Public Closures on Anacapa Island
Certain trails are temporarily closed on Anacapa Island to all public entry for the protection of breeding western gulls. More »
San Miguel Island Closure
In the interest of public safety, the U.S. Navy is closing San Miguel Island until further notice due to recent concerns of possible unexploded ordnance. More »
Island Deer Mouse
Quick and Cool Facts
Island studies have shown that deer mice occasionally prey on eggs and nestlings of Scripps's murrelets on Santa Barbara Island. However, the annual reproductive success of murrelets was not related to deer mouse densities. Likewise, research on San Miguel Island showed that as seed predators, deer mice had limited impacts on giant coreopsis populations, especially when compared to the negative competitive effects of non-native annual grasses.
Park research has shown that island deer mouse population densities are higher than anywhere else in the world. However, population dynamics on different islands vary in response to numerous factors, including predator diversity, vegetation community structure, and climate.
For example, monitoring data shows that deer mouse densities on San Miguel Island are strongly limited by the endangered island fox (Urocyon littoralis littoralis), whereas on Santa Barbara Island, where there are no foxes, mouse densities are much more variable. Predation by barnowls on Santa Barbara Island can drive th emousr population to extreme lows. Unlike the generalist island fox, barn owls are more specialized predators and do not switch to other prey species when their their primary prey (mice) decline.
In addition, research has revealed that rainfall is a strong driver of deer mouse population dynamics. High winter rainfall encourages plant growth which provides food resources, while drought reduces plant growth and limits mouse productivity. However, abundant winter rain combined with cold temperatures may actually increase winter mortality and reduce the number of mice that survive from fall to spring.
Deer mice populations at Channel Islands National Park have been monitored since 1992. Nine permanent grids have been established in various habitats on Anacapa, San Miguel and Santa Barbara Islands. These grids are sampled twice each year during the spring and fall seasons and mark/recapture methods are used to determine population densities.
The objective of the monitoring is to identify trends in the deer mice population, evaluate the general health of the population utilizing weight, age, sex, and reproductive information and to increase our understanding of how island ecosystems respond to changing environmental conditions.
Did You Know?
Park and sanctuary waters are home to the largest aggregation of blue whales in the world. Approximately 10% of the global blue whale population gathers in the channel during the summer. More...