Relationships among territory size, habitat, song and nesting success of northern cardinals

-We collected data from 30 territories of Northern Cardinals (Cardinalis cardinalis) during 3 breeding seasons (1979-1981) in eastern Texas. Territory size was positively correlated with tree height and negatively correlated with the density of foliage at ground level and at 3 m above the ground, and with the density of shrubs. Nesting success was positively correlated with presence of patchy understory foliage and arthropod biomass in territories. Cardinals with low song complexity and shorter songs held better-quality territories and had better nesting success than cardinals with more complex songs. We suspect that young males may use long, complex songs to establish a territory initially, and in subsequent years put less time and effort into song and more into care and defense of young. Received 15 January 1985, accepted 7 June 1985. THE functional significance of song in birds is a widely studied phenomenon. In particular, the significance of song repertoires has recently received extensive examination, resulting in many hypotheses. Krebs (1977a) summarized these hypotheses as follows: (1) repertoires enhance individual recognition (Emlen 1971, Brooks and Falls 1975); (2) repertoires are a product of sexual selection (Catchpole 1973, Kroodsma 1977); and (3) repertoires increase success in territorial competition by allowing acquisition of larger (Krebs 1977b) or betterquality (Howard 1974) territories. Large repertoires could permit matched countersinging among males establishing or defending territories (Lemon 1968, Verner 1975) or reduce habituation of listeners (Hartshorne 1956). Krebs (1977a) suggested a new mechanism (the Beau Geste hypothesis) whereby large song repertoires could be used to create the illusion that a particular habitat area was already saturated with numerous territorial males. Holding territory size constant, repertoire size of Northern Mockingbirds (Mimus polyglottos) in central and western Texas was correlated with measurements of territory quality (Howard 1974). Male mockingbirds with larger 3Present address: Math and Science Division, Bee County College, Beeville, Texas 78102 USA. repertoires also had the highest success in excluding other males and attracting females. If males with larger repertoires or some other song characteristic are able to establish and maintain larger or better-quality territories, such males should have a higher nesting success than males with territories of lesser quality. High-quality territories should have a greater availability of food and nest concealment than low-quality territories. Females from an inbred strain of canaries (Serinus canaria) exposed to playbacks of males with large repertoires built nests faster and laid larger clutches than did females exposed to small repertoires (Kroodsma 1976). Female birds may select males on the basis of song quality or select the territory of a male because of the habitat's appearance through mechanisms similar to those by which males may identify habitat quality. If either method was used, pairs in higher-quality habitat (more food and better concealment available) might be expected to produce more eggs or young on the average than pairs in lower-quality territories. Although predation would have a substantial impact on nesting success (Best 1978), vegetation structure or quality may also have an influence on predation and nesting success of birds (Best and Stauffer 1980). Vegetation characteristics around nests were correlated with nesting success of Vesper Sparrows (Pooecetes gramineus) in a 1-yr study in West Virginia 23 The Auk 103: 23-31. January 1986 This content downloaded from 207.46.13.131 on Sat, 15 Oct 2016 04:35:18 UTC All use subject to http://about.jstor.org/terms 24 CONNER, ANDERSON, AND DICKSON [Auk, Vol. 103 TABLE 1. Characteristics of cardinal songs and 100 randomly selected syllables from 30 territories over a 3-yr period in eastern Texas. Variable code Description Mean SD