Eight persons — A, B, C, D, E, F, G and H were studying about different birds in different months of the same year, viz. January, March, May, June, July, October, November and December, but not necessarily in the same order. Each of them is studying about different birds — Kingfisher, Toucans, Penguin, Ostrich, Woodpecker, Loon, Sparrow and Peacock.

G is studying in the month having odd number of days. Either two persons were studying before G or after G. Two persons were studying between G and the one who is studying about loon. H was studying three persons after the person who is studying about ostrich and four months before A. Three persons were studying between A and the one who is studying about Woodpecker. B is studying about Sparrow two persons before F. F is studying before E. The one who is studying about Penguin is studying immediately after the one studying about Kingfisher. Two persons were studying between the ones studying about Kingfisher and Peacock. D is not the first one to study.

How many persons were studying between D and the one studying about Kingfisher?

To solve this puzzle, let us list the months in chronological order along with the number of days in each month:

1. January (31 days)
2. March (31 days)
3. May (31 days)
4. June (30 days)
5. July (31 days)
6. October (31 days)
7. November (30 days)
8. December (31 days)

Now, let's analyze the clues step-by-step to place the persons (A, B, C, D, E, F, G, H) and their respective birds:

• G's position: G is studying in a month with an odd number of days (31 days). Either two persons study before G or two persons study after G.
  This means G is either the 3rd person (May) or the 6th person (October).
• Loon's position: Two persons study between G and the one studying about Loon.
  If G is 3rd (May), the one studying about Loon must be 6th (October).
  If G is 6th (October), the one studying about Loon must be 3rd (May).
• H, A, and Ostrich: H is studying three persons after the person studying about Ostrich (so if Ostrich is at position $x$, H is at $x+3$). Also, H is studying four months before A.
  Looking at the calendar months, the possible pairs that are exactly 4 months apart are:
  • January (1st month) to May (5th month)
  • March (3rd month) to July (7th month)
  • June (6th month) to October (10th month)
  • July (7th month) to November (11th month)
  Since H is 3 persons after Ostrich, H cannot be in January or March. Thus, H must be in June (4th person) or July (5th person).
  If H is in June (4th person, month 6), then A is in October (6th person, month 10). This aligns perfectly because:
  • Ostrich must be the 1st person (January).
  • Since A is the 6th person (October), G must be the 3rd person (May).
  • The one studying about Loon is the 6th person, which is A.
• Woodpecker's position: Three persons study between A (6th person) and Woodpecker.
  Thus, Woodpecker must be the 2nd person (March).
• B, F, and E: B is studying about Sparrow two persons before F (so B is at position $y$ and F is at $y+2$). F is studying before E.
  The available positions for B and F are 5 (July) and 7 (November). Thus:
  • B is the 5th person (July) studying about Sparrow.
  • F is the 7th person (November).
  • Since F is before E, E must be the 8th person (December).
• D and C: D is not the first one to study.
  Since the 1st position (January) and 2nd position (March) are vacant for persons, D must be the 2nd person (March) and C must be the 1st person (January).
• Remaining Birds:
  • The one studying about Penguin is studying immediately after Kingfisher.
  • Two persons study between the ones studying about Kingfisher and Peacock.
  This fits if Kingfisher is the 7th person (F), Penguin is the 8th person (E), and Peacock is the 4th person (H).
  Consequently, G (3rd person) studies about Toucans.

The final chronological arrangement is as follows:

We need to find the number of persons studying between D and the one studying about Kingfisher (F):

D is studying in March (2nd person) and Kingfisher (F) is studying in November (7th person).

The persons studying between them are G, H, B, and A.

Therefore, there are exactly Four persons studying between D and the one studying about Kingfisher.