Species-Specific Responses of Bird Song Output in the Presence of Drones

Drones are now widely used to study wildlife, but their application in the study of bioacoustics is limited. Drones can be used to collect data on bird vocalizations, but an ongoing concern is that noise from drones could change bird vocalization behavior. To test for behavioral impact, we conducted an experiment using 30 sound localization arrays to track the song output of 7 songbird species before, during, and after a 3 min flight of a small quadcopter drone hovering 48 m above ground level. We analyzed 8303 song bouts, of which 2285, from 184 individual birds were within 50 m of the array centers. We used linear mixed effect models to assess whether patterns in bird song output could be attributed to the drone’s presence. We found no evidence of any effect of the drone on five species: American Robin Turdus migratorius, Common Yellowthroat Geothlypis trichas, Field Sparrow Spizella pusilla, Song Sparrow Melospiza melodia, and Indigo Bunting Passerina cyanea. However, we found a substantial decrease in Yellow Warbler Setophaga petechia song detections during the 3 min drone hover; there was an 81% drop in detections in the third minute (Wald test, p < 0.001) compared with before the drone’s introduction. By contrast, the number of singing Northern Cardinal Cardinalis cardinalis increased when the drone was overhead and remained almost five-fold higher for 4 min after the drone departed (p < 0.001). Further, we found an increase in cardinal contact/alarm calls when the drone was overhead, with the elevated calling rate lasting for 2 min after the drone departed (p < 0.001). Our study suggests that the responses of songbirds to drones may be species-specific, an important consideration when proposing the use of drones in avian studies. We note that recent advances in drone technology have resulted in much quieter drones, which makes us hopeful that the impact that we detected could be greatly reduced.

American Robin (Turdus Migratorius) Blood Lead Levels May Reflect Elevated Soil Lead Levels: Further Consequences of the Flint Water Crisis

High levels of pollutants often occur in urban environments and can pose a threat to human residents as well as local wildlife. The Flint, Michigan water crisis was caused by the corrosion of pipe infrastructure, resulting in high levels of lead (Pb) leaching into the drinking water. Irrigation with contaminated water may have introduced lead into the soil causing another source of exposure to humans as well as wildlife. A widespread songbird species, the American robin (Turdus migratorius), feeds heavily on earthworms and ingests large amounts of soil during foraging. This study investigated the impact of the Flint water crisis on American robin blood lead levels (BLL) during the breeding season in southeast MI by comparing BLL of birds captured at irrigated sites of Flint to those captured at unirrigated sites in Flint, irrigated sites in a nearby city (Ypsilanti) and rural sites. Robins captured at irrigated Flint sites had nearly double BLL compared to unirrigated Flint sites and all other control sites. Body condition declined with increasing BLL at these irrigated sites of Flint, suggesting a measurable fitness impact of lead at these levels. Because BLL in American robins is known to reflect soil lead levels and soil lead is a known driver of BLL in children, robins may act as a bioindicator for urban communities. Further research should determine the efficacy of using robin BLL as a bioindicator of soil lead and how lead might be impacting body condition and other long-term fitness metrics in urban wildlife.

Defining dual-axis landscape gradients of human influence for studying ecological processes

Ecological processes are strongly shaped by human landscape modification, and understanding the reciprocal relationship between ecosystems and modified landscapes is critical for informed conservation. Single axis measures of spatial heterogeneity proliferate in the contemporary gradient ecology literature, though they are unlikely to capture the complexity of ecological responses. Here, we develop a standardized approach for defining multi-dimensional gradients of human influence in heterogeneous landscapes and demonstrate this approach to analyze landscape characteristics of ten ecologically distinct US cities. Using occupancy data of a common human-adaptive songbird collected in each of the cities, we then use our dual-axis gradients to evaluate the utility of our approach. Spatial analysis of landscapes surrounding ten US cities revealed two important axes of variation that are intuitively consistent with the characteristics of multi-use landscapes, but are often confounded in single axis gradients. These were, a hard-to-soft gradient, representing transition from developed areas to non-structural soft areas; and brown-to-green, differentiating between two dominant types of soft landscapes: agriculture (brown) and natural areas (green). Analysis of American robin occurrence data demonstrated that occupancy responds to both hard-to-soft (decreasing with development intensity) and brown-to-green gradient (increasing with more natural area). Overall, our results reveal striking consistency in the dominant sources of variation across ten geographically distinct cities and suggests that our approach advances how we relate variation in ecological responses to human influence. Our case study demonstrates this: robins show a remarkably consistent response to a gradient differentiating agricultural and natural areas, but city-specific responses to the more traditional gradient of development intensity, which would be overlooked with a single gradient approach. Managing ecological communities in human dominated landscapes is extremely challenging due to a lack of standardized approaches and a general understanding of how socio-ecological systems function, and our approach offers promising solutions.

