﻿SOCIAL 
  PARASITISM 
  IN 
  BIRDS 
  — 
  FRIEDMANN" 
  365 
  

  

  History 
  in 
  New 
  York 
  and 
  the 
  Museum, 
  fiir 
  Naturkunde 
  in 
  Berlin. 
  

   The 
  former 
  species 
  is 
  T. 
  aeneus, 
  the 
  red-eyed 
  cowbird, 
  the 
  latter 
  is 
  

   T. 
  armenti, 
  Arment's 
  cowbird. 
  

  

  Before 
  taking 
  up 
  the 
  reproductive 
  habits 
  of 
  the 
  different 
  species 
  it 
  

   is 
  necessary 
  to 
  form 
  a 
  mental 
  picture 
  of 
  their 
  phylogenetic 
  relation- 
  

   ships, 
  so 
  that 
  we 
  shall 
  be 
  able 
  to 
  fit 
  the 
  habits 
  into 
  the 
  genealogical 
  

   tree 
  of 
  the 
  group. 
  There 
  is 
  not 
  space 
  available 
  here 
  to 
  present 
  all 
  

   the 
  evidence, 
  of 
  which 
  there 
  are 
  several 
  independent 
  lines; 
  a 
  mere 
  

   diagrammatic 
  outline 
  will 
  have 
  to 
  suffice. 
  

  

  3. 
  Tangavius 
  — 
  Cassidix. 
  

  

  1. 
  A. 
  hadius 
  — 
  2. 
  M. 
  rufo-axillaris( 
  

  

  3. 
  M. 
  bonariensis 
  — 
  M. 
  ater. 
  

  

  This 
  scheme 
  of 
  relationship 
  is 
  supported 
  by 
  geographical 
  (distri- 
  

   butional) 
  data, 
  as 
  well 
  as 
  by 
  various 
  lines 
  of 
  biological 
  data 
  such 
  as 
  

   coloration, 
  song, 
  migration, 
  and 
  couitship 
  display. 
  

  

  BREEDING 
  HABITS 
  OF 
  THE 
  COWBIRDS 
  

  

  The 
  bay-winged 
  cowbird 
  is 
  in 
  every 
  way 
  the 
  most 
  primitive 
  

   species 
  of 
  the 
  group 
  and 
  probably 
  represents 
  the 
  original 
  condition 
  

   of 
  the 
  ancestral 
  cowbird 
  stock. 
  It 
  is 
  nonmigratory, 
  and 
  is 
  strictly 
  

   monogamous. 
  It 
  winters 
  in 
  flocks, 
  and 
  early 
  in 
  spring 
  the 
  indi- 
  

   viduals 
  leave 
  the 
  flock 
  in 
  pairs. 
  There 
  is 
  no 
  courtship 
  display 
  of 
  

   any 
  sort. 
  The 
  pairs 
  then 
  wander 
  about 
  looking 
  for 
  old 
  or 
  empty 
  

   nests, 
  but 
  frequently 
  fight 
  with 
  other 
  birds 
  for 
  possession 
  of 
  occupied 
  

   nests, 
  usually 
  with 
  the 
  result 
  that 
  the 
  bay 
  wings 
  succeed 
  in 
  ousting 
  

   the 
  builders 
  and 
  usurp 
  the 
  nests, 
  throwing 
  out 
  any 
  eggs 
  or 
  young 
  

   that 
  may 
  happen 
  to 
  be 
  present. 
  The 
  birds 
  then 
  breed 
  in 
  these 
  

   nests, 
  taking 
  care 
  of 
  their 
  eggs 
  and 
  young 
  as 
  do 
  ordinary 
  birds. 
  

   If 
  no 
  old 
  or 
  occupied 
  nests 
  are 
  available 
  the 
  birds 
  build 
  for 
  them- 
  

   selves 
  and 
  construct 
  very 
  creditable 
  nests, 
  indicating 
  that 
  they 
  still 
  

   possess 
  the 
  nest-building 
  instinct 
  but 
  bring 
  it 
  into 
  action 
  only 
  as 
  a 
  

   last 
  resource, 
  when 
  all 
  other 
  means 
  fail 
  them. 
  However, 
  even 
  when 
  

   (as 
  in 
  most 
  cases) 
  they 
  take 
  over 
  old 
  nests, 
  they 
  do 
  a 
  certain 
  amount 
  

   of 
  nest 
  building 
  — 
  repairing 
  or 
  adding 
  to 
  the 
  lining, 
  enlarging 
  the 
  

   entrance 
  in 
  the 
  case 
  of 
  domed 
  nests, 
  rearranging 
  small 
  twigs 
  on 
  the 
  

   outside, 
  etc. 
  Then, 
  after 
  the 
  nests 
  are 
  renovated 
  or 
  completed, 
  as 
  

   the 
  case 
  may 
  be, 
  the 
  females 
  lay 
  their 
  eggs, 
  usually 
  five 
  in 
  number, 
  

   and 
  begin 
  incubating, 
  and 
  rear 
  their 
  young 
  as 
  do 
  most 
  normal 
  nesting 
  

   kinds 
  of 
  birds. 
  

  

  The 
  screaming 
  cowbird 
  is 
  apparently 
  a 
  direct 
  evolutionary 
  off- 
  

   spring 
  of 
  the 
  bay-winged 
  stock. 
  In 
  the 
  adult 
  stage 
  the 
  plumages 
  

   of 
  the 
  two 
  species 
  are 
  very 
  different, 
  but 
  the 
  young 
  (juvenal) 
  birds 
  

   are 
  exactly 
  alike, 
  both 
  having 
  the 
  coloration 
  of 
  the 
  bay-winged 
  

   cowbird. 
  Like 
  the 
  bay 
  wing, 
  the 
  screaming 
  cowbird 
  is 
  nonmigra- 
  

  

  