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The Restoration of the Island Fox

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The Captive Breeding Program
Captive breeding was a necessary - and ultimately successful - recovery action for island foxes, and it also provided an opportunity to study island fox reproductive biology, which was previously unknown. When foxes were first brought into captivity on San Miguel Island just before the 2000 breeding season, mated pairs were established by placing together males and females that appeared likely to have been paired in the wild, based on information available at capture. Because there were more females than males, some females were housed together.

In subsequent years as pups were born and reached maturity, they were assigned mates based on a computer program designed to prevent inbreeding in small populations, such as the fox, and maximize genetic heterozygosity (lack of similarity).

The success of the island fox breeding program is evident in data given in the 2011 Island Fox Meeting Report. Considering the northern Channel Islands exclusively, numbers that include pups are as follows: Santa Cruz, 1302; San Miguel, 516; Santa Rosa, 292.

As a result of research conducted during the captive breeding period, we now know that island foxes have induced estrus and ovulation, which is unique among canids and may be related to other distinctive features of their mating system. Island foxes differ substantially from wolves, the species perhaps best known for its complex social system, strong pair bonds, and solicitous parental care. All the canid species appear to be socially monogamous, but from there they diverge in terms of group size, degree of sociality, and age of dispersal of young. For example, male aggression toward females - something that appeared rather common even in the reproductively successful island foxes - is virtually unknown for other canid species, in which males tend to be very solicitous to females, especially during estrus and pregnancy. However, it is unclear whether this behavior is characteristic of free-ranging island foxes or merely an artifact of captive conditions. In another contrast with other canids, the reproductive rate was lower for captive-born island foxes, the opposite of what is usually observed in other canid species. This suggests that something, such as social experience during the juvenile period, might have been missing in the captive environment, something that apparently is less important to other canid species.

Reintroduction of the Bald Eagle
The process of bringing back the bald eagle to the northern Channel Islands led authorities to believe that they might prove to be a natural deterrent to the colonization of the golden eagle. In 2006 a bald eagle was observed escorting a golden eagle out of its territory on Santa Rosa Island. Newly released bald eagles were also seen chasing golden eagles off of a carcass provided for them. Historical evidence and studies have shown that the natural bald eagle food sources are marine fishes, seabirds and pinniped carcasses, suggesting that bald eagles pose little threat to the island fox.

From 2002-2006, the Institute for Wildlife Studies (IWS) released 61 bald eagles on Santa Cruz Island. In 2006, the first known nesting attempts occurred in the northern Channel Islands. Two pairs of eagles successfully fledged one chick each from nest at Pelican Harbor and Malva Real on Santa Cruz Island. Since 2006, there have been successful hatchings and Santa Cruz and Santa Rosa Islands. As of 2012 there are over 50 bald eagles on the California Channel Islands and over 30 known eagles on the northern Channel Islands.

Encouraging Native Plants
Island foxes evolved in an environment thick with native shrubs that later dwindled after the introduction of livestock grazing. Without shrubs for hiding cover, the foxes were especially easy for the golden eagles to catch. Today, the removal of nonnative grazers is showing astonishing results. Lush shrubs and wildflowers are coming back. Restoring the island's vegetation benefits the foxes and all native wildlife.

An Eco-system Solution
Without the ecosystem-level changes of pig removal and bald eagle restoration, fox recovery was not assured. That those two ecosystem level actions were implemented in conjunction with island fox recovery actions was fortuitous. The two actions had been planned and funded separately from island fox recovery, but the value of those planned actions to island fox conservation was recognized when the complicated relationship among foxes, pigs, and eagles became apparent. The success of those ecosystem-level actions was facilitated by the islands' isolation and their limited, more defined ecosystems: once pigs were removed from the islands, there was little chance of them returning. The success of these ecosystem-level actions for island fox conservation underscores the importance of considering ecosystem-wide conditions in endangered species management.

Did You Know?

Island deer mouse

The endemic island deer mouse is the only native terrestrial mammal common to all the Channel Islands and is larger than mainland deer mice. Densities of deer mice on the islands can be greater than anywhere else in the world. This makes you happy if you're an owl, but not if you're a camper.