There comes a time in every nestling’s life when they have to make a choice: stay in the nest, where it’s warm and mom and dad are there and there’s always breakfast and love and you can sleep all day… or venture forth into the scary, unknown fields and forests of possibly-murderous creatures with only your tiny, feathered self to rely on.
We all know it well.
But actually, nestlings are safer out of the nest than they are in it. Because if you think about it, a nest full of helpless baby birds is to a predator what a basket full of unguarded muffins is to me – the best thing in the world to find. Which is why nestlings develop at an astonishing rate, and why parent birds work so tirelessly to get them fed, grown, and out of there.
And so, all the little spotted American Robins, fluffy Song Sparrows, and extra-downy Downy Woodpeckers are taking a leap of faith (literally) and leaving their nests to test out their new wings, their awkwardly-large feet, and their parents’ patience. We had many such first-year birds in the nets for our fourth banding session.
And not only did we have all those youngins, we also had four new species.
Here are the totals:
Among the new species to be banded were Brown-headed Cowbird, Northern Mockingbird, Blue Jay, and Downy Woodpecker.
It was quite an exciting day, with all those new faces!!
Here are some photo highlights:
Cowbirds are the smallest members of the blackbird family (Icteridae), and of all bird species, their reproductive strategy might easily be considered the most evolutionarily advanced… or the most lazy. Female Cowbirds put all of their energy toward producing eggs (sometimes more than three dozen per season – I mean really, you would think they were chickens!!) which they lay in the nests of other species, earning them the name “brood parasites.”
This strategy allows them to save the energy that would have been allocated toward nest building, incubating, brooding, and feeding their nestlings, and also keeps them from the danger of vulnerably sitting on a nest. They can reproduce more, with less risk and resource use, than pretty much any other songbird. And so, one pair of Cowbirds is replaced by 1.2 pairs each year, which means that their population could double in less than a decade.
That is bad news for the many birds that fall victim to their parasitism. Those species’ eggs are often damaged by the female Cowbird (on purpose… can you imagine such a travesty?!), or are kicked out of the nest completely. The host species’ nestlings are also typically smaller and cannot compete with the larger Cowbird nestling(s) for resources, so they often don’t develop well and can starve. In some cases, the host species will recognize a foreign egg or nestling, and either kick it out or simply neglect it. But sadly, that’s not always how it goes.
We’ve been hearing Common Yellowthroats singing like crazy at Crossways, but they are sneaky, and this was only third one to be caught. If you look closely, you’ll notice a few ticks attached to him; it’s not uncommon for birds to have such ‘ectoparasites,’ especially those that tend to forage and nest lower in the understory.
Understanding how avian populations are affected by ticks, and whether or not they may contribute to the spread of tick-borne illnesses (including Lyme disease), is a pretty popular topic of field research, and has been for several years. The most common tick to target birds is not the deer tick, however, but the bird tick, Ixodes brunneus (another fine example of putting a lot of thought into naming things… not).
The bird tick can transmit what is known as ‘avian tick paralysism’ by introducing a chemical through the saliva, which causes paralysis to spread from the bird’s feet up. Of course, they cannot long survive in the wild once it progresses. Fortunately though, bird ticks are primarily found along the coast, and the disease doesn’t seem to be a considerable problem in our area (as far as we know, that is).
Here’s a close-up of the Mockingbird’s eye, indicating the nictitating membrane because it’s super weird and I want to tell you all about it.
The nictitating membrane is a strange and magical thing. Effectively a third, translucent eyelid, it slides horizontally across the bird’s eye (rather than up or down), and serves many purposes.
It provides extra protection to the bird’s eye – particularly useful for birds that forage under water (built in goggles!!), and for lack of a better way to put it… for birds who forage with their faces in carcasses (you know, like those creepy roadside turkey vultures). It also moisturizes the eye each time it glides over the eyeball, which is great for birds of prey that fly at very fast speeds, high up, where winds are stronger and more drying.
Since it’s clear, the birds are still able to see while getting all of those benefits. When you spend a lot of time flying up to 60 miles per hour toward dense objects (trees, buildings… people) and have to use your eyes to spot caterpillars and flies extremely far away, while remaining constantly alert and aware of your surroundings because EVERYTHING WANTS TO EAT YOU, it is important to be able to see at all times.
And while birds are admittedly less-susceptible to eye injuries than other species which have nictitating membranes (snakes, lizards, voles and other creatures that burrow and can easily get dust and dirt in their eyes), they are perhaps more negatively affected by any injury that does occur, since they depend so heavily on sight.
So it’s good that they have them.
There are two kinds of ‘bars’ which can be found on feathers: fault bars and growth bars.
Growth bars occur normally in growing birds, and are light and dark bands that stretch across a feather. The dark bands are grown during the day, when the bird’s metabolism is higher (and therefore more melanin is being produced), while the light bands are grown during the night. Together, the light and dark bands represent 24 hours of feather growth. These bands don’t impact the feather’s structural integrity, whereas fault bars do…
Fault bars are translucent, and can go partly or fully across the feather shaft. They represent the occurrence of some kind of environmental or physical stress, be it malnutrition, predator escape, etc., that occurred in a particular moment in time when that feathers was being grown (when the bird had to devote energy to something other than the feather’s growth, essentially). Since young birds are devoting energy toward physical growth, they produce fault bars more easily than adults. Eventually, fault bars can lead to complete feather breakage.
Birds in fragmented forests produce more fault bars than those in a healthy forest, due to the amount of stress that occurs when good spots of cover are few and far between. Some have even suggested that a high occurance of fault bars in wild birds in a given habitat signals poor environmental conditions, and can therefore alert conservationists to threatened ecosystems.
Not all hatch-year birds have major differences in plumage from their adult counterparts, but some do. Like American Robins.
This bird stumped me at first. Woodpeckers are a little unusual in that they can be aged more specifically than many species; as opposed to simply saying “After Second Year” for an adult, you can say “After Third Year,” and so on. Hatch Year and After Second Year birds also have some overlapping characteristics, so when I first looked at this bird, I called it an ASY.
But then later, when I thought about it more in the wee hours of the night, I realized I hadn’t remembered to check its eye color… and that maybe its undertail coverts were a little too downy and its tail was a little too pointy for it to be an adult…
So I sent photos to a fellow MAPS bander, who is operating a station in western PA, for advice (and reassurance), and she helped me confirm it as an HY (thanks, Gigi!!).
Alright friends, that’s it for day 4 highlights. 🙂
We’ve had a couple more sessions since, so come back to visit again soon!