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!