﻿376 
  ANNUAL 
  REPOET 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  111 
  the 
  other 
  two 
  species, 
  where 
  the 
  parasitic 
  liabits 
  are 
  better 
  developed, 
  the 
  

   territories 
  are 
  distinct 
  chiefly 
  in 
  districts 
  where 
  the 
  species 
  are 
  not 
  abnormally 
  

   numerous; 
  but 
  where 
  they 
  are 
  unnaturally 
  abundant, 
  the 
  territorial 
  instincts 
  are 
  

   not 
  strong 
  enough 
  to 
  stand 
  unmodified 
  against 
  the 
  pressure 
  of 
  cowbird 
  population. 
  

   Distinctness 
  of 
  terrritory 
  depends 
  on 
  the 
  amount 
  of 
  what 
  may 
  be 
  called 
  "territoiia! 
  

   protection" 
  diyplaj'ed 
  by 
  the 
  male. 
  In 
  most 
  birds 
  the 
  male 
  establishes 
  a 
  breeding 
  

   territory 
  and 
  protects 
  it 
  from 
  the 
  inroads 
  of 
  other 
  males 
  of 
  its 
  own 
  species. 
  

   The 
  female 
  sometimes 
  has 
  this 
  instinct 
  as 
  well. 
  In 
  the 
  parasitic 
  cowbirds 
  we 
  

   see 
  that 
  the 
  birds 
  have 
  still 
  retained 
  the 
  territorial 
  desire 
  but 
  have 
  lost 
  most 
  of 
  

   the 
  instinct 
  to 
  protect 
  their 
  breeding 
  areas. 
  The 
  original 
  factor 
  involved 
  in 
  this 
  

   loss 
  is 
  the 
  reversal 
  of 
  the 
  usual 
  method 
  of 
  territorial 
  acquisition 
  in 
  the 
  most 
  primi- 
  

   tive 
  of 
  the 
  cowbirds. 
  We 
  have 
  seen 
  that 
  birds, 
  usualh' 
  the 
  males, 
  establish 
  their 
  

   territories, 
  and 
  then. 
  choose 
  a 
  nesting 
  site 
  somewhere 
  within 
  that 
  territory. 
  The 
  

   bay-winged 
  cowbirds, 
  however, 
  reverse 
  this 
  process. 
  They 
  leave 
  the 
  winter 
  flocks 
  

   in 
  pairs 
  and, 
  instead 
  of 
  staking 
  out 
  their 
  "claims" 
  they 
  look 
  for 
  old 
  or 
  even 
  new 
  

   nests 
  in 
  which 
  to 
  breed. 
  They 
  fight 
  for 
  these 
  nests 
  if 
  necessary, 
  and 
  when 
  once 
  

   in 
  occupation, 
  they 
  extend 
  the 
  territory 
  radially 
  around 
  the 
  nest. 
  In 
  this 
  way 
  

   the 
  territory, 
  instead 
  of 
  being 
  the 
  primary 
  consideration, 
  becomes 
  a 
  matter 
  of 
  

   onlj' 
  secondary 
  importance 
  and 
  with 
  this 
  reduction 
  of 
  its 
  significance, 
  the 
  instinct 
  

   to 
  defend 
  it 
  is 
  correspondingly 
  lessened. 
  In 
  this 
  way 
  the 
  amount 
  of 
  "territorial 
  

   protection" 
  displayed 
  by 
  the 
  male 
  II-: 
  decreased 
  and 
  in 
  the 
  more 
  recent, 
  parasitic 
  

   species, 
  where 
  the 
  protecting 
  instincts 
  are 
  further 
  reduced, 
  the 
  territory 
  of 
  any 
  

   one 
  male 
  is 
  very 
  apt 
  to 
  be 
  invaded 
  by 
  other 
  males 
  of 
  its 
  own 
  species. 
  

  

  Furthermore, 
  in 
  the 
  bay-winged 
  cowbird, 
  we 
  have 
  seen 
  that 
  the 
  female 
  has 
  lost 
  

   most 
  of 
  her 
  protecting 
  instinct 
  and 
  seems 
  to 
  spend 
  most 
  of 
  w 
  hat 
  she 
  has 
  before 
  lay- 
  

   ing 
  her 
  eggs, 
  after 
  which 
  the 
  eggs 
  are 
  largely 
  dependent 
  on 
  the 
  male 
  for 
  protection. 
  

   The 
  female 
  is 
  always 
  quite 
  bold 
  and 
  fearless 
  when 
  away 
  from 
  the 
  nest, 
  but 
  very 
  

   shy 
  and 
  nervous 
  when 
  incubating. 
  Apparently 
  she 
  has 
  the 
  instinct 
  to 
  conceal 
  her 
  

   eggs 
  in 
  a 
  nest, 
  usually 
  not 
  of 
  her 
  own 
  building, 
  but 
  has 
  very 
  little 
  desire 
  to 
  protect 
  

   them 
  once 
  they 
  are 
  laid. 
  If 
  not 
  for 
  the 
  protection 
  of 
  the 
  male 
  (and 
  very 
  fearless 
  

   he 
  is), 
  she 
  would 
  probably 
  be 
  unable 
  to 
  care 
  for 
  her 
  eggs, 
  and 
  if 
  the 
  male 
  should 
  

   lose 
  his 
  protecting 
  instinct 
  the 
  result 
  would 
  be 
  that 
  the 
  female 
  would 
  have 
  the 
  

   instinct 
  to 
  lay 
  (or 
  conceal) 
  her 
  eggs 
  in 
  nests 
  but 
  not 
  to 
  care 
  for 
  them 
  (or 
  protect 
  

   them) 
  . 
  This 
  would 
  open 
  an 
  easy 
  path 
  to 
  parasitism. 
  If 
  we 
  reexamine 
  the 
  habits 
  

   and 
  instincts 
  of 
  other 
  cowbirds 
  we 
  find 
  that 
  this 
  is 
  exactly 
  what 
  has 
  happened. 
  

   The 
  males 
  have 
  lost 
  their 
  protecting 
  instincts 
  and 
  we 
  find 
  that 
  the 
  loss 
  is 
  more 
  com- 
  

   plete 
  in 
  M. 
  ater 
  and 
  M. 
  bonariensis 
  than 
  in 
  M. 
  rufo-axillaris. 
  The 
  very 
  fact 
  that 
  

   we 
  still 
  find 
  these 
  somewhat 
  obscure, 
  but 
  yet 
  real, 
  stages 
  in 
  the 
  loss 
  of 
  the 
  protect- 
  

   ing 
  instincts, 
  only 
  serves 
  to 
  emphasize 
  the 
  downward 
  path 
  these 
  instincts 
  have 
  

   taken. 
  So 
  then, 
  it 
  may 
  be 
  said 
  that 
  the 
  immediate 
  cause 
  of 
  the 
  origin 
  of 
  the 
  para- 
  

   .sitic 
  habit 
  in 
  the 
  cowbirds 
  was 
  the 
  loss 
  of 
  the 
  protecting 
  instinct 
  of 
  the 
  male. 
  The 
  

   fact 
  that 
  the 
  female, 
  still 
  earlier 
  in 
  the 
  history 
  of 
  the 
  group, 
  lost 
  most 
  of 
  her 
  pro- 
  

   tecting 
  instincts 
  can 
  not 
  be 
  called 
  a 
  causitive 
  factor 
  because 
  as 
  long 
  as 
  the 
  male 
  

   retained 
  his 
  instincts 
  of 
  defense, 
  as 
  in 
  the 
  bay-winged 
  cowbird 
  to-day, 
  the 
  birds 
  

   were 
  not 
  parasitic. 
  What 
  caused 
  the 
  almost 
  complete 
  loss 
  of 
  these 
  instincts 
  in 
  the 
  

   male 
  we 
  can 
  not 
  definitely 
  say, 
  but 
  the 
  factor 
  which 
  started 
  the 
  weakening, 
  and 
  

   finally 
  brought 
  about 
  their 
  destruction 
  was 
  the 
  reversal 
  of 
  the 
  territorial 
  and 
  nest- 
  

   ing 
  habits. 
  When 
  the 
  territory 
  became 
  of 
  only 
  secondary 
  importance 
  the 
  impulse 
  

   to 
  protect 
  it 
  was 
  correspondingly 
  weakened. 
  At 
  the 
  risk 
  of 
  seeming 
  paradoxical 
  

   it 
  might 
  almost 
  be 
  said 
  that 
  the 
  fact 
  that 
  the 
  ancestral 
  cowbirds 
  cared 
  more 
  about 
  

   the 
  nest 
  than 
  the 
  territory 
  had 
  much 
  to 
  do 
  with 
  the 
  origin 
  of 
  the 
  parasitic 
  habit. 
  

   The 
  complex 
  of 
  reproductive 
  instincts 
  became 
  unbalanced 
  and 
  eventually 
  collapsed. 
  

   In 
  other 
  v.ords, 
  tlie 
  birds 
  were 
  more 
  interested 
  in 
  a 
  secondary 
  than 
  a 
  primary 
  

   consideration 
  with 
  the 
  result 
  that 
  the 
  former 
  suffered 
  much 
  more 
  than 
  the 
  latter 
  

  

  