Recently, members of the Fatal Light Awareness Program (FLAP) were invited to hear the results of Toronto Hydro’s study on bird mortality performed at the Exhibition Place wind turbine.
It’s certainly heartening to see that Toronto Hydro is taking the issue of bird mortality into account. However, based on the data that FLAP has collected over the years, we had some concerns about the dynamics of the study that may have influenced the number of casualties observed.
The fall migration portion of the Turbine study was completed on the 27th of September. FLAP data indicates that 67% of the birds we encounter each year are salvaged during fall migration periods. Seventy percent of collisions recorded by FLAP during this period occur from the beginning of October through to mid-November. Many of the species that we encounter during this period don't pass through the Toronto region in large numbers until late September. What's most alarming is that 9 of FLAP’s 10 most frequently encountered species are salvaged after September 27th. To add to this concern, 6 of these 9 species are most often salvaged throughout the month of October than at any other time of the year. Therefore, an observer at the Turbine site would have missed the most opportune time to observe those species more vulnerable to collisions.
FLAP’s 10 Most Frequently Encountered Species
BOLD text indicates species encountered after September 30
Italic text indicates species most often encountered after September 27 than at any other time of the year.
White-throated Sparrow
4413
Ovenbird
2547
Golden-crowned Kinglet
2279
Brown Creeper
1199
Ruby-crowned Kinglet
1136
Common Yellowthroat
1118
Dark-eyed Junco
1054
Hermit Thrush
988
Magnolia Warbler
641
Nashville Warbler
612
FLAP recounted these concerns to Dr. Ross D. James, one of the authors of the wind turbine study. In his response Dr. James indicated that he feels most of the healthy warblers are gone in September. He suggested that the warblers we pick up later in the season (i.e. the common yellowthroat and Nashville warbler) might be stragglers that are less healthy and more likely to collide with buildings. However, warblers that FLAP encounters throughout October tend to be healthy inexperienced juveniles. We believe that it would be valuable for the Royal Ontario Museum to inspect our Fall 2003 casualties to find the ratio of juveniles vs. adults, and to compare fat condition with earlier migrants.
Dr. James also presumed that the October casualties observed by FLAP were largely due to nocturnal collisions. The majority, however, occurred as a result of daytime collisions. Last year, for example, we collected a total of 189 warblers throughout the month of October. Of these, 162 were collected during the day; this represents 86% of collisions.
We also had some concerns about how scavenging was observed at the Turbine site. Each year FLAP volunteers witness 100+ birds that are scavenged, the vast majority by ring-billed gulls. We have observed these gulls removing casualties within seconds of initial impact. The gulls often arrive within an hour before daybreak and continue this activity until dusk. They leave behind little or no trace of a collision ever occurring. At the same time, they don’t appear to be interested in scavenging carcasses that have been on the ground for more than a few days. Therefore, there would be little evidence (no tell-tale feathers) from birds that had been scavenged on days where an observer was not present, whereas planted carcasses might remain untouched. However, we feel that we don’t have enough information about the scavenging habits of gulls to make a solid conclusion in this regard.
While studies like this are admirable, the above factors deserve careful consideration, as they may have had a negative impact on the results of the wind turbine study. In light of these concerns, we feel that this study should not be used as a template for future wind turbine site studies.
Sincerely,
Michael Mesure
FLAP Executive Director