﻿SOCIAL 
  PARASITISM 
  IN 
  BIRDS 
  PRIEDMANIT 
  369 
  

  

  it 
  seems 
  an 
  old 
  habit 
  phylogenetically 
  derived 
  from 
  the 
  ancestral 
  

   stock, 
  of 
  which 
  the 
  bay-winged 
  species 
  is 
  the 
  surviving 
  member. 
  

   Food 
  supply 
  can 
  not 
  explain 
  why 
  the 
  bay-wing 
  and 
  the 
  present 
  species 
  

   breed 
  so 
  late 
  in 
  the 
  season, 
  as 
  the 
  food 
  of 
  the 
  young 
  of 
  both 
  these 
  

   birds 
  is 
  the 
  same 
  as 
  that 
  of 
  the 
  young 
  shiny 
  cowbird, 
  which 
  is 
  an 
  early- 
  

   breeding 
  bird. 
  However, 
  the 
  bay- 
  wing 
  breeds 
  late 
  because 
  it 
  habit- 
  

   ually 
  breeds 
  in 
  old 
  nests 
  of 
  woodhewers 
  (Anumbius 
  and 
  Synallaxis) 
  

   and 
  ovenbirds 
  (Furnarius). 
  Late 
  in 
  the 
  season 
  there 
  are 
  plenty 
  of 
  

   these 
  nests 
  available, 
  while 
  earlier 
  they 
  are 
  fewer 
  in 
  number, 
  most 
  

   are 
  occupied 
  by 
  the 
  builders, 
  and 
  the 
  cowbirds 
  would 
  have 
  to 
  fight 
  for 
  

   them. 
  The 
  greater 
  ease 
  and 
  certainty 
  with 
  which 
  these 
  nests 
  could 
  

   be 
  obtained 
  later 
  in 
  the 
  season 
  probably 
  was 
  largely 
  responsible 
  for 
  

   the 
  postponement 
  of 
  the 
  breeding 
  season 
  in 
  the 
  bay-winged 
  cowbird. 
  

   The 
  present 
  bird, 
  the 
  screaming 
  cowbird, 
  shows 
  in 
  several 
  ways 
  that 
  

   it 
  is 
  an 
  offshoot 
  from 
  the 
  bay-wing 
  stock, 
  and 
  its 
  habit 
  of 
  breeding 
  

   very 
  late 
  is 
  doubtless 
  due 
  to 
  a 
  similar 
  tardiness 
  of 
  reproductive 
  season 
  

   in 
  the 
  stock 
  from 
  which 
  it 
  evolved. 
  

  

  DESERTION 
  OF 
  BREEDING 
  TERRITORIES 
  

  

  The 
  late 
  breeding 
  coupled 
  with 
  fairly 
  early 
  establishment 
  of 
  

   "territories" 
  which 
  remain 
  unused 
  for 
  a 
  considerable 
  length 
  of 
  time 
  

   has 
  brought 
  about 
  a 
  very 
  interesting 
  condition 
  in 
  the 
  screaming 
  

   cowbird, 
  namely, 
  not 
  infrequent 
  desertion 
  of 
  territories 
  before 
  egg 
  

   laying 
  commences, 
  with 
  the 
  subsequent 
  establishment 
  of 
  new 
  terri- 
  

   tories 
  later 
  as 
  the 
  reproductive 
  urge 
  becomes 
  more 
  imminent. 
  In 
  

   this 
  connection 
  the 
  following 
  observations, 
  taken 
  from 
  my 
  book, 
  are 
  

   of 
  interest. 
  

  

  In 
  Concepcion 
  district, 
  Tucuman, 
  Argentina, 
  I 
  watched 
  several 
  

   pairs 
  of 
  screaming 
  cowbirds 
  whose 
  territories 
  were 
  more 
  or 
  less 
  

   adjacent. 
  As 
  the 
  season 
  wore 
  on 
  I 
  found 
  that 
  one 
  pair 
  forsook 
  its 
  

   territory 
  and 
  disappeared. 
  The 
  male 
  of 
  this 
  pair 
  was 
  identifiable 
  

   by 
  an 
  extreme 
  harshness 
  in 
  his 
  notes. 
  He 
  and 
  his 
  mate 
  were 
  well 
  

   nigh 
  inseparable. 
  I 
  never 
  saw 
  either 
  bird 
  alone 
  or 
  more 
  than 
  a 
  couple 
  

   of 
  feet 
  away 
  from 
  the 
  other, 
  even 
  when 
  feeding 
  on 
  neutral 
  ground. 
  

   The 
  desertion 
  of 
  this 
  territory 
  took 
  place 
  between 
  the 
  22d 
  and 
  24th 
  

   of 
  November. 
  On 
  December 
  2 
  I 
  was 
  surprised 
  to 
  find 
  the 
  same 
  male 
  

   securely 
  established 
  in 
  a 
  new 
  territory 
  about 
  a 
  mile 
  away. 
  With 
  

   him 
  constantly 
  was 
  a 
  female, 
  just 
  as 
  before. 
  Whether 
  or 
  not 
  it 
  was 
  

   the 
  same 
  female 
  I 
  could 
  not 
  say, 
  but 
  of 
  the 
  identity 
  of 
  the 
  male 
  I 
  

   had 
  no 
  doubt. 
  The 
  old 
  territory 
  of 
  this 
  male 
  was 
  occupied 
  by 
  a 
  

   new 
  pair 
  of 
  birds 
  four 
  days 
  after 
  it 
  was 
  deserted 
  by 
  the 
  first 
  pair. 
  

   From 
  this 
  it 
  would 
  hardly 
  seem 
  possible 
  that 
  the 
  "fitness" 
  of 
  this 
  

   territory 
  had 
  in 
  some 
  way 
  been 
  lessened 
  to 
  the 
  extent 
  of 
  causing 
  

   the 
  original 
  pair 
  of 
  tenants 
  to 
  desert 
  it. 
  It 
  was 
  possible 
  that 
  the 
  

  

  