In Part 1 I briefly introduced the species accumulation curve as a means of comparison of rates of discovery between different groups. Here, I wanted to parse apart any broad-scale patterns in the bird data. I started by splitting the birds into their two broadest groupings - passerines (5927 species) and non-passerines (4100 species) - and then I split passerines again into two more broad classes - oscines (4668 species) and suboscines (1259 species). These new species accumulation curves are plotted against the overall bird curve (in black):
(click to enlarge)
The non-passerine curve falls generally to the left of the passerines and birds overall, indicating that non-passerines were generally described earlier than passerines and fewer non-passerines have remained undescribed until recently. The passerine, oscine, and suboscine curves are generally similar in slope and position, although suboscines lag in the last 100 years or so. The suboscine curve is also the only one with a noticeable uptick - a bunch of new species described - in the last few decades.
Those who know me when I get into projects like this know I like to take things to ridiculous excess. In this case, I decided to investigate family-level patterns of description. To get fairly smooth accumulation curves requires a fairly large number of taxa, so I picked the bird families recognized by Birdlife that contain more than 150 species. These twenty families are:
And their species accumulation curves, plotted against the all-bird curve in black:
I don't expect anyone to actually tease apart that rainbow coalition of squiggles in detail, especially because they form such a tight column of similarly-sloped curves. That in itself is a pretty neat result - the family-level differences aren't as noticeable as I thought they would be, and teasing them apart in detail is fairly pointless. There are, however, two curves that stand apart from the rest.
On the far left in pale blue is Anatidae. 50% of the currently known ducks were described by 1800, decades before any other family, and 90% were described by 1870. Ducks are big, obvious birds with common interaction with humans (in the form of hunting) and often bold, distinct male plumages in each species. It is thus not surprising that ducks were described comparatively early in history and very few new species have been described in the last 100 years.
In contrast, on the right side of the curves, the pale reddish curve for Strigidae falls below the others in the last 100 years or so. The slope is pretty similar to the other curves for this time period, so I don't think the overall rate of discovery in owls is much lower. Instead, the curve is displaced lower by the flush of new species described in the last few decades - remember in my last post that owls had the highest number of new species described of any family since 1942.
That's all I have for now - have fun staring at those colorful squiggles.