[Tweeters] Bald Eagle peep show....(long)

Martin Muller martinmuller at msn.com
Wed Mar 9 21:34:15 PST 2016


Your observations are very interesting. The observation of an immature bird helping feed young is worth writing up and having published.

Here’s what the Birds of North American (online) says on the subject:

"Cooperative Breeding
On Amchitka I., AK, 2 different nests had 3 adults in attendance in 2 separate years, and 3 adults were reported at 3 nests in 1 yr (Sherrod et al. 1976 <http://bna.birds.cornell.edu/bna/species/506/articles/species/506/biblio/bib260>). Fraser et al. (1983 <http://bna.birds.cornell.edu/bna/species/506/articles/species/506/biblio/bib106>) reported 3 adults at the same nest in Minnesota over a 3-yr period. Sex of third individual unknown. In Connecticut, extra male delivered food to nestlings but generally avoided interactions with pair (Hopkins et al. 1993 <http://bna.birds.cornell.edu/bna/species/506/articles/species/506/biblio/bib169>). In California, extra female assisted with incubation and food provisioning of young; was tolerated by pair. Low numbers of adult males may have provided incentive to female for cooperative venture (Garcelon et al. 1995 <http://bna.birds.cornell.edu/bna/species/506/articles/species/506/biblio/bib110>)."

Source: Buehler, David A. 2000. Bald Eagle (Haliaeetus leucocephalus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/506 <http://bna.birds.cornell.edu/bna/species/506>
doi:10.2173/bna.506 <http://dx.doi.org/10.2173/bna.506>

I did a quick check of Stalmaster’s The Bald Eagle (Universe Books, New York, 1987) but did not find any mention of cooperative breeding. I don’t have my copy of Gerard and Bortolotti (Gerrard, J. M. and G. R. Bortolotti. 1988. The Bald Eagle: haunts and habits of a wilderness monarch. Smithsonian Inst. Press, Washington, D.C.) handy, but it would be good to check that out on the subject too.

Does anyone in Tweeter-land know of any reports of this?

As to your almost certainty that it’s “the kids” coming back in following years. How do you determine that? Are they tagged or otherwise marked?

We’ve been studying Peregrine Falcons in Seattle and banding their young. We’ve seen youngsters food begging in late-winter (when they are supposed to be independent), and in one instance the adult male actually fed the food-begging immature female. However, that female was un-banded while we put bands on all of his offspring. So even receiving food from an adult is no guarantee of kinship (and I’m extrapolating from peregrines to Bald Eagles here).

I’ve seen winter battles over food with immature birds making some pretty serious-looking attempts at stealing food from adults (or other immatures), which, had the adult not relinquished the food might well have resulted in the adult getting injured. I’ve never seen an adult give up food to an immature without a fight. Were you referring to adults passively relinquishing food to immatures or were you also referring to immatures threatening adult and taking the food by force?

For all I know the longer feathers on young bald eagles not only give them an advantage soaring, it also makes them more imposing so that during battles over food they get to win occasionally, to make up for their lack in skill to procure enough food for themselves during this high-mortality stage of their lives.

I did a quick check on the Lake Casitas eagles (which I was not familiar with). Found a 2015 report about an adult female wounded during territorial battle (with pretty gruesome picture), but it was only a partial report. I didn’t feel like signing up to read the rest. Maybe you can summarize?

Martin Muller, Seattle
martinmuller at msn.com

> On Mar 8, 2016, at 11:25 PM, Sammy Catiis <Hikersammy at msn.com> wrote:


> Just as a note of possible interest, I've witnessed almost certainly the kids coming back to the nest the next year. Sometimes landing IN the nest.. and sometimes even being still fed by the parent. Or more like supplemented. There is one instance where I seen that the kid actually stuck around and helped feed his new hatched brothers and sisters.. I've only seen that one time in a nest in Snohomish, but I'm sure it happens more than we realize. When it comes to Eagles, there is no certainty is there. They don't mate for life always and may even step out of the relationship when given a whole lot of eagles in an area . I think for some areas, we are just more used to there being less eagles & more competition which keeps the kids away from returning and more battles for nesting areas. Just my two cents.. :D I have watched many parents during the Winter keep other Eagles away from a catch and call and call, just to move aside for a 1st year, which I can only assume is theirs. In most observances, the young come back to the area just to be chased away from the nest. Tough Love I suppose. If you don't know of the Lake Casitas story last year.. it may be of interest.


> Sammy

> Arlington


> ________________________________________

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