Hello, and welcome to the 2012-13 Season!
It is the beginning of a brand new winter of counting! Even though Sunday’s weather did not feel like winter, the eagles actually behaved as if it were. Thirty-nine eagles were tallied flying in to roost under very warm temperatures.
As usual, when the river is free of ice, the birds were found in roosts mostly downriver, this time at Jones Slough and at Lone Rock. The two birds seen at Ferry Bluff could easily have been the local breeding birds that nest near the bluff, with a similar explanation for two birds seen at Leland.
Normally, when evening temperatures remain above freezing, eagles often roost near their feeding area in non-traditional roosts, often scattered trees. It is only in colder weather (i.e. below freezing) that traditional roosts are used more consistently by groups of eagles.
Evidence of the trend for eagles to use traditional roosts at lower frequencies when the weather is warm comes from a comparison with previous counts. Recent past winters have been considerably colder and 62, 115, 59, 104, 314, 198 and 187 eagles were seen during our first count of the winter in the respective winters of 2011, 2010, 2009, 2008, 2007, 2006 and 2005. The last time our first count of the winter was less than 40 individuals was a decade ago in December, 2002. We counted 25 eagles during the first count that year.
Of course, it is possible that birds have not migrated to our area as of yet. It is hard to distinguish between this hypothesis and that of the effect that warm weather has on roost behavior. We do know, from our previous radio-tracking studies, that telemetered birds showed a similar response to warm, night-time temperatures. On nights above freezing, telemetered birds tended to use non-traditional roosts and perched through the night within several hundred meters of their foraging area of that day. On nights that were below freezing, however, telemetered birds tended to use traditional roosts more frequently, even when these roosts were several kilometers away from their foraging area. The traditional roosts are the roosts that we observe during roost counts.
This data, as in past decades, is very important to collect each winter. It is a way of monitoring our local population of birds. It also teaches us more about the winter ecology of eagles which, in turn, is used to provide advice on a wide range of eagle conservation issues. Our count data has been used to advise development projects, power line pathway locations, timing of bridge repair work, the potential impact of disease outbreaks (e.g. when West Nile first began to affect eagles in WI) and land purchases. Thirty-two hours of volunteer effort were required to tally this first count of the winter alone.
Clearly, we need your help to collect data! Currently, three different roosts still need count coordinators and we need new counters as well. Without your assistance, without your willingness to be involved, we cannot conduct these important counts which have occurred since 1988. Please contact me if you wish to help. All necessary training will be provided. I can be reached either via email or at 608-544-2107
Thanks for your consideration, and good counting this winter!