5/23/25.

    By the last part of may, the kids were ready to see the world. Within a day of showing their heads, everyone was gone.

    Female starting the next nest. 5/29/25.

    I cleaned out the old nest a few days after the fledglings left, and was surprised to see a pair of bluebirds bringing new materials less than a week later. It is impossible to say whether these are the same parents, but it seems likely. They can often raise more than one clutch per year, so maybe we’ll see more fledglings in a few months.