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  1. Human activity around the globe is a growing source of selection pressure on animal behavior and communication systems. Some animals can modify their vocalizations to avoid masking from anthropogenic noise. However, such modifications can also affect the salience of these vocalizations in functional contexts such as competition and mate choice. Such is the case in the well-studied Nuttall's white-crowned sparrow ( Zonotrichia leucophrys nuttalli ), which lives year-round in both urban San Francisco and nearby rural Point Reyes. A performance feature of this species' song is salient in territorial defense, such that higher performance songs elicit stronger responses in simulated territorial intrusions; but songs with lower performance values transmit better in anthropogenic noise. A key question then is whether vocal performance signals male quality and ability to obtain high quality territories in urban populations. We predicted white-crowned sparrows with higher vocal performance will be in better condition and will tend to hold territories with lower noise levels and more species-preferred landscape features. Because white-crowned sparrows are adapted to coastal scrub habitats, we expect high quality territories to contain lower and less dense canopies, less drought, more greenness, and more flat open ground for foraging. To test our predictions, we recorded songs and measured vocal performance and body condition (scaled mass index and fat score) for a set of urban and rural birds ( N = 93), as well as ambient noise levels on their territories. Remote sensing metrics measured landscape features of territories, such as drought stress (NDWI), greenness (NDVI), mean canopy height, maximum height, leaf area density (understory and canopy), slope, and percent bare ground for a 50 m radius on each male territory. We did not find a correlation between body condition and performance but did find a relationship between noise levels and performance. Further, high performers held territories with lower canopies and less dense vegetation, which are species-preferred landscape features. These findings link together fundamental aspects of sexual selection in that habitat quality and the quality of sexually selected signals appear to be associated: males that have the highest performing songs are defending territories of the highest quality. 
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  2. Abstract

    How species interact with human‐disturbed environments is a central focus of conservation biology. Within disturbed landscapes, regenerating forests have potential to provide habitat for forest species, especially as increasing amounts of primary forest are lost. As secondary forest regenerates beside primary forest, it increases habitat heterogeneity. However, relatively little is known about the influence of habitat heterogeneity on space use. In this study, we analyzed the topography and vertical vegetation structure of regenerating forest, small forest fragments, and undisturbed rainforest in the central Amazon to determine (1) how these structural characteristics influence understory mixed‐species flock space use and (2) how the vegetative preferences of flocks varied across a disturbance gradient. We first used behavioral observations to quantify the vertical foraging niche of flocks and then associated variation in horizontal space use with the three‐dimensional features of forest structure. Surprisingly, we found that flock space use was not consistently associated with any variable, even though available habitat differed both within and across forest types. Overall, the best predictors were elevation and leaf area density within the subcanopy (16–25 m), yet most flock foraging occurred in the midstory (6–15 m). Together, these results indicate that while flocks may have certain habitat preferences, these preferences are flexible or idiosyncratic and do not correspond to a specific vertical profile. For example, flocks spent a disproportionate amount of time in low elevations when available, but not all flocks had access to low‐lying areas within their home ranges. Although other studies show flock size and diversity can be highly sensitive to habitat disturbance, mixed‐species flocks demonstrate remarkable plasticity as a unit, virtually saturating undisturbed and disturbed forest at our site, as long as regeneration has passed a certain threshold.

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  3. Abstract

    As the quality and quantity of natural habitats decrease, pressure increases to better understand species–habitat interactions and how animal communities respond to habitat changes. We assessed the relative importance of local habitat heterogeneity and productivity measures as predictors of avian species richness and compared these results to models for species of conservation concern (SCC). We derived three‐dimensional habitat heterogeneity and productivity measures from light detection and ranging data and hyperspectral imagery, and then used a Bayesian multi‐species hierarchical framework to model avian species richness and occupancy. We found both habitat heterogeneity and productivity were important factors for determining avian community richness. Three‐dimensional habitat heterogeneity and productivity metrics accurately predicted species richness at a local scale and were especially important to use within habitat guilds (i.e., alpha diversity). When scaling up to community richness across multiple habitat types (i.e., gamma diversity), two‐dimensional (surface level) productivity and heterogeneity metrics became important additions to the three‐dimensional metrics when estimating total avian richness. We also tested the utility of these metrics for predicting occupancy of SCC and compared community‐level relationships to species‐specific relationships. Species of conservation concern differed from the broader avian community with regard to local habitat heterogeneity and productivity measures. Species of conservation concern had different relationship habitat metrics than the greater avian community. Three‐dimensional measures of habitat heterogeneity and productivity predicted avian richness across the landscape, yet also highlighted the different habitat structure needs of SCC compared with the greater avian community.

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