Drawing birds in flight can be challenging. It helps to develop an understanding of the way the wings foreshorten. If you make a cardboard model of a soaring bird, you can turn it to any angle and watch the way that its wings change shape. Practice making sketches of the models from all angles. You will quickly develop an intuitive understanding of how to draw birds in flight. In the Laws Guide to Drawing Birds I give the blueprints to make two models, one a gull, the other a hawk. The different wing shapes of these birds allow you to discover how the angles and proportions of the wings change on bent vs. straight wings and pointed wing tips vs. broad fingered primaries.
To try it yourself, download the paper model blueprints (follow the link and click on “make a flight model”), print it out on cardstock paper (you could also print onto regular paper and glue it to sheet of cardstock), cut the birds out and fold their wings along the red dashed lines. The folds in the gull wing all fold down, the wing tips of the hawk fold up. Put a drop of glue on the inside of the head to hold it shut. Now close one eye (to avoid the confusion that comes from binocular vision) and turn the bird in your hands. You will be surprised how much you can learn from studying and drawing from these models.