RELATIONSHIP BETWEEN PLUMAGE DIVERGENCE AND PAIRING FREQUENCY
Of 849 paired, male Golden-winged Warblers, 4.9% (n = 42) paired
with a female Brewster’s Warbler (Table 4). This backcross frequency is
5.4 times greater than the rate of primary hybridization
(χ2 = 24.29, p < 0.0001). For the 288
paired, male Blue-winged Warblers, 1.7% (n =5) paired with a
Brewster’s Warbler. Backcross frequency by male Blue-winged Warblers was
less than but not significantly different from their frequency of
primary hybridization (χ2 = 3.48, p = 0.062).
The frequency of backcrossing by male Golden-winged Warblers with
Brewster’s Warblers was 2.9 times greater than the rate for male
Blue-winged Warblers (χ2 = 4.81, p = 0.028).
Sample sizes for Lawrence’s Warblers were too small for statistical
analyses.
Of 834 paired, female Golden-winged Warblers, 4% (n = 33) formed
a backcross with a male Brewster’s Warbler (Table 5), which is three
times the rate of primary hybridization (χ2 = 16.90,p = 0.012). For the 309 paired, female Blue-winged Warblers,
3.6% (n =11) formed a social pair with a Brewster’s Warbler.
Backcross frequency by female Blue-winged Warblers was not significantly
different than their frequency of primary hybridization
(χ2 = 0.888, p > 0.10). The
frequency of backcrossing by female Golden-winged Warblers with
Brewster’s Warblers was not different than the rate for female
Blue-winged Warblers (χ2 = 0.0001, p> 0.10). Sample sizes for Lawrence’s Warblers were too
small for statistical analyses. From the pooled social pairing data
(Table 6), there was a significant, negative relationship between the
extent of plumage divergence between males and females and their
frequency of pairing corrected for random expectations (Fig. 3;observed number of pairs – expected number of pairs = 141.72 -
7.28*plumage divergence ; df = 7, r 2 =
0.66, p = 0.014).