I've attached photos of the buds and bark of a tree I came across on a walk today. I'm completely baffled as to what it is. My field guide key was of no help. The tree was about 15cm in diameter. The buds were on stalks (varying in length) as the photo illustrates. The trunk was grey (almost silver (although it was a bright day!)
Probably wild cherry (also called gean or mazzard) (Prunus avium), especially if it was growing wild. However, there are many similar-looking culitvated cherries with which it is confusable. If you pass it again, make a note of the colour of the flowers and whether they are single or double (in the horticultural sense). Gean flowers are single and white. There are other characters to look for, as well, including the fruit later in the season.
The tree called 'bird cherry' is a different species, Prunus padus. Yes, you would think 'avium' would suggest 'bird', and Prunus avium is sometimes called bird cherry, but that is not really correct.
Tip 1: When trying to identify a deciduous tree in winter, look at the leaves on the ground. Yes, there may be a mixture, coming from various nearby trees, but you should be able to see which are the most common, which may therefore be from the closest tree. The colour will not help you, but the shape and various details (toothing, veining, size) will.
Tip 2: Species of Prunus have leaves that are distinctive in having a pair of brown/red lumps (extrafloral nectaries) towards the top of the leaf stalk. That is shown in a photo on the page addressed above.
Tip 3: That sort of bark - with large areas that are so smooth they look almost clingfilmed, points to cherry (Prunus, many species), birch (Betula, many species) or paperbark maple (Acer griseum, one species). That is not to say all species in those genera have smooth or partly-smooth bark, but there are many species that do.
Many other species have somewhat smooth bark (eg. beech, hawthorn, especially when young); that is different.