February 28, 2010 Eagle Roost Count

Posted by gengberg on March 3rd, 2010

Hello all of you stalwart eagle counters:We counted 54 eagles on our last count of the season this past Sunday. That is 11 more than we counted on Feb. 14 and 5 birds less than the late and mid January counts. Outside of the 101 eagles counted on January 3 we have actually ranged from 43-59 eagles for the whole winter. With the warm weather during this last count I expected that we would count far fewer birds than we did. During the radio-tracking study we often noticed that, on nights where the temperature remained above freezing, eagles would often roost at night in any trees located close (less than 500 m) to their foraging sites and not use traditional roosts. Our count last Sunday was fairly warm so I thought that this would be the case as well. Lone Rock Roost counters did observe many birds flying further west from Lone Rock Roost, suggesting that the river is certainly open downstream and are thus using other roosting sites that we do not monitor. Theory aside, our roost count was actually quite comparable to other counts and the warm weather did not appear to affect roost flights the way that I thought they would.

Also of note, the eagles counted flying into Ferry Bluff were not seen flying into the traditional part of the roost on the northeast side of the bluff but rather to the river side (south) of the bluff. Next year will need to organize roost counters to count Ferry Bluff from several vantages so that we can determine where exactly these birds might be roosting. This would constitute a very new part of the Ferry Bluff Roost complex that eagles are using. A similar approach is taken to counting eagles flying into Lone Rock Roost as well. Three groups of observers surround the roost areas and watch as birds fly in from the west, south and east. In Lone Rock’s case, however, no one actually sees where eagles actually land to roost. Our radio-tracking data are the only data that indicate that.

Reece Donnihi also reported that Ederer/Been Roost had the most eagles of the year (10 birds) using the roost but these birds perched in a very different part of the roost on Sunday. They were located primarily on the east side of the valley rather than being tucked into their normal spot at the northwest end of the roost. Again, this part of the roosting valley for Ederer/Been has never been used by eagles during our roost counts and none of our radio-tracking locations came from this area of the roost either.

Finally, as most of you have seen, understanding how eagles respond to food sources and other attributes of their winter habitat is a key reason for why we keep doing these counts. Over the summer I will try to re-examine the DNR fish data from the river in relation to various measures of eagle use of the Lower Wisconsin River Valley during winter. Originally I used maximum eagle counts each winter to compare to fish number and biomass sampled during the preceding summer. Our counts from this winter, where one count was twice the rest of our counts, suggest the error of that approach to analysis. The 101 birds counted on one day do not reflect the relatively lower eagle use that occurred during the entire winter. Perhaps I should use a measure like average eagle number during all 7 counts from each winter and compare that to fish data. I will let you all know what I find.

Thank you very much for your efforts on behalf of eagles and on behalf of our community. I hope to work with you again next winter if not sooner.

Jeb

Count Results:

Adult Imm. Unkn. Total

Blackhawk 4 2 6

Sugarloaf 0

Ferry Bluff 3 1 1 5

Fox 2 2

McDonald 0

Jones Slough 0

Lone Rock 7 10 4 21

Big Hollow 0