﻿366 
  Mr. 
  F. 
  A. 
  Lucas 
  on 
  

  

  In 
  reply 
  to 
  the 
  query 
  '' 
  How 
  is 
  it 
  that 
  Humming-birds 
  

   are 
  restricted 
  to 
  America 
  ? 
  "' 
  I 
  would 
  say, 
  for 
  much 
  the 
  same 
  

   reason 
  that 
  torpedo-boats 
  do 
  not 
  cross 
  the 
  Atlantic 
  — 
  lack 
  of 
  

   power 
  and 
  fuel-capacity. 
  The 
  Humming-birds, 
  from 
  their 
  

   great 
  local 
  multiplicity 
  of 
  species, 
  probably 
  originated 
  in 
  

   South 
  America 
  and 
  spread 
  northward 
  *, 
  Since 
  their 
  excessive 
  

   activity 
  calls 
  for 
  great 
  expenditure 
  of 
  muscular 
  tissue, 
  they 
  

   need 
  a 
  liberal 
  supply 
  of 
  food, 
  and 
  this 
  food 
  consists 
  prin- 
  

   cipally 
  of 
  minute 
  insects 
  which 
  are 
  to 
  be 
  had 
  only 
  in 
  proper 
  

   localities. 
  Migration 
  by 
  way 
  of 
  the 
  north 
  is 
  out 
  of 
  the 
  

   question 
  ; 
  there 
  are 
  no 
  way-stations 
  on 
  the 
  ocean 
  ferry, 
  and 
  

   even 
  were 
  the 
  Humming-bird 
  sufficiently 
  powerful 
  in 
  flight 
  

   to 
  cross, 
  it 
  would 
  starve 
  to 
  death 
  on 
  the 
  way. 
  

  

  We 
  are 
  told 
  that, 
  as 
  to 
  plumage. 
  Swifts 
  have 
  no 
  sexual 
  

   colour-distinctions, 
  nor 
  plumes, 
  nor 
  ornamental 
  feathers, 
  while 
  

   Humming-birds 
  have 
  all 
  three. 
  Now 
  in 
  Chcetura 
  rutila 
  and 
  

   C. 
  rufitorques, 
  and 
  in 
  all 
  the 
  species 
  of 
  Macropteryx, 
  the 
  males 
  

   and 
  females 
  are 
  different, 
  while 
  in 
  about 
  one-third 
  of 
  the 
  

   known 
  species 
  of 
  Humming-birds 
  the 
  sexes 
  are 
  robed 
  alike. 
  

   The 
  long 
  tail-feathers 
  of 
  some 
  of 
  the 
  Swifts 
  might 
  well 
  be 
  

   considered 
  ornamental, 
  and 
  all 
  species 
  of 
  Macropteryx, 
  

   notably 
  M. 
  mystacea, 
  have 
  local 
  plumes 
  or 
  crests. 
  

  

  As 
  to 
  pterylosis, 
  the 
  Humming-bird 
  has 
  a 
  spindle-shaped 
  

   apterium 
  on 
  the 
  crown, 
  and 
  the 
  Swift 
  an 
  inverted, 
  crescent- 
  

  

  * 
  Birds 
  of 
  restricted 
  range 
  seem 
  to 
  have 
  a 
  tendency 
  to 
  split 
  up 
  into 
  

   species 
  and 
  subspecies, 
  as 
  in 
  the 
  well-known 
  case 
  of 
  the 
  birds 
  of 
  the 
  

   Galapagos 
  Islands. 
  In 
  the 
  American 
  genus 
  Harporhynchus 
  one 
  species, 
  

   H. 
  rufus, 
  is 
  migratory 
  and 
  widespread, 
  the 
  eight 
  other 
  species 
  and 
  sub- 
  

   species 
  are 
  non-migratory 
  and 
  of 
  restricted 
  and 
  contiguous 
  habitats, 
  and 
  

   we 
  see 
  the 
  same 
  thing 
  repeated 
  in 
  the 
  genus 
  Pipilo. 
  There 
  would 
  seem 
  

   to 
  be 
  good 
  reason 
  for 
  this. 
  As 
  a 
  non-migratory 
  bird 
  spread 
  outward 
  

   from 
  its 
  original 
  centre, 
  it 
  would 
  meet 
  in 
  different 
  localities 
  with 
  

   different 
  conditions 
  of 
  food, 
  climate, 
  and 
  physical 
  surroundings. 
  Genera- 
  

   tion 
  after 
  generation 
  would 
  be 
  subjected 
  to 
  the 
  same 
  conditions 
  as 
  their 
  

   ancestors, 
  and 
  any 
  forces 
  that 
  might 
  cause 
  variation 
  would 
  be 
  continuously 
  

   at 
  work, 
  while 
  any 
  variation, 
  whether 
  arising 
  from 
  external 
  or 
  internal 
  

   causes, 
  would 
  stand 
  a 
  better 
  chance 
  of 
  pei-petuation 
  by 
  in-breeding 
  among 
  

   birds 
  living 
  and 
  breeding 
  in 
  one 
  locality 
  than 
  among 
  migratory 
  species, 
  

   where 
  the 
  chance 
  of 
  destruction 
  or 
  separation 
  of 
  individuals 
  during 
  their 
  

   journeys 
  would 
  naturally 
  be 
  greater. 
  

  

  