Tuesday, March 20, 2018

More Connections Between Bald Eagles and Island Foxes

courtesy of P. Sharpe; bald eagle catching fish off the islands
The recovery of bald eagles on the California Channel Islands has played an important role in island fox recovery. Bald eagles prey on fish and marine birds. They are not mammal predators and do not actively hunt island foxes. Because bald eagles nest on the Channel Islands, they chase away migrating golden eagles and do not allow them to colonize the islands.

With 50-60 bald eagles now living across the eight Channel Islands, no island foxes are known to have been killed by golden eagles for several years. Bald eagles definitely make a difference in the ecosystem for island foxes. But what benefit do island foxes provide bald eagles?  

Across the Channel Islands bald eagles are hatching out their 2018 chicks. Channel Island National Park reported that there are 13 active bald eagle nests across the islands this year and at least 22 known eggs.  

courtesy P. Sharpe
Three eaglets hatched in the Sauces Canyon nest last week on Santa Cruz Island. You can watch them 24 hrs a day via a webcam https://explore.org/livecams/bald-eagles/channel-islands-national-park-sauces-bald-eagle

Tonight, close observers saw some unexpected visitors to the bald eagle nest. Along with fish, the parent bald eagles have brought scavenged seal placenta back to the nest to feed their chicks. But with the darkness, something else stole up into the nest to eat the placenta bits. Circled in green, do you see the surprise scavengers? island deer mice.

captured image from the webcam 3/20/18
Who would have thought that hungry deer mice would come up into the bald eagle nest to eat meaty placenta. The eagle does not have night vision, it is a daytime hunter. It could hear the munching mice and would occasionally drive them off. Island deer mice are known to eat songbird eggs, and possibly chicks, when given the opportunity, (like when island fox populations were very low). The eaglets are small and without their parent's protection, would they be prey for the gang of deer mice? At one point six deer mice were visible.

Island foxes play an important role in controlling island deer mouse populations. 

Other bald eagle parents on the islands are sleeping soundly tonight, but the bald eagle with the messy nest is wide awake in the rain. It has two jobs tonight: keeping three eaglets warm and dry, and keeping the deer mice at bay. It will be a long night for this bald eagle, it needs an island fox.

Island foxes sometimes clean leftover food out of bald eagle nests. Island fox in a bald eagle nest.

Friday, March 09, 2018

Sex and the Single Island Fox

When it comes to reproduction, island foxes are not your typical canine. 

A female dog will go into heat and become reproductively receptive even if there is no male dog nearby. Dogs have spontaneous ovulation, they have a determined reproductive cycle which includes a spike of hormone to release the ovum or egg into the female's reproductive tract. Not so with island foxes. 

Captive breeding occurred from 2000 - 2008
During the period of captive breeding to increase island fox populations, it was discovered that female island foxes, without access to a male partner, did not show the elevated hormone patterns signaling they had ovulated. These single females did not go into heat.

A similar reproductive behavior occurs in members of suborder Feliformia, or the cat branch of carnivores (cats, otters, wolverines, ferrets, etc.), and in bears. These species have induced ovulation–some physical or hormonal stimulus from the male is required to stimulate or initiate ovulation.

To date island foxes are the only canine observed to have this reproductive trait. However, research on this facet of reproduction is minimal. It is unknown if gray foxes, the ancestor of island foxes, are induced ovulators. 

Gray foxes (Urocyon cinereoargenteus) are an ancient species. Some sources consider them the most basal or closest to the root of the canine family tree. In Decline and Recovery of the Island Fox the authors suggest induced ovulation may be a primitive trait shared between these ancient canines and other carnivores, like cats and bears. Spontaneous ovulation may have evolved later in the branches of the canine family tree that gave rise to red foxes and wolves. Compare gray fox and island fox.

The single female island fox? 

Well, she just doesn't waste her reproductive energy if there is no eligible mate at hand. 

What other animals are known to have induced ovulation? rabbits and camels

Friday, March 02, 2018

Fox Foto Friday - Island Foxes in Art

To know island foxes is to love them. This charming wedding cake duo topped the nuptial cake for one of our favorite island fox biologists. 

From cakes to wood carvings, ...

...island foxes are gradually making their way into culture and consciousness.

If you think about it, island foxes are a pretty good totem for marital happiness: they are more monogamous than humans and form very strong pair bonds. Males and females are devoted to family. More about island fox behavior.

Pair during captive breeding period

More island foxes in Art:
The Art of an Ecosystem - interactive art on the island fox story
Student Art & Conservation Project