Thursday, November 8, 2012

Massachusetts Owl Forecasting using historic eBird Data

As stated earlier in the week, I finally have my owl forecast done so figured I'd share it as there's some pretty interesting stuff in it as you will see.  All of this eBird data is for the state of Massachusetts and is from Jan 2001 to Dec 2011.  The first table shows the total owl reportings by month and what I found most interesting seeing it this way is the month of May being the highest reported month followed by December and January.

So naturally the next thing I'd want to see is what owls drive what numbers and I'd break it out for the state as well as Worcester County.  I'll let the tables speak for themselves instead of rambling but was somewhat taken aback with the high April and May numbers for Great Horned Owls and based on species notes- I'm guessing those sightings are driven by recently fledged owls and parent contact calls.   I'm also guessing the high reports of Barred Owls may be due in part to the same.  You'll also notice the high number of Northern Saw-whet Owl reports in October with most of it being driven by Worcester County.  I decided to look at those numbers to the see impact of duplicates, and it's minimal so these are reports coming from individuals as well as monthly totals for Chickadee records in association with Strickland's banding project in Uxbridge.

And now a look at total Massachusetts by owl and county with Middlesex County having most reports of owls, followed by Essex County. Interesting to see Worcester County coming in at number two for Barred Owl sightings overall.  Also interesting to see many of the common owls on neither Nantucket or Martha's Vineyard and cuious to know why but guessing it may have to do with lack of prey or fear of water?).  Also wondering if the the small owls like Nantucket and Martha's Vineyard due to the fact the larger owls  for the  most part are non-existent so they feel more secure in hunting/calling so are seen or heard more often.  (Sounds reasonable to me as the only place I've ever been lucky enough to hear a calling Saw-whet is on Nantucket during a CBC)

One of the things I was hoping the data would tell me is what environmental conditions yields the most reports as we all know owling isn't as easy as other forms of birding and it's often done in the dark during the cold, long days of winter so your'e better off planning ahead instead of freezing your butt off listening and looking for owls who never come.  So the first thing I did was look at owls in association with lunar cycles.  Note:  Lunar cycle info does NOT come from eBird but rather my own lookup tables I created to help me crunch the numbers more.

This may be surprising to some, considering many of us have been told or experienced the best time for owls is during a full moon but as you can see that's not always the case and the numbers all seem fairly close with minimal impact.  So is the full moon theory incorrect?  Maybe it is, but not with this data (hows that for an answer HA).

The eBird tables above is sample data (meaning species notes indicated if it was seen or heard) and is broken out first by reports of call only, and 2nd by seen and the full moon doesn't rank first or second on either of them!  If you look at it at a species level with Northern Saw-whet Owl in particular you'll see it's most vocal during a full moon but mostly sighted during a quarter moon so what gives?    Well according to survey's I've seen of the Saw-whets, many owl survey participants get a better call back rate during a full moon (others are inconclusive) so that would indeed make sense.  Sightings are mostly related to Uxbridge owl banding with most sighted reports happening during a New or 1st Qtr moon.  This data is somewhat conclusive with studies conducted on these birds and banding projects elsewhere.

Source:  Northern Saw-whet Owls & Lunar Cycles.  You will see in the chart above that full moon captures happen least during a full moon and there's a theory on why.  The  theory (included in the link), speculates that since these small predators are also prey  they hide more during a full moon and prefer less moon light during the other lunar cycles where there's darkness to avoid being eaten of course!  The other interesting owl of note is the Short-eared Owl who uses the full moon for hunting which this bird has been known to do so nothing surprising there.

So in summary, owling during a full moon may make it easier for you to see the owls and there have been studies  that shows a full moon yields the most owl reports, but the data above doesn't show that in our neck of the woods so take it as you will.

If your'e still awake, then let's move onto the next way I looked at the data which is time of day.  This was calculated using "Observation Start Time", and you will see a category called casual and that is when there is no beginning time given so just ignore that for the purpose of this analysis.  I won't ramble much but just note that you don't really have to get out before 3AM to owl unless you have a really strong urge to do so!

Broken out the same way but by owl with 6 to 9 AM having the most reports followed by 3 to 6AM and 3 to 6PM so no surprises there as all categories fall into the before and after dusk.

And just when you thought I couldn't get any geekier I prove you wrong as you will see in the data below which shows owl sightings by cloud cover!  Woot!!  IMPORTANT TO NOTE:  This table is my weather underground  lookup table for Worcester which I used to map the eBird data by Worcester weather so it's not 100% correct as it could be cloudy in Worcester by partly clear in Plymouth, but it's close enough for the exercise.


Broken out by the state level as well as Worcester county and as you can see the clearer the skies, the better probability of success.  Also note how close Worcester County is to the state % wise for each category despite it only having 524 of the 8,120 counts which I thought was pretty darn impressive!  You'll also notice you can see/hear owls during cloudy conditions and I believe a lot of those numbers in that category are coming from CBC counts when it's always cloudy and did I mention cold!


And lastly broken out by wind (used mean winds and kph) and the tables above are no surprise with most reports of owls coming in with less than 10 kph, followed by the 10-20kph and nothing coming in after 21kph.

Are you still with me and awake???  Good because now come the summaries!

Table above summarizes most of the above making for a nifty resource to have when your'e itching to do some owling!!

And finally this which is a summary on info of Massachusetts owls coming from Mass Audubon Owls.

And now I leave the rest up to you and encourage you to use this data next time you're out there looking for owls!!!  The only thing I ask in return is you submit your observations to eBird if you're using it.  We often think of it as a nice tool to have for managing our yearly lists and life birds, but there's so much more to it besides that as you have seen in the tables above and something I am most grateful for.

Take care all.


Bob Hilscher said...

Hi there. Good to see you have so many Saw-Whet Owls in your area. I live in Toronto, Canada, and two weeks ago, my wife, Jean, and I came upon an adult Saw-Whet Owl out in the bush. This was the first time as birders that we had ever seen a Saw-Whet Owl. Fortunately, we had our camera with us and got some good pictures and video. We have posted them for anyone interested at:

Kim said...

Bob, thanks for the comment and visit and a BIG THANK YOU for the link!!! LOVE the video and pictures. Such cute, tame little birds and I've only been lucky enough to see one banding but would love to have your luck seeing it in broad daylight. The ones we get here for the most part are migrating through so never a guarantee which makes them even more special.


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