Since Dan got his Master banding permit, we’ve put up a few nets to get a start on some of our planned projects. I mentioned the owl monitoring already in an earlier post. This morning we opened a net that we set up near our feeders. Dan goes into more detail on the purpose of the project, but essentially it’s to learn more about the local winter ecology of our resident birds – things like population sizes and demographics, survivorship over the winter, and general health of individuals (hopefully if we’re supplementing their diet with feed they’ll all be in good health, but it may lend some insight into the food resource abundance outside of the feeders).
There’s a lot of information that’s either extremely difficult or impossible to obtain without using banding studies. Two such pieces of info were evident from our efforts this morning. The first was that there were a lot more Blue Jays visiting our feeders than we’d first thought. By visual counts, simply watching the feeders and seeing who was around, we guessed there were perhaps 5 or 6 coming for seed. This morning, however, we caught no fewer than 8 separate individuals in the net, and later on, once we’d closed the net for the day, saw an additional 3 together at the feeder who had no bands, making a minimum of 11. We observed some of the banded individuals coming to the feeder again a short while later. Free food is hard to pass up! Evidently they weren’t too put off by the quick banding process.
The second thing we learned is that there’s an unusual proportion of adults to young birds among them. In an average fall, at an average banding location, one might expect to capture about 80-90% hatch-year (HY) birds – that is, birds that were hatched in this calendar year. The remaining 10-20% are after-hatch-years (AHY) – the adults who were parents this calendar year. Among our 8 Blue Jays captured this morning, a whopping 6 – 75% – were adults. This could mean either it was an exceptionally poor breeding year for Blue Jays in our woods and they didn’t raise many offspring, or the offspring have all dispersed or flown south, leaving just the adults to spend the winter here. It’s hard to know the reason for sure, although seeing what the proportions are come spring (after any migrants have presumably returned) will help to answer the question.
You can tell the difference between the age classes of Blue Jays fairly easily. HY birds still have many of their “baby feathers”, that is, the set of feathers that they grew in while they were in the nest. They grow these feathers very quickly, because they want to limit the amount of time that they’re flightless and vulnerable to predation. However, because they grow them in all at once, and feathers are very energetically costly to grow, these “baby feathers” are of very poor quality. They’re generally rather coarse and dull, and will fade and wear down rapidly. Most songbird species have a pattern of moult whereby the HY birds will replace a portion of their feathers before the winter to see them through until their next moult (for some birds, this will be spring, but for many others they’ll have to wait until next fall). You can examine the feathers of a bird’s wing to see if it’s got any “baby feathers” – and most species have a very specific replacement pattern so it’s easy to know what to look for.
In the case of Blue Jays, the characteristic feathers are these small, outer feathers mid-way up the wing. They’re the little feathers that cover the sheathes of the long primary feathers (appropriately called the primary coverts), and the feather that comes from the thumb (the alula). In the above photo, you can see the left-hand bird, the AHY or adult, has very distinct barring to these outer feathers, and the colour is approximately the same as the larger neighbouring white-tipped feathers (the greater coverts, which cover the sheaths of the long inner secondary feathers). The right-hand bird, the HY or youngster, has relatively unmarked outer feathers which are a duller colour than the rich blues of the white-tipped greater coverts.
I love Blue Jays’ wings, the blue colour in them is simply surreal. While most feather colours are created through various pigments, blue and green different. Like the sky, blue is created through the refraction of light, not the absorption of it. A red feather will still look red when lit from underneath, but a blue feather loses all of its colour – check out this page for some neat photos demonstrating this. Likewise, if you grind up a red feather, you have a pile of red dust, but grinding up a blue feather does not produce blue dust (it will more likely be brownish or grayish).
The exact light-scattering mechanism employed in these blue feathers has traditionally been assumed to be similar to what happens in the sky – the light hits the microscopic structures and then scatters in all directions, with just the blue coming back to your eye (so why don’t you see red or orange when viewed at a sharp angle, like sunsets, you ask? Good question, and I don’t know the answer.) A paper published in 1998 argued that the blue was created through a different scattering method, called interference or coherent scattering, whereby the light wavelengths break up and then come back together again, and the way they meet up again all the colours cancel themselves out except for the blue.
Whichever it is, the end result is that it’s a colour produced through structure, not pigment. And it’s pretty amazing. Can you believe so many people simply look past these guys, desensitized because they’re common?