Filling the gap: Does emerald ash borer canopy damage affect songbird community composition in urban forest tracts?
Healthy community forests are important for recreation and the promotion of healthy air and lifestyles. This is true for human wellbeing, but even small woodlots can be critical for providing excellent habitat for wildlife. In Southern Ontario, many forest tracts are fragmented for human development and infrastructure, but still serve as refuges for wildlife including millions of migratory birds. Municipal forest tracts and urban woodlots act as islands by providing shelter and food for species residing in the surrounding natural habitat1. These small forests are threatened by emerald ash borer (EAB; Agrilus planipennis), an invasive boring beetle from Asia that arrived in North America in 20022. EAB can damage and eventually kill all 16 ash (Fraxinus spp.) species in North America of any size or age including healthy trees2. Adult female EAB lay their eggs just under the bark of ash trees3. The damage is first seen in the upper canopy because when the eggs hatch, the larvae feed on phloem tissue which inhibit the tree’s ability to distribute nutrients to the upper branches3. In Southern Ontario, both managed and natural woodlots may include large ash components. EAB is already responsible for killing millions of ash trees in the USA and Canada with billions of trees at risk2.
The canopy structure is an important criterion for returning migratory birds when choosing territory4 as a result, the tree cover in municipal forests is critical for supporting bird diversity. The impending EAB related mortality will be important for migrating and resident bird species as forest canopy changes can influence animal biodiversity5,6 and singing behaviour7 in complex ways8. First, the bird community may change as the forest canopy and understory characteristics change because what may be beneficial for some species will prove less attractive for others9,10. Second, birds that remain in poor-quality habitat may sing less in the dawn chorus as a relation to their reduced condition7, inhibiting their ability to find a mate. My research will consider ecological effects of EAB infestation on songbird diversity and signalling behaviour on a community scale in York