Island foxes are masters of survival. Having lived and evolved on the windswept, rugged and relatively remote Channel Islands off California for thousands of years, cat-sized canids have quite a few tricks up their sleeves. Their small size, on the one hand, is an adaptation to their resource-limited environment. And they’re not primarily nocturnal like their mainland cousins, allowing them to hunt and feed at all hours.
Certainly, these unique physical and behavioral attributes helped the foxes recover from their catastrophic decline in the 1990s, when predatory golden eagles found their way to the islands and took up residence. In just over a decade after the eagles were expelled, the foxes went from “endangered” to “threatened.”
Researchers at UC Santa Barbara and Channel Islands National Park have now documented another tactic that hasn’t been studied as extensively: Some island foxes living along the coast have a taste for beach food. , especially the cryptic little animals that live around piles of kelp drifting on beaches, safely above the washing of the waves. These tasty creatures include beach grasshoppers (Megalorchestia spp.), which are small, land-dwelling crustaceans that live about an inch below the sand, and related species like intertidal beetles.
“We were interested in the role the beach ecosystem plays in providing nutritional support to island foxes, which are generally thought to be dependent on land-based food sources,” said Mark Page, a research scientist at the Marine Science Institute of the United States. ‘UCSB and lead author of an article published in the journal PLOS ONE.
Not all island foxes take advantage of the beach buffet, the researchers said, but the more kelp that washed up on the beach, the more available these small crustaceans and intertidal insects were – and the more likely they would be part of the fox diet. .
“The abundance of kelp and beach grubs is highly variable between different sandy beaches on the islands,” said Juliann Schamel, Channel Islands National Park biologist and island fox expert, co-lead author of the report. item. “And where there were abundant beach grasshoppers, we found that some of the foxes used them a lot.”
The researchers’ findings are the result of field investigations that searched for island fox scat or scat near the shore at 10 study sites on Santa Rosa and Santa Cruz Islands and analyzed them for content, particularly the indigestible exoskeletons of beach hoppers and other invertebrates in the area. They also used stable isotope analysis of fox whiskers collected from a subset of sites.
“Stable isotope analysis is particularly useful in differentiating between marine and terrestrial food sources,” Schamel said. Isotope analysis of fox whiskers can tell whether the food foxes eat comes from land plants (either directly or through insects and other animals that eat them), or from kelp and phytoplankton. “Examining the undersampled whiskers of known individual foxes,” she added, “allowed us to see that individual foxes foraged differently from each other, even in the same area of the island.” .
Island foxes are known to be generalist consumers, eating a variety of terrestrial foods including fruits, insects, and deer mice. Yet unlike their mainland cousins who have access to a wide variety of terrestrial foods and the ability to travel farther afield to find them, foxes on these small, remote islands are uniquely vulnerable to even minimal shocks from their terrestrial food supply.
However, the islands’ sandy beaches, where marine and terrestrial food webs overlap, are potentially rich food sources for foxes, researchers say, from sand crabs that live in the surf zone to seals and lions. of sea that occasionally run aground. , beach grubs and insects that live under the sand around washed up kelp.
It may not be so obvious during daylight hours when nocturnal beach hoppers are mostly buried in wet sand, but by dusk these little crustaceans become active and venture out in their thousands to find their favorite food: kelp that washes up on the shore. Throughout the night and into the wee hours of the morning, hordes of these crustaceans are busy on the upper beach gnawing at the kelp, leaving only traces of seaweed as the sun rises.
According to the study, the abundance of kelp wrack was the main factor explaining the abundance of beach grubs on island beaches. Beaches facing the prevailing winds and currents were able to receive large amounts of kelp which generally harbored more of these crustaceans, while beaches facing away from the wind and current generally had fewer beach hoppers on which foxes could having dinner. “On a kelp-strewn island beach, you can easily have a hundred thousand beach locusts per yard of shoreline,” said co-author Jenifer Dugan of a “prey resource that’s just ready for the predators to exploit.” land and sea animals.
The researchers are careful to point out that their study only looked at coastal foxes and not those that spent their time inland, and that there is still work to be done to determine whether kelp abundance could result in more or healthier foxes in the area. . The findings, Dugan said, suggest that beaches, with their natural connections to ocean resources such as kelp, may provide additional resilience to local populations of the threatened island fox, particularly if their terrestrial prey becomes scarce.
“It may be that in times of drought, when there is no rain for the plants that support the terrestrial prey that the foxes eat, beach food is more important to the foxes,” Dugan said. “Given that recovering populations are small and isolated, having all food options on the fox’s table is good for helping this endemic species get back on track.”
Research on this project was also conducted by Kyle A. Emery, Nicholas K. Schooler, Angela Gugliemino, Linnea Palmstrom, and Robert Miller at UCSB, and Donna M. Schroeder at the Bureau of Ocean Energy Management.
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Henry M. Page et al, Diet of a Threatened Endemic Fox Reveals Variation in Sandy Beach Resource Use on California’s Channel Islands, PLOS ONE (2021). DOI: 10.1371/journal.pone.0258919
Quote: A beach buffet: Researchers find that beach grasshoppers may be an important part of the island fox’s diet (2022, March 7) Retrieved March 7, 2022 from https://phys.org/news/2022-03 -beachy-buffet-beach-hoppers-constitute.html
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