Brown sugar contains molasses (that's why it's brown)
and will ferment quickly in your feeder. It is also more
prone to growing a fungus that can kill hummingbirds (which
is a reason why you shouldn't use honey, either).

I suspect that if you fill one feeder with brown sugar solution
and another with pure cane sugar (not cheap generic sure made
from beets which has a higher glucose and fructose content). You
will find that they prefer the white sugar.

One of many sites with information on NOT using brown sugar is
at http://www.hummingbirds.net/feeders.html

Michael Hobbs wrote:
>
> Tweets - I've tried it, and they like it, but I don't know if its a good
> thing.
>
> The other day, after noticing a couple of hummers in the neighbor's yard, I
> put up my hummingbird feeder. Previously, we had had no success feeding
> hummers in our yard, and I'd given up. When I went to mix up some solution,
> I saw the brown sugar in the cupboard and thought "why not?". So I mixed up
> 1 part brown sugar to 4 parts water and filled the feeder. And the hummers
> have been coming, including the first ANNA'S I've ever seen in our yard.
>
> I cannot find reference to whether brown sugar is good or bad for
> hummingbirds. All the published recipes I can find call for ordinary white
> sugar, but they don't specifically say not to use brown sugar. Is brown
> sugar bad for hummingbirds, or is it simply not worth the extra expense? It
> would seem possible that there would be trace minerals and maybe even
> vitamins in brown sugar that would not be in white sugar. But possibly
> brown sugar might spoil faster?
>
> Any clues?
>
> == Michael Hobbs
> == Kirkland, WA
> == hummer at isomedia.com

--
Mike Patterson
Astoria, OR
celata at pacifier.com

A child who becomes acquainted with the birds about him
hears every sound and puzzles out its meaning with a cleverness
that amazes those with ears who hear not.

-Neltje Blanchan

http://www.pacifier.com/~mpatters/bird/bird.html