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Observed preference of Anna's hummingbirds for older feeder nectar over fresh


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I'm wondering if anyone else with a sciencey mind has noticed this preference, or has hypotheses about it. 

Here are my observations:

I have 2 identical feeders of the same age side by side on my balcony. I make my nectar from sucrose 1:4 with water in summer, and depending on how bad the weather gets in winter, I mix it 1:3 or rarely even 1:2. Most of my hummers appear to be the offspring of a lone male who practically lived at my feeder about 7 years ago when no one else had feeders in the area. Now there are many, but there are also other feeders.

I have noticed that when I wash and fill one feeder, the birds use the old one instead of the fresh. They sometimes fly up to the new one, approach a port, but apparently without tasting it, they leave and go to the other. They prefer the older feeder even if it only has a few teaspoon of nectar left in the tray.

I never leave food out long enough to become visibly spoiled, but in winter, a couple of weeks isn't unusual, sometimes longer. I imagine there is a small amount of alcohol. It doesn't seem evolutionary sound for hummers to be drawn to alcohol because that sensation of warmth (if there's enough to do that) is false. It would actually cause them to lose body heat.

 

I've experiemnted, and it seems they prefer old 1:4 nectar over fresh 1:3 nectar. If both feeders are changed at the same time, they don't seem to have a preference. If one feeder has fresh 1:3 nectar and the other gets fresh 1:4 nectar, they prefer the 1:3. If I switch the feeders around so the old nectar is where the new nectar was, they still find the old nectar. They will lick that feeder dry before starting on the newer feeder.

The only time I see them at the newer nectar when there is also older nectar is about 15 minutes before sunset when traffic is high, aggression is low, and the older feeder has several birds at it so the late comers have to use the fresher feeder.

My hypotheses:

The odor of spoilage attracts them

They are put off by the scent (or taste) of doshwashing liquid (although I rinse VERY well.

They form such strong fidelity to specific productive flowers that they won't abandon them until they stop producing (i.e., the old nectar is dependable, so they have no interest in a new source). But this doesn't seem evolutionary sound either because I would think it best to have many sources.

 

So, anyone else observed this, or have some ideas? It's fascinating to me.

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Most birds don’t really have a good sense of smell and rely more on vision than anything else. Hummingbirds feed on unscented flowers and feeders all the time, and are instead attracted to the colour. Which is why sometimes you can be wearing red and one will come check you out. There have been recent studies where they believe hummingbirds can smell certain insects and they tend to avoid feeders/flowers that have those scents, but there’s also been studies that show they have no preference between scented and unscented flowers. So I don’t think smell has anything to do with it (unless maybe whatever you wash the feeder with smells like an ant or something)
 

I believe sugar is more dense than water, so maybe overtime in the feeder, the liquid sugar settles on the bottom making it far more concentrated where they drink and thus more desirable? Or in a similar sense as the water evaporates, the solution becomes more concentrated?

I’m pretty sure nectar in flowers has the capacity to ferment as well, so I think it can assumed that hummingbirds would have at least some form of tolerance to alcohol. Though, other birds like robins and waxwings get drunk off of fermented berries all the time. It may affect them negatively in one way, but the benefits probably outweigh the costs in this scenario, especially in the winter. Alcohol induced food or not, they are eating which allows them to survive another day and they’re probably better off than a hummingbird that has no access to food at all. So it may not be the best option, but if it allows them to survive the winter and reproduce the following spring, it is not going to get selected against. 
 

There’s lots of studies and theories about patch dynamics that I won’t get into, but it’s often far more complicated than it seems. There’s lots of risk involved in having multiple sources. To have multiple sources, you have to spend time and energy finding them in the first place. Which can result in a lot of wasted energy and is risky in the sense that there may not even be any other sources available. Traveling over larger distances also increases the chances that you’ll run into a predator. Having many sources usually means (for certain species anyways) that you’ll have to spend far more time defending them which is a big energetic cost. And then there’s also the chance that you do not need to seek out any new sources in the first place because your current patch is sufficient enough so why bother. So staying at the same few resources is often far more safer and optimal for an organism up until the point that those resources stop being as productive to which it is then worth the risk to go find new ones. Of course, that probably doesn’t apply to your scenario as the feeders are in the same area. 

I’ve never experienced a preference for old vs new feeders with my hummingbirds, but I replace them at the same time every three days so can’t say I’ve given them a chance to choose!

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On 3/6/2022 at 2:44 PM, Dragonflyspit said:

I'm wondering if anyone else with a sciencey mind has noticed this preference, or has hypotheses about it. 

Here are my observations:

I have 2 identical feeders of the same age side by side on my balcony. I make my nectar from sucrose 1:4 with water in summer, and depending on how bad the weather gets in winter, I mix it 1:3 or rarely even 1:2. Most of my hummers appear to be the offspring of a lone male who practically lived at my feeder about 7 years ago when no one else had feeders in the area. Now there are many, but there are also other feeders.

I have noticed that when I wash and fill one feeder, the birds use the old one instead of the fresh. They sometimes fly up to the new one, approach a port, but apparently without tasting it, they leave and go to the other. They prefer the older feeder even if it only has a few teaspoon of nectar left in the tray.

I never leave food out long enough to become visibly spoiled, but in winter, a couple of weeks isn't unusual, sometimes longer. I imagine there is a small amount of alcohol. It doesn't seem evolutionary sound for hummers to be drawn to alcohol because that sensation of warmth (if there's enough to do that) is false. It would actually cause them to lose body heat.

 

I've experiemnted, and it seems they prefer old 1:4 nectar over fresh 1:3 nectar. If both feeders are changed at the same time, they don't seem to have a preference. If one feeder has fresh 1:3 nectar and the other gets fresh 1:4 nectar, they prefer the 1:3. If I switch the feeders around so the old nectar is where the new nectar was, they still find the old nectar. They will lick that feeder dry before starting on the newer feeder.

The only time I see them at the newer nectar when there is also older nectar is about 15 minutes before sunset when traffic is high, aggression is low, and the older feeder has several birds at it so the late comers have to use the fresher feeder.

My hypotheses:

The odor of spoilage attracts them

They are put off by the scent (or taste) of doshwashing liquid (although I rinse VERY well.

They form such strong fidelity to specific productive flowers that they won't abandon them until they stop producing (i.e., the old nectar is dependable, so they have no interest in a new source). But this doesn't seem evolutionary sound either because I would think it best to have many sources.

 

So, anyone else observed this, or have some ideas? It's fascinating to me.

Your hypothesis that the hummers would be more attracted to older (smelly) nectar makes perfect sense to me.  In the wild, the hummers are going to get used to making the best of the nectar that is available to them so if they find nectar sources with a reliable consistency, they will probably utilize it until it is gone or so rancid that it becomes unusable.  You see this in other animals too.  Especially scavenger type animals like buzzards and catfish. They go for the smelly stuff!  Ha ha! 

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