The Decorah Eagle parents surprised us and have begun building a new alternate nest for themselves. This is not uncommon for eagles to do. In lieu of them building a new nest, we are unsure if they will return to the previous nest for the 2012-2013 season. We are unable to place cameras at the new site for this upcoming season as it would pose a serious risk of scaring them away. If the eagles adopt the new nest for this season, and next, we will look into placing cameras at the new nest location for the 2013-2014 season.
While we may be disappointed that we may not be able to view them for this season, we are excited for them. Their health and welfare continues to remain the most important aspect in all of this. We are uncertain at this time which nest they will choose to lay eggs in, but by the end of November we should have a better idea, and we will keep providing updates.
Decorah eagle in new nest
So why would they invest the time and energy to build a new nest when the old one remains perfectly serviceable as far as they can tell? Several hypotheses have been proposed to explain it:- Alternate nests may serve as 'insurance'. If the occupied nest is destroyed or rendered unusable, the eagles can quickly occupy the alternate without having to build a new nest.
- Changing nests from year to year helps the eagles avoid parasites and 'nest mates' who are attracted by the food the eagles bring in.
- Shifting nests from year to year may help the eagles avoid parasitism. The additional nests may be a way of marking territory.
- They warn other breeding pairs away and demonstrate fitness on the part of resident adults.
- Eagles like to build nests.
Although they haven't seen it in Decorah before, multiple nest building is a relatively common activity: in most but not all instances bald eagles will have more than one nest in their breeding territory. In one study of 924 territories, eagles were found to have an average of 1.5 nests in their breeding area.
In another study of 318 territories, 45% of eagles had two nests or more (Stalmaster, 1987). Eagle nests can be classified as active (shows or showed evidence of breeding by bald eagles during the current or most recent nesting season), alternate (intact or partially intact and used by bald eagles at any time during the past five nesting seasons, but was not used during the current or most recent nesting season), or abandoned (inactive through six or more consecutive nesting seasons). It takes six years for a nest to go from 'alternate' to 'abandoned', since last year's alternate nest might become this year's occupied nest.
Why?
Only the eagles know for sure!