I truly appreciate Brandon's concerns and that he was worried enough that he left a comment. I created a very detailed response that I've decided to share as a new post because even though he's the only one who has written a message to me about his concerns, I'm certain he's not the only person who has had them.
I do appreciate your concern. I too first worried that scent would prove to be stressful to a mother bird. After quite a bit of research I learned that that just isn't true. Mother birds will eagerly take back nests and baby birds that have been touched by humans because, with the exception of vultures, most birds do not have a highly developed sense of smell.
MYTHS AND MISCONCEPTIONS
Fact or Fiction?: Birds (and Other Critters) Abandon Their Young at the Slightest Human Touch
What can birds smell? Sniffing out the facts
But I haven't just read it. Years ago I found a dove's nest on the ground and replaced it to the nook between a rain gutter and the side of the garage using wire to hold it in place so it wouldn't fall again. The doves used it again and again over the following years.
With nests 7' from the ground you can see the chicks even without a ladder.
The birds in my yard are used to my presence. Last year I observed long enough to know that the mother leaves the nest several times each hour to go find food to bring back to feed the babies so it's simply a matter of waiting for her to leave and knowing each time she does I have at least a fifteen minute window to take pictures of the babies until she comes back. When she does she's there for just seconds to feed them before taking off again.
The babies (for their part) tolerate all yard activity quite well. The lawn mower each week, our neighbor's gardner's leaf blower, and even my dog barking at things along the fence below their nest are no cause of alarm to them. Last year we had our house painted and it wasn't until the morning before the painters arrival that I noticed the babies had hatched. The painters used a lot of care not to damage or disturb the nest and the mother acclimated to their presence just fine. I think the birds know no harm will come to them from the people who appear in our yard or they wouldn't continue nesting here year after year.
As for myself losing my balance and damaging their nest here are two things I can tell you to try to reassure you:
1. Usually I'm at least 5-15 feet away from the nest but it seems like I'm closer because of the powerful telephoto lens.
2. Using a ladder when I do use my macro lens doesn't mean I'm teetering atop it. I'm only one to two steps up on our six foot ladder because the birds build their nests surprisingly close to the ground. This means I can use the remaining steps to lean against, bracing myself and creating far more stability than what would be possible standing atop a chair. Our neighbors across the street have a bird that nests each year in their rose bushes. In these instances falling from a precarious height while taking pictures isn't something one has to worry about when photographing Anna's Hummingbirds.
I hope this reassures you at least a bit that the birds are perfectly safe from human harm.
(End of response)
As an example, here's the close up I posted yesterday before and after cropping. The ladder was set up 4 feet from the nest, the mother nowhere in sight.
Here's another original photo beside the cropped close-up I used in yesterday's post. It illustrates I wasn't hovering above the babies when I got the close-up of their green back feathers.
Had I somehow managed to fall from the single foot I was elevated above ground level the only injury would have been most likely to my camera. The babies were safe from harm.