Wednesday, 10 October 2012

Cool stuff about rarities

Another few days has passed without any megas showing up in Ontario. Is it just me or has it been sparse for rarities the last month or so? While there have been a few interesting things showing up, most of them are either not countable for the year list because they are considered subspecies (Harlan's Hawk, Vega Gull) or because I already had one for the year (Scissor-tailed Flycatcher, Western Grebes, etc)! Then of course there was the Eurasian Collared-dove chase which turned out to be a domestic Ringed Turtle-dove. What it all boils down to is that I have seen just one year bird since September 12. Where are the Western Kingbirds? But that should change soon as the continuous strong southwest winds ought to blow something interesting in! A few potential year birds have been seen the last couple of days - the season's first Purple Sandpiper at Presqu'ile yesterday, and a Red Phalarope briefly at Sault Ste Marie a few days ago.

I was bored a few days ago so I decided to go through the OBRC data and make some graphs. Most people assume that mid May is the best time of the year to see rarities, with the period from late September to early December generally agreed upon as the "best" rarity time in the fall. I decided to look at all the records of rare birds accepted by the Ontario Bird Records Committee to get a better picture of when rarities show up in the province.

For all of these graphs, I used all accepted records from 1997 to 2010. I didn't pick 1997 for any specific reason, it is just that I wanted some sort of cutoff since it is somewhat labor intensive working with these data. I only used accepted records, and I didn't include records in which the species identification was correct but the bird had an "uncertain origin". Here is the first graph - all of the accepted rarities by week of the year. Of course, click on the image to see it full-size.

A few interesting things stick out. The first obvious thing is the number of rarities that show up in the spring compared to the autumn. I knew May was good, but I didn't know that in the middle two weeks in May, at least 3 times as many rarities showed up than in any week in the autumn (except the first week of November).

Additionally, some weeks were amazingly dead. In the 14 years I graphed, the OBRC has only accepted 2 records from birds that were found between February 19 and 25! Compare that to the 130 accepted records of birds found May 7 to 13. The whole period from late January to late March is essentially useless for rarities in Ontario. The period from mid June to mid August ins't much better!

The next interesting thing was the first week of November. Why is there such a huge jump for this week? Looking at the data, I could see that most of Ontario's Cave Swallow records have occurred during that week, with most records coming from 4 years: 1999, 2003, 2005, and 2008. Cave Swallows are now no longer a review-able species partly due to the epic year 2010 was for them (2010 Cave Swallow records weren't reviewed).

For the next graph, I excluded all Cave Swallow records.

The autumn records are normally distributed around the middle of November. There is a minor peak around the second week of October, though I doubt it is statistically significant. More than 20 records have been accepted by the OBRC (since 1997) every week from September 17 to December 2. While no weeks are as epic as in the spring, it goes to show that the fall is pretty consistent for rarities from now until early December. Get out there and find some rarities!

For the last two graphs, I only included species which I haven't seen yet this year. The first graph is with Cave Swallows included, and the second is without Cave Swallows.

The general shape of the graphs compared to the previous two are relatively the same, and reinforce that I should really be out there looking hard for the next 6 weeks or so. It is also important that I keep my schedule open during this time as there is a great possibility of potential year birds showing up left, right and centre for the next 6 weeks. From October 15 to the end of the year, there has been an average of 9.7 rarities that are also potential year birds every year. Of course some of these are duplicate species, and not all of them would be chase-able. It just shows that the potential is there for me to grab 5 or 6 more Code 4+ birds this autumn.

Anyways, just some "fun" things I was doing when I was bored!


  1. No surprise there are more OBRC reports in the Spring. Most birders are eager beavers in May looking for overshoots, reconnecting with nature and friends and enjoying the warm spring weather.
    How many are actually beating the bushes for the non vocal fall birds... Bet a hell of lots less.
    If you could get daily hours birded for all the birders in Ontario plotted per day. You would probably have an even more pronounced May bell curve somewhat similiar to your second graph.

    As for the dead week of FEB 19-25, that is no surprise. Most years, winter is still holding on and migration has not really started so most birders are at home inside. And what rare birds that wintered have already been reported.

    If you are still bored, have you plotted the number of OBRC species per week reported and the number of code 4 species/week that are reported.

    Or you could just join me tommorrow at Presquile and get the Purple sandpiper out of the way for the year and possibly another late fall Northumberland migrant.

    Brandon's "50 Days of Rare contest" hopefully will get more OBRC reportable birds found this year.



  2. Josh,

    Great analysis. As I published in OFO News for my Big Year at Point Pelee in 2005 (Volume 24, Number 1), the longest period (by far) when I failed to see a new species was the 22-day period from September 17 to October 9 inclusive. Very similar to your current situation!