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A single experienced observer (the author) used Raven Pro to collect four measures of within-song complexity from the vocal responses to stimuli: number of syllables per song, syllable diversity per song, syllable transitions per song, and song duration (as described in the ‘stimuli’ subsection). Some songs after being analysed were re- evaluated to maximise consistency. Not all focal males responded vocally to the song stimuli during the playback experiment. Song complexity therefore was not included in the analysis alongside the other eight response variables because song complexity can only be measured when vocalisations are produced. Instead, I used one-way ANOSIM and PERMANOVA tests to compare complexity of any vocal responses from focal males in response to the different stimuli. A mean of three response songs were analysed for every focal male that responded with songs.

The ANOSIM and PERMANOVA were performed using PAST software (version 2.17b) (Hammer et al. 2001). The ANOSIM and PERMANOVA tests were

113 comparisons. All other statistical procedures were conducted using SPSS (version 20.0, IBM, Chicago, IL, USA).

114

4.3 Results

In 19 of the 24 tui song playback sessions (79% of the total number of tui song playbacks), only males responded. Females responded, physically but non-vocally, to both complex song on four occasions, and simple song on one occasion. On these occasions, females approached the focal male non-aggressively and perched

alongside the focal male. More than one individual responded in 14 tui song

playback sessions (58%), and in nine of these 14 sessions (64%), the responses were exclusively to the complex song stimuli. In five of these 14 sessions (36%), males responded to both complex and simple stimuli. It is possible that other individuals aside from the focal bird responded to both the song stimuli and subsequent vocalisations of the focal male. Only the focal male's response measurements however were included in the statistical analysis.

The PCA for the response variables showed that PC1 explained 71.69% of the variance between the three groups, whereas PC2 explained 12.37% (Table 4.3). A Friedman's test on the raw response variable values for each individual revealed that there were significant differences in the strength of response across the three

different stimuli (N = 12; χ2

2 = 19.5; df: 2; P < 0.001), i.e. this allowed us to reject

the null hypothesis that there were no differences in the strength of response for all eight main variables to all three stimuli. There were also significant differences in PC1 scores between treatments (Table 4.4). Coupled with the scatterplot (Figure

115 4.4), this also suggests there were differences in the strength of response of the focal birds to the three different stimuli.

The PCA eigenvalues suggested seven of the variables were correlated (Table 4.3). A post-hoc Wilcoxon matched-pairs signed ranks test (with Bonferroni correction) was conducted on the variable that contributed the most to the variation between the groups on the first PC (closest distance to speaker [m]). This variable essentially represented these seven variables measuring the aggressiveness of response. The variable contributing the highest variance on PC2 was also selected for further analysis (total number songs produced during and post-stimulus), even though PC2 contributed little to the variance between the groups (Figure 4.4). The two variables that contributed the most to the variation between the different stimuli on PC1 and PC2 respectively were: 1. The closest distance to speaker, and 2. The total number of songs produced during/post-stimuli (total of six min). Responses of all variables to the complex song stimuli were stronger than simple and control song stimuli, suggesting complex song evoked more aggressive responses from the focal males within their territory (Table 4.3).

One-way ANOSIM and PERMANOVA tests showed a significantly stronger response of territorial males to complex song than simple (ANOSIM: N = 12; R = 0.385; P < 0.001, PERMANOVA: Pseudo F3, 12 = 7.325; P = 0.002) and control

song (ANOSIM: R = 0.995; P < 0.001, PERMANOVA: Pseudo F3, 12 = 83.35; P <

0.001) suggesting complex song stimuli evoked more aggressive responses from focal males than simple or control song.

116 Table 4.3: Eigenvalues, variance explained and factor loadings of the response variables following principal component analysis (PCA) for the response of focal males to complex, simple or control stimuli. *Variables with factor loading values greater than 0.7.

PC1 PC2

Eigenvalue 5.73 0.99

% of variance 71.69 12.37

Latency of first response to stimuli (sec)

0.91* 0.30

Latency of first flight or movement towards the speaker (sec)

0.91* 0.29

Distance from speaker after 30 sec (m)

0.88* -0.06

Distance from speaker after 2 min (m)

0.84* -0.32

Closest distance to speaker (m) 0.95* 0.12

Total number of flights towards/over/in response to stimuli

0.83* -0.37

Length of time within 2m of speaker (sec)

-0.63 0.71*

Total number of songs during and post-stimuli

117 Figure 4.4: PCA scatterplot with Eigenvalue scales along the axes (circles: complex song, squares: simple song, crosses: control heterospecific song).

118 Table 4.4: The descriptive statistics including the means ± standard error values and

P values from the Wilcoxon matched-pairs signed ranks test of the two variables that contributed the most variance in the PCA for all three stimuli types. Also shown are the mean PC1 Eigenvalue scores for each treatment. Note that only the P values for complex versus simple song are shown (N = 12).

Variable Control song Complex song Simple song Z P

Closest distance to speaker (m) 15.1 ± 0.9 0.3 ± 0.2 6.3 ± 1.6 -2.807 0.005 Total number of songs during and post- stimuli 1 ± 0 15 ± 3 7 ± 2 -1.649 0.099 PC1 Eigenvalue score 1.2 ± 0.1 -1 ± 0.1 -0.2 ± 0.2 -2.824 0.005