﻿374 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  change 
  in 
  the 
  rhythms 
  of 
  the 
  reproductive 
  activities, 
  leading 
  to 
  a 
  

   change 
  of 
  instincts 
  * 
  * 
  *. 
  As 
  to 
  the 
  'why 
  of 
  this 
  problem' 
  

   that 
  is, 
  why 
  has 
  the 
  normal 
  rhythm 
  of 
  the 
  reproductive 
  cycle 
  been 
  

   disturbed 
  * 
  * 
  * 
  nothing 
  is 
  certainly 
  known 
  * 
  * 
  *." 
  (Her- 
  

   rick, 
  30). 
  

  

  The 
  first 
  writer 
  to 
  see 
  that 
  one 
  explanation 
  would 
  not 
  serve 
  for 
  

   all 
  the 
  different 
  groups 
  of 
  parasitic 
  birds 
  was 
  G. 
  M. 
  Allen. 
  In 
  the 
  

   chapter 
  on 
  parasitic 
  birds 
  in 
  his 
  admirable 
  book 
  (1) 
  he 
  discusses 
  all 
  

   the 
  parasitic 
  groups 
  in 
  a 
  general 
  way 
  and 
  ends 
  by 
  saying 
  that 
  one 
  

   must 
  be 
  prepared 
  to 
  find 
  that 
  the 
  parasitic 
  habit 
  has 
  been 
  acquired 
  

   in 
  more 
  than 
  one 
  way, 
  and 
  independently 
  in 
  the 
  different 
  groups 
  

   exhibiting 
  this 
  habit. 
  Wisely 
  refraining 
  from 
  offering 
  an 
  explanation 
  

   of 
  parasitism, 
  he 
  suggests 
  several 
  "possible 
  ways 
  of 
  origin." 
  One 
  

   of 
  the 
  possibilities 
  is 
  that 
  parasitism 
  may 
  have 
  arisen 
  from 
  the 
  

   occasional 
  laying 
  of 
  eggs 
  in 
  strange 
  nests 
  hj 
  birds 
  that 
  are 
  very 
  

   sensitive 
  to 
  the 
  ovarian 
  stimulus 
  provided 
  by 
  the 
  sight 
  of 
  a 
  nest 
  

   with 
  eggs 
  resembling 
  their 
  own. 
  This 
  is 
  substantiated 
  by 
  experi- 
  

   mental 
  evidence 
  collected 
  by 
  Craig, 
  who 
  found 
  that 
  in 
  doves 
  ovula- 
  

   tion 
  could 
  be 
  induced 
  by 
  comparable 
  stimuli. 
  In 
  the 
  case 
  of 
  the 
  

   flicker 
  [Colaptes 
  auraius] 
  " 
  * 
  * 
  * 
  ^^^^ 
  presence 
  of 
  a 
  nest 
  egg 
  

   seems 
  to 
  encourage 
  them 
  to 
  keep 
  on 
  laying 
  as 
  if 
  to 
  attain 
  a 
  number 
  

   whose 
  contact 
  stimulus 
  would 
  satisfy 
  the 
  brooding 
  instinct. 
  It 
  may 
  

   be 
  that 
  in 
  the 
  case 
  of 
  those 
  ducks 
  whose 
  eggs 
  seem 
  so 
  often 
  to 
  be 
  

   laid 
  promiscuouslj^ 
  in 
  nests 
  of 
  their 
  neighbors, 
  the 
  mere 
  sight 
  of 
  a 
  

   nest 
  with 
  eggs 
  resembling 
  their 
  own 
  may 
  act 
  as 
  a 
  stimulus 
  inducing 
  

   them 
  to 
  add 
  to 
  the 
  number" 
  (1). 
  Chance's 
  field 
  observations 
  on 
  the 
  

   European 
  cuckoo 
  are 
  more 
  or 
  less 
  in 
  accord 
  with 
  this 
  idea 
  as 
  he 
  believes 
  

   that 
  the 
  sight 
  of 
  her 
  victims 
  building 
  their 
  nests 
  acts 
  as 
  a 
  stimulus 
  to 
  

   ovulation 
  so 
  that 
  the 
  female 
  parasite 
  has 
  an 
  egg 
  ready 
  to 
  be 
  laid 
  five 
  

   or 
  six 
  days 
  later. 
  This 
  is 
  also 
  true 
  of 
  some 
  of 
  the 
  cowbirds. 
  

  

  However, 
  I 
  can 
  not 
  agree 
  with 
  this 
  suggestion 
  as 
  a 
  possible 
  origin 
  

   of 
  the 
  parasitic 
  habit 
  unless 
  it 
  be 
  accompanied 
  or 
  preceded 
  by 
  a 
  

   marked 
  reduction 
  in 
  the 
  attachment 
  of 
  the 
  bird 
  to 
  its 
  own 
  nest. 
  

   Even 
  if 
  the 
  sight 
  of 
  eggs 
  in 
  strange 
  nests 
  stimulated 
  egg 
  production 
  

   in 
  a 
  bird 
  that 
  was 
  not 
  parasitic, 
  its 
  natural 
  instincts 
  would 
  associate 
  

   the 
  resulting 
  eggs 
  with 
  its 
  own 
  nest 
  and 
  the 
  bird 
  would 
  probably 
  

   lay 
  them 
  there, 
  unless, 
  as 
  I 
  said 
  above, 
  its 
  attachment 
  to 
  its 
  nest 
  

   were 
  greatly 
  diminished. 
  Then, 
  too, 
  after 
  it 
  has 
  laid 
  the 
  proper 
  

   nvmiber 
  of 
  eggs, 
  "whose 
  contact 
  stimulus 
  would 
  satisfy" 
  its 
  brooding 
  

   instinct, 
  it 
  would 
  normallj'^ 
  begin 
  to 
  incubate 
  and 
  stop 
  laying. 
  If 
  

   its 
  nest 
  attachment 
  were 
  subnormal 
  in 
  strength, 
  the 
  bird 
  might 
  then 
  

   wander 
  about 
  to 
  some 
  extent 
  and, 
  on 
  receiving 
  more 
  visual 
  stimuli 
  

   might 
  revert 
  to 
  egg-laying. 
  However 
  in 
  such 
  a 
  case, 
  its 
  own 
  eggs 
  

   would 
  have 
  a 
  lessened 
  chance 
  of 
  survival. 
  

  

  