﻿Mr. 
  C. 
  B. 
  Williams 
  on 
  Migration 
  of 
  Yellow 
  Butterflies. 
  77 
  

  

  rising 
  above 
  a 
  few 
  hundred 
  feet. 
  There 
  is 
  no 
  accurate 
  map 
  

   of 
  the 
  contours 
  of 
  the 
  Island, 
  but 
  the 
  first 
  small 
  map 
  on 
  

   Fig. 
  I 
  shows 
  approximately 
  the 
  positions 
  of 
  these 
  three 
  

   ranges. 
  

  

  The 
  chmate 
  of 
  the 
  Island 
  is 
  tropical, 
  average 
  day 
  tem- 
  

   perature 
  above 
  80°, 
  and 
  the 
  year 
  is 
  divided 
  into 
  one 
  wet 
  

   and 
  one 
  dry 
  season. 
  In 
  general 
  the 
  dry 
  season 
  lasts 
  from 
  

   the 
  middle 
  of 
  January 
  to 
  the 
  middle 
  of 
  May, 
  and 
  the 
  wet 
  

   season 
  from 
  June 
  to 
  December. 
  

  

  The 
  average 
  yearly 
  rainfall 
  is 
  about 
  65 
  inches, 
  of 
  which 
  

   August 
  averages 
  9*8 
  inches 
  and 
  September 
  7*2 
  inches. 
  

   There 
  is 
  occasionally 
  a 
  spell 
  of 
  dry 
  weather 
  about 
  Sep- 
  

   tember, 
  forming 
  what 
  is 
  known 
  as 
  the 
  " 
  Indian 
  summer," 
  

   and 
  it 
  should 
  be 
  noted 
  that 
  in 
  the 
  present 
  year 
  (1918) 
  

   this 
  has 
  been 
  particularly 
  well 
  marked. 
  During 
  the 
  six 
  

   weeks 
  previous 
  to 
  the 
  migration 
  to 
  be 
  described 
  below 
  the 
  

   weather 
  had 
  been 
  unusually 
  dry, 
  many 
  locahties 
  recording 
  

   less 
  than 
  three 
  inches 
  for 
  September, 
  and 
  in 
  the 
  extreme 
  

   south-west 
  scarcely 
  any 
  rain 
  fell 
  for 
  six 
  weeks. 
  

  

  The 
  prevaihng 
  wind 
  is 
  the 
  east 
  or 
  north-easterly 
  trade 
  

   wind. 
  

  

  Methods 
  of 
  Recording. 
  

  

  It 
  has 
  been 
  thought 
  unnecessary 
  to 
  give 
  in 
  detail 
  the 
  

   numerous 
  records 
  which 
  were 
  collected. 
  Instead 
  they 
  have 
  

   been 
  transferred 
  to 
  the 
  accompanying 
  series 
  of 
  maps 
  by 
  

   a 
  system 
  of 
  arrows, 
  crosses, 
  and 
  circles 
  representing, 
  

   respectively, 
  movements, 
  abundance, 
  or 
  absence 
  of 
  the 
  

   butterflies. 
  

  

  By 
  referring 
  to 
  the 
  maps 
  for 
  the 
  19th 
  September 
  to 
  the 
  

   12th 
  October 
  the 
  course 
  of 
  the 
  migration 
  day 
  by 
  day 
  can 
  

   be 
  easily 
  followed. 
  On 
  the 
  larger 
  map 
  (PI. 
  X) 
  all 
  the 
  

   records 
  have 
  been 
  combined, 
  and 
  in 
  addition 
  two 
  or 
  three 
  

   added 
  which 
  do 
  not 
  appear 
  on 
  the 
  first 
  series 
  ; 
  these 
  being 
  

   records 
  in 
  which 
  the 
  locality 
  and 
  direction 
  was 
  given 
  but 
  

   the 
  exact 
  date 
  could 
  not 
  be 
  ascertained. 
  

  

  The 
  signs 
  used 
  on 
  the 
  maps 
  are 
  as 
  follows 
  :— 
  

  

  (1) 
  Arrow 
  with 
  one 
  head 
  : 
  Very 
  slight 
  migration, 
  one 
  or 
  

   two 
  per 
  minute 
  within 
  sight 
  of 
  the 
  observer. 
  Only 
  notice- 
  

   able 
  with 
  special 
  care. 
  Probably 
  not 
  recorded 
  except 
  by 
  

   skilled 
  observer. 
  

  

  (2) 
  Arrow 
  with 
  two 
  heads 
  : 
  Three 
  or 
  four 
  butterflies 
  per 
  

   minute 
  passing 
  across 
  one 
  hundred 
  yards 
  fine 
  ; 
  easily 
  

   noticeable 
  to 
  a 
  skilled 
  observer, 
  and 
  probably 
  seen 
  by 
  any 
  

  

  