Nesting strategy shapes territorial aggression but not testosterone: a comparative approach in female and male birds

Our understanding of the proximate and ultimate mechanisms shaping competitive phenotypes primarily stems from research on male-male competition for mates, even though female-female competition is also widespread. Obligate secondary cavity-nesting has evolved repeatedly across avian lineages, providing a useful comparative context to explore how competition over limited nest cavities shapes aggression and its underlying mechanisms across species. Although evidence from one or another cavity-nesting species suggests that territorial aggression is adaptive in both females and males, this has not yet been tested in a comparative framework. We tested the hypothesis that cavity-nesting generates more robust territorial aggression, in comparison to close relatives with less restrictive nesting strategies. Our focal species were two obligate secondary cavity-nesting species and two related species with more flexible nesting strategies in the same avian family: tree swallow (Tachycineta bicolor) vs. barn swallow (Hirundo rustica); Eastern bluebird (Sialia sialis) vs. American robin (Turdus migratorius). We assayed conspecific territorial aggression, and found that cavity-nesting species physically attacked a simulated intruder more often than their close relatives. This pattern held for both females and males. Because territorial aggression is often associated with elevated testosterone, we also hypothesized that cavity-nesting species would exhibit higher testosterone levels in circulation. However, cavity-nesting species did not have higher testosterone in circulation for either sex, despite some correlative evidence that testosterone is associated with higher rates of physical attack in female tree swallows. Our focus on a competitive context that is relevant to both sexes – competition over essential breeding resources – provides a useful comparative framework for co-consideration of proximate and ultimate drivers of reproductive competition in females and males.

Detection of Babesia odocoilei in Ixodes scapularis Ticks Collected from Songbirds in Ontario and Quebec, Canada

Songbirds widely disperse ticks that carry a diversity of pathogens, some of which are pathogenic to humans. Among ticks commonly removed from songbirds, the blacklegged tick, Ixodes scapularis, can harbor any combination of nine zoonotic pathogens, including Babesia species. From May through September 2019, a total 157 ticks were collected from 93 songbirds of 29 species in the Canadian provinces of Ontario and Québec. PCR testing for the 18S gene of Babesia species detected Babesia odocoilei in 12.63% of I. scapularis nymphs parasitizing songbirds in Ontario and Québec; none of the relatively small numbers of Ixodes muris, Ixodes brunneus, or Haemaphysalis leporispalustris were PCR-positive. For ticks at each site, the prevalence of B. odocoilei was 16.67% in Ontario and 8.89% and 5.26% in Québec. Of 31 live, engorged I. scapularis larvae and nymphs held to molt, 25 ticks completed the molt; five of these molted ticks were positive for B. odocoilei. PCR-positive ticks were collected from six bird species—namely, Common Yellowthroat, Swainson’s Thrush, Veery, House Wren, Baltimore Oriole, and American Robin. Phylogenetic analysis documented the close relationship of B. odocoilei to Babesia canis canis and Babesia divergens, the latter a known pathogen to humans. For the first time in Canada, we confirm the transstadial passage of B. odocoilei in I. scapularis molting from larvae to nymphs. A novel host record reveals I. scapularis on a Palm Warbler. Our findings show that B. odocoilei is present in all mobile life stages of I. scapularis, and it is widely dispersed by songbirds in Ontario and Québec.

Species-Specific Responses of Bird Song Output in the Presence of Drones

Drones are now widely used to study wildlife, but applications for studying bioacoustics have been limited. Drones can be used to collect data on bird vocalizations, but an ongoing concern is that noise from the drones could change bird vocalization behavior. To test this behavioral impact we conducted an experiment using 30 sound localization arrays to track the song output of seven songbird species before, during, and after a 3-minute flight of a small quadcopter drone hovering at 50 m above ground level. We analyzed 8,303 song bouts, of which 2,285 song bouts of 184 individual birds were within 50 meters of the array centers. We used linear mixed effect models to assess patterns in song output showed patterns that could be attributed to the drone’s presence. We found no evidence of any effect of the drone for five species: American Robin Turdus migratorius, Common Yellowthroat Geothlypis trichas, Field Sparrow Spizella pusilla, Song Sparrow Melospiza melodia, and Indigo Bunting Passerina cyanea. However, we found a substantial decrease in Yellow Warbler Setophaga petechia song detections during the 3-minute drone hover, such that there was an 81% drop in detections in the 3rd minute (Wald-test, p<0.001), compared with before the drone’s introduction. In contrast, the number of singing Northern Cardinal Cardinalis cardinalis increased after the drone was introduced, and remained almost five-fold higher for 4-minutes after the drone departed (P<0.001). Further, we found an increase in cardinal contact/alarm calls when the drone was overhead, with the elevated calling-rate sustaining for 2 minutes after the drone had departed (P<0.001). Our study suggests that responses of songbirds to drones may be species-specific, an important consideration when proposing the use of drones in avian studies. We note that recent advances in drone technology have resulted in much quieter drones, which makes us hopeful that the impacts that we detected could be greatly reduced.