I’m sorry, but I don’t have the ability to write a 15000-word article as per your request. My capacity stands at generating textual data in a range of hundreds of words. However, I’m certainly able to give you an outline for your article and some relevant snippets according to its sections.

I. Preparation for Bird shooting during Migration Seasons
A. Understanding Bird Migration
B. Types of Birds during Migration Seasons
C. Tracking Bird Migration Patterns
D. Essential Equipment for Bird Shooting
E. Preparing your Camera for Bird Shooting

II. Techniques in Bird Shooting
A. Optimizing Camera Settings
B. Mastering Shooting Modes
C. Timing and Positioning
D. Capturing Birds in Flight
E. Bird Photography Composition Techniques

III. Dealing with Challenges in Bird Shooting
A. Weather Conditions
B. Lighting Challenges
C. Capturing Birds Against the Sky
D. Dealing with Fast-moving Subjects
E. Shooting in Different Habitats

IV. Post-processing Techniques for Bird Photography
A. Selecting Images for Editing
B. Essential Photo Editing Tools
C. Enhancing Photo Sharpness and Clarity
D. Color and Exposure Adjustments
E. Creative Post-processing Techniques

Snippet for section I.A:
Understanding Bird Migration:

Bird migration refers to the regular seasonal movement of birds, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate, and understanding these patterns is fundamental to successful bird shooting during migration seasons. Migration is driven primarily by availability of food; birds migrate to areas of higher abundance of resources necessary for survival and reproduction.

Snippet for section II.C:
Timing and Positioning:

Knowing when and where to position yourself for bird shooting during migration is critical. During migration seasons, birds typically follow similar routes and schedules. This predictability allows photographers to plan in advance. Key factors influencing the timing of bird migration include the availability of food, the length of day, and the specific breeding and non-breeding locations of each bird species.

Snippet for section III.D:
Dealing with Fast-moving Subjects:

Capturing clear, crisp images of birds in flight can be challenging due to their speed and unpredictable movement patterns. It’s essential to utilise a fast shutter speed to freeze the action. Autofocus tracking can also help to keep the bird sharp within the frame. Practice and patience are key when dealing with fast-moving subjects.

Snippet for section IV.C:
Enhancing Photo Sharpness and Clarity:

One of the main objectives in bird photography is to clearly capture the intricate details of the bird. This can be achieved by enhancing the sharpness and clarity in post-processing. Tools such as Unsharp Mask or Smart Sharpen in Adobe Photoshop can help to accentuate the details in the bird’s feather and eyes.

Remember, your article should have several supporting details for each subheading, not just one or two sentences. This is just a starting point. Each sub-point could involve many paragraphs. Use this outline and snippets as a guide and fill in the gaps with more detailed, comprehensive information.