Thursday 26 September 2013

Great Egret roost in Waterloo Region and the power of eBird

For the past two months Great Egrets have been roosting nightly at the Hespeler Mill Pond. On August 24, Ken, my Dad and I had the chance to meet up with (sort of) retired CWS researcher Chip Weseloh to try to make an accurate count of the number of individuals utilizing this roost. We weren't disappointed as we had at least 19 birds sitting out in the middle of the pond before sunrise.  Shortly after we arrived they started dispersing as is normal for these birds.
Part of the roosting flock

While this behaviour is quite common at this time of year for Great Egrets, it provides a really nice example of the utility of eBird to gather data to monitor such a roost.  This roost is especially well-suited to being monitored by Citizen Scientists because it is easy to observe and it is relatively close to a large population of birders.  In fact, since June of this year there have been at least 99 surveys done at Hespeler Mill Pond resulting in over 110 checklists being submitted to eBird!
A screen-shot showing recent Great Egret sightings at Hespeler Mill Pond
This is the really amazing thing about eBird - something as simple as going birding in your local neighbourhood can shed light on bigger questions.  In this example we can answer several:
1. When do Great Egrets start building in numbers at fall roosts?
2. When do Great Egret numbers peak at fall roosts?
3. How many individuals are using a particular roost?
4. Do numbers stay steady at a roost?

Obviously, there are many more questions that can be answered - these are just a taste. And when you think about the fact that millions of bird observations are submitted every month to eBird, the questions you can start answering are practically endless! And these are exactly the sorts of questions that scientists working for governments with increasingly fewer resources could never fully answer.

I'll leave you with this final figure showing all of the counts of Great Egrets from Hespeler Mill Pond by date for this year:

Great Egret counts from Hespeler Mill Pond on eBird

Chip Weseloh and Tyler Hoar recently published a paper where they used eBird to track the northbound migration of Great Egrets towards Ontario using eBird, I'll try to find a copy of that and post the link.

And if you aren't yet submitting your everyday bird records to eBird, hopefully this will convince you that it is more than worthwhile - every observation is a small piece of a huge puzzle!


  1. I have been monitoring this roost every Saturday morning, at the crack of dawn, for several weeks, and I submit my numbers to Chip. I have entered these sighting and others made during the day to eBird. Despite the large number of sightings referred to above, every time I post eBird gives me the message that this is an unusually high number for this date and location. (This happens for other sightings too, of Great Egrets and other species, where clearly recent trends indicate a lack of rarity). It begs the question: How often does eBird update its parameters as to what is considered rare or abnormally high numbers on a given date? Seems to me - not too often!

  2. Hi David,

    eBird doesn't update the filters, that is done by real human beings. The way it works is there is a set value for each county in Ontario for each species for each day of the year. You have to remember that a) the filter is the same for all eBird users, no matter their expertise level and b) we can't adjust the filter for small areas (i.e. we can't have a separate filter value for Hespeler Mill Pond - it is just too complex of a task). So, my answer to you would be that the parameters are updated whenever the volunteer reviewer notices that they need updating, but in your situation that isn't the case, since outside of this one small area in Waterloo Region seeing more than just a few Great Egrets is an unusual count.

  3. Hi Mike:
    Thanks for the explanation.
    I am surprised, however, that you categorize Hespeler Mill Pond (Ellacott Lookout) as "one small area in Waterloo Region seeing more than just a few Great Egrets...." Laurentian Wetlands has been consistently reporting at least 14 to eBird; the last time I checked the downtown Cambridge roost with Bill Read there were 11 roosting in trees along the river. I believe there are other locations too. I am not sure, however, how many of these locations have eBird subscribers.