﻿A 
  Migration 
  of 
  Yellow 
  Butterflies 
  in 
  Trinidad. 
  83 
  

  

  Relation 
  of 
  Flight 
  to 
  Wind. 
  

   It 
  is 
  natural 
  that 
  the 
  result 
  just 
  obtained 
  would 
  be 
  affected 
  

   by 
  the 
  strength 
  of 
  the 
  wind 
  (at 
  this 
  particular 
  time 
  they 
  were 
  

   flying 
  with 
  a 
  hght 
  wind), 
  and 
  it 
  is 
  also 
  necessary 
  to 
  take 
  into 
  

   consideration 
  the 
  relation 
  between 
  the 
  direction 
  of 
  the 
  wind 
  

   and 
  that 
  of 
  the 
  migration. 
  

  

  Wind 
  records 
  are 
  kept 
  at 
  Port 
  of 
  Spain, 
  but 
  unfortunately 
  

   the 
  records 
  for 
  the 
  27th 
  of 
  September, 
  the 
  day 
  the 
  butter- 
  

   flies 
  were 
  timed, 
  were 
  sent 
  away 
  before 
  I 
  could 
  obtain 
  them. 
  

   The 
  average 
  wind 
  velocity 
  at 
  Port 
  of 
  Spain 
  between 
  9 
  a.m. 
  

   and 
  4 
  p.m. 
  from 
  the 
  1st 
  to 
  7th 
  October 
  was 
  8 
  miles 
  per 
  

   hour, 
  and 
  as 
  my 
  notes 
  record 
  that 
  the 
  wind 
  at 
  that 
  time 
  was 
  

   slight 
  it 
  was 
  probably 
  below 
  this 
  figure. 
  

  

  The 
  prevailing 
  wind 
  in 
  Trinidad 
  is 
  from 
  the 
  east, 
  and 
  as 
  

   this 
  migration 
  was 
  towards 
  the 
  west 
  it 
  might 
  be 
  thought 
  

   that 
  the 
  wind 
  determined 
  the 
  direction. 
  In 
  British 
  Guiana, 
  

   however, 
  for 
  Callidryas 
  euhide 
  it 
  was 
  found 
  that 
  the 
  usual 
  

   direction 
  was 
  across 
  the 
  wind, 
  and 
  there 
  are 
  enough 
  indi- 
  

   vidual 
  exceptions 
  in 
  the 
  present 
  case 
  to 
  leave 
  no 
  doubt 
  that 
  

   the 
  direction 
  of 
  the 
  wind, 
  although 
  contributory, 
  is 
  not 
  the 
  

   determining 
  factor 
  of 
  the 
  direction 
  of 
  flight. 
  

   The 
  following 
  cases 
  may 
  be 
  quoted 
  : 
  — 
  

   4.X.18. 
  Port 
  of 
  Spain— 
  no 
  wind, 
  flight 
  N.W. 
  (A. 
  Homber- 
  

  

  sley). 
  

   27.ix.18. 
  Guiaco— 
  wind 
  N.E., 
  flight 
  N.W. 
  (J. 
  B. 
  

  

  Rorer). 
  

   12.x. 
  18. 
  At 
  sea 
  off 
  Gasparee 
  — 
  " 
  endeavouring 
  to 
  fly 
  

   west, 
  but 
  owing 
  to 
  strong 
  N.W. 
  wind 
  (15-20 
  m.p.h.) 
  

   actual 
  course 
  was 
  between 
  S. 
  and 
  S.S.W." 
  (C. 
  P. 
  

   Milne). 
  

   1.x. 
  18. 
  San 
  Fernando 
  — 
  flying 
  N. 
  against 
  the 
  wind 
  (P. 
  

  

  Crato). 
  

   5.X.18. 
  Macqueripe 
  — 
  ■" 
  flew 
  seaward 
  and 
  were 
  blown 
  

   back 
  by 
  the 
  force 
  of 
  the 
  wind 
  " 
  (local 
  newspaper). 
  

  

  Mr. 
  J. 
  A. 
  Bullbrook 
  further 
  points 
  out 
  that 
  the 
  wind 
  can- 
  

   not 
  be 
  the 
  conclusive 
  factor 
  in 
  the 
  direction 
  of 
  flight, 
  as 
  

   when 
  flying 
  in 
  hilly 
  country 
  they 
  continue 
  in 
  the 
  same 
  direc- 
  

   tion 
  down 
  the 
  shaded 
  leeward 
  side 
  of 
  a 
  hill 
  as 
  they 
  were 
  

   flying 
  when 
  ascending 
  the 
  windward 
  side, 
  and 
  that 
  on 
  both 
  

   sides 
  they 
  keep 
  about 
  the 
  same 
  distance 
  from 
  the 
  tops 
  of 
  the 
  

   trees. 
  

  

  I 
  can 
  from 
  my 
  own 
  observation 
  confirm 
  this 
  interesting 
  

   note. 
  

  

  