﻿SOCIAL 
  PARASITISM 
  IN 
  BIRDS 
  —FBIEDMANN 
  371 
  

  

  pair 
  off 
  regularly 
  and 
  each 
  pair 
  has 
  its 
  own 
  territory. 
  In 
  places 
  

   where 
  the 
  cowbird 
  population 
  is 
  great, 
  the 
  birds 
  still 
  pair 
  off, 
  but 
  

   inasmuch 
  as 
  they 
  make 
  no 
  pretense 
  of 
  protecting 
  the 
  territory 
  other 
  

   individuals 
  filter 
  in, 
  remain 
  there 
  a 
  day 
  or 
  so 
  and 
  then 
  pass 
  on. 
  

   Consequently 
  it 
  is 
  more 
  usual 
  to 
  see 
  several 
  of 
  these 
  birds 
  together 
  

   (with 
  the 
  males 
  predominating 
  in 
  number) 
  than 
  to 
  see 
  them 
  in 
  groups 
  

   of 
  twos. 
  The 
  following 
  observations, 
  taken 
  from 
  my 
  book 
  (23), 
  will 
  

   illustrate 
  this 
  point. 
  I 
  watched 
  a 
  certain 
  pair 
  of 
  shiny 
  cowbirds, 
  

   whose 
  territory 
  I 
  knew, 
  every 
  day 
  for 
  several 
  weeks. 
  The 
  female 
  

   laid 
  the 
  first 
  egg 
  in 
  a 
  nest 
  of 
  a 
  Chingolo 
  song 
  sparrow 
  {Brachyspiza 
  

   capensis) 
  on 
  October 
  25. 
  

  

  I 
  was 
  surprised, 
  however, 
  to 
  find 
  that 
  another 
  female 
  cowbird 
  also 
  laid 
  in 
  this 
  

   aest 
  on 
  the 
  same 
  date. 
  It 
  looked 
  as 
  though 
  the 
  male 
  was 
  constant 
  in 
  its 
  territorial 
  

   relations 
  but 
  that 
  females 
  came 
  and 
  went 
  promiscuously. 
  However, 
  in 
  the 
  next 
  

   few 
  days 
  I 
  found 
  that 
  the 
  same 
  female 
  had 
  laid 
  an 
  egg 
  in 
  each 
  of 
  four 
  chingolo 
  

   nests 
  in 
  this 
  territory, 
  including 
  nest 
  No. 
  1. 
  The 
  eggs 
  were 
  laid 
  at 
  intervals 
  of 
  one 
  

   day, 
  but 
  at 
  the 
  same 
  time, 
  each 
  day 
  I 
  kept 
  finding 
  eggs 
  of 
  other 
  female 
  cowbirds 
  

   in 
  nests 
  where 
  they 
  certainly 
  were 
  not 
  the 
  day 
  before. 
  Thus 
  in 
  nest 
  1 
  no 
  less 
  than 
  

   four 
  different 
  female 
  cowbirds 
  deposited 
  one 
  egg 
  each, 
  two 
  of 
  them 
  removing 
  (or 
  

   apparently 
  removing) 
  one 
  of 
  the 
  eggs 
  already 
  in 
  the 
  nest. 
  In 
  nest 
  No. 
  2, 
  eggs 
  

   were 
  deposited 
  by 
  two 
  different 
  cowbirds; 
  nest 
  No. 
  3 
  contained 
  eggs 
  of 
  two 
  

   different 
  cowbirds; 
  nest 
  No. 
  4 
  contained 
  only 
  1 
  cowbird 
  egg. 
  All 
  in 
  all 
  I 
  judged, 
  

   by 
  the 
  size, 
  color, 
  marking, 
  and 
  texture 
  of 
  the 
  eggs 
  as 
  well 
  as 
  by 
  the 
  date 
  of 
  deposi- 
  

   tion 
  that 
  no 
  less 
  than 
  six 
  different 
  females 
  had 
  deposited 
  eggs 
  in 
  nests 
  within 
  the 
  

   limits 
  of 
  this 
  particular 
  territory. 
  However, 
  the 
  important 
  point 
  is 
  that 
  one 
  bird, 
  

   which 
  I 
  shall 
  call 
  the 
  real 
  mate 
  of 
  the 
  male 
  whose 
  territory 
  is 
  under 
  discussion, 
  

   laid 
  an 
  egg 
  in 
  each 
  of 
  the 
  four 
  nests, 
  or 
  four 
  eggs 
  in 
  all, 
  while 
  of 
  the 
  other 
  five 
  

   females 
  using 
  these 
  nests, 
  four 
  laid 
  but 
  one 
  egg 
  apiece 
  and 
  the 
  other 
  laid 
  two. 
  

   Furthermore 
  the 
  two 
  eggs 
  laid 
  by 
  the 
  last 
  bird 
  were 
  laid 
  four 
  days 
  apart. 
  This 
  

   means 
  either 
  that 
  this 
  particular 
  female 
  wandered 
  about 
  from 
  one 
  territory 
  to 
  

   another 
  or 
  else 
  that 
  it 
  laid 
  during 
  the 
  interval 
  in 
  nests 
  in 
  this 
  territory 
  which 
  I 
  

   never 
  found. 
  

  

  Nevertheless, 
  in 
  spite 
  of 
  all 
  this 
  confusing 
  data 
  the 
  total 
  evidence 
  leads 
  me 
  to 
  

   believe 
  that 
  the 
  shiny 
  cowbird 
  is 
  chiefly 
  monogamous 
  and 
  each 
  mated 
  female 
  

   sticks 
  to 
  one 
  territory 
  but 
  that 
  both 
  the 
  sexual 
  and 
  territorial 
  relations 
  are 
  so 
  

   weak 
  as 
  to 
  be 
  very 
  easily 
  modified 
  or 
  sometimes 
  even 
  destroj^ed 
  by 
  conditions, 
  

   particularly 
  by 
  the 
  unnatural, 
  increased 
  density 
  of 
  cowbird 
  population 
  per 
  given 
  

   area 
  around 
  cultivated 
  districts. 
  Of 
  course 
  this 
  frequently 
  results 
  in 
  what 
  seems 
  

   to 
  be 
  sexual 
  promiscuity 
  and 
  does 
  destroy, 
  in 
  great 
  measure, 
  the 
  "territory," 
  in 
  

   the 
  sense 
  that 
  that 
  particular 
  area 
  is 
  no 
  longer 
  the 
  domain 
  of 
  only 
  one 
  female 
  but 
  

   has 
  become 
  the 
  happy 
  hunting 
  grounds 
  of 
  all 
  that 
  may 
  care 
  to 
  make 
  use 
  of 
  it. 
  

   The 
  same 
  is 
  largely 
  true 
  for 
  the 
  North 
  American 
  species, 
  Molothrus 
  ater. 
  

  

  One 
  more 
  point 
  needs 
  to 
  be 
  discussed 
  here. 
  The 
  males 
  outnumber 
  the 
  females 
  

   to 
  the 
  same 
  extent 
  as 
  they 
  do 
  in 
  M. 
  ater 
  of 
  North 
  America 
  — 
  about 
  3 
  males 
  to 
  every 
  

   2 
  females. 
  Assuming 
  that 
  every 
  breeding 
  female 
  has 
  a 
  mate 
  and 
  but 
  one 
  mate, 
  

   there 
  would 
  be 
  still 
  one-third 
  of 
  the 
  males 
  without 
  mates 
  and 
  consequently 
  with- 
  

   out 
  anj' 
  means 
  of 
  satisfying 
  their 
  sexual 
  desires. 
  If 
  several 
  males 
  having 
  no 
  

   ''territories'' 
  or 
  "spheres 
  of 
  influence" 
  joined 
  in 
  the 
  pursuit 
  of 
  the 
  same 
  female, 
  

   disaster 
  to 
  the 
  race 
  would 
  undoubtedly 
  ensue. 
  But 
  each 
  male 
  (except 
  in 
  the 
  case 
  

   of 
  the 
  yearling 
  birds 
  that 
  begin 
  breeding 
  very 
  late) 
  has 
  his 
  own 
  territory 
  and 
  there 
  

   he 
  awaits 
  the 
  coming 
  of 
  a 
  mate. 
  The 
  greater 
  the 
  iniraber 
  of 
  cowbirds 
  to 
  a 
  given 
  

  

  82322—30 
  25 
  

  

  