Cold weather doesn’t have to mean cold hands, but it often does - numb fingers stumble around the focus knob of binoculars, struggle to leaf through a field guide, and beg to be wrapped around a hot cup of coffee.
The first way to prevent cold hands is to not be cold anywhere - when the body begins to feel cold, it responds by reducing circulation to the extremities, and that’s bad news for the hands and feet. Being warm is a package deal. So wear the right layers, get a good hat and neck gaiter, and you are on the way to warm hands.
What you eat and drink is also important, and unfortunately, coffee is on the do NOT consume list. Coffee is a vaso-constrictor and as such reduces circulation to the extremities, exactly what you don’t need. However, you can and should ingest some other not-necessarily-good-for-you-otherwise foods: fats. Fatty foods like cheese, eggs, bacon, or peanut butter are very calorically dense foods, and calories keep you warm.
Obviously, to have warm hands you’re going to need some kind of glove or mitten. Mittens are warmer than gloves because your fingers work as a team to keep warm. But although some birders use mittens, I find they impair dexterity with optics too much, and have always preferred gloves.
From left to right, the line-up for warm hands. Insulated leather shooting gloves, ideal for all-around birding in cool to cold weather; insulated, Gore-tex lined gloves, for damp or rainy days; heavy, Gore-tex lined and Thinsulate insulated gloves for bitter cold, and disposable handwarmers, which can be inserted in any of the gloves for the bitterest of days.
My favorite birding gloves were actually designed as shooting gloves by a company called Bob Allen. Made of leather with an insulated lining, these keep hands warm down to upper 20’s F, and colder when I’m dealing with in-and-out-of-the-car birding.
If it’s damp or rainy, waterproof gloves are a must, so a glove with a Gore-tex liner and Thinsulate or other insulation is called for. I have two pairs of these, one with lightweight 50-gram insulation, and another with much heavier 150-gram insulation that are quite big and bulky, but warm. The latter gloves were also designed for shooting, and have a less-insulated index finger that makes it a bit easier to focus binoculars.
In extreme cold, disposable hand warmers are a final line of defense against cold hands. I usually place these inside my gloves, on the palm side so I can wrap my fingers around the hand warmer.
Handling cold binoculars or metal tripods will quickly chill hands. The tripod issue can be helped by wrapping the legs with foam insulation of the type used to insulate around water pipes, readily available at any home supply store. As far as binoculars, no one has come up with a binocular heater (yet), but a somewhat effective substitute is the dashboard of your car. Between stops, toss your bins on the dash and run the defroster. They won’t be frigid when you next get out, and if it’s been a bit of a drive, will feel quite toasty for a little while.