Monday, March 24, 2014

Canada Goose Update

The goose and the hawk. Hawks drive the
intruder from their nest.
In the last blog, I speculated that Wilma's nest intruder could have been dumping eggs. It looks like she dumped not one, but two! From Eaglecrest:

Canada goose Mom Wilma is incubating NINE EGGS...seven of her own and two laid right in her nest by a female intruder. The two "foreign" eggs were laid on 3-15 and 3-22. In both cases, Wilma relentlessly attacked the intruding goose until she left. We may not have seen the last of her. The two intruder eggs will not hatch with Wilma's...they are eleven days or more behind schedule. Wilma began full time incubation of her SEVEN eggs on Tuesday, March 4th. We will expect the little goslings to hatch around March 31st...with the "big jump" about April 1st. Mate Fred is in constant protection mode, as usual.

We've been asked why this goose is behaving so strangely. Why is she dumping eggs? Why is she trying to sit in a hawk nest? I'm speculating that our invader is responding to the recent death of her mate. I haven't seen her accompanied by a male, which is extremely uncommon. Mated male geese are almost always hovering around their nesting mates, protecting them from predators and other geese. A study done at Horicon March in 1959 indicated that reduced breeding productivity was almost entirely connected with goosey social behavior. The authors of the paper wrote: 

"Over half the birds assumed to be capable of breeding failed to make nests in which they laid and incubated eggs; one-fifth of the birds failed even to pair up effectively. The nine pairs that failed to lay eggs in nests were involved in unusually frequent territorial clashes, and most of them were unable to maintain stable territories for any length of time. Four of the 5 pairs (and perhaps all 5) that lost their clutches did so because of disturbance to the female from other geese, related to a lack of effective male defense."

So our unknown intruder doesn't have a male to help safeguard her nest from other geese, who can be very disruptive to laying and sitting. What seems like erratic behavior is really an attempt to produce young under extremely difficult circumstances. While the intruder's eggs won't survive this spring, she'll most likely pair up with a new male goose to try again in 2015. There is no shortage of geese at Eaglecrest!

Geese have an elaborate, shifting hierarchy ruled by ganders with large families. I'll write a little more about the importance of family once the eggs start hatching. To watch Eaglecrest live, go to http://www.ustream.tv/eaglecresthawks. We anticipate hatch in Wilma's nest at the end of March or very early in April. 



Resources

Social Behavior and Breeding Success in Canada Geese (Branta canadensis) Confined under Semi-Natural Conditions
Nicholas E. Collias and Laurence R. Jahn
The Auk
Vol. 76, No. 4 (Oct., 1959), pp. 478-509
Published by: University of California Press
Article Stable URL: http://www.jstor.org/stable/4082315

Some of what we're seeing could also be a response to crowding, which impacts reproductive and social behavior. As California's drought reduces water resources, birds and other animals crowd more densely around those that remain. We'll explore the impact of crowding in a future blog.

1 comment:

IleanaDU said...

So what will happen to the intruder's eggs after Wilma's eggs hatch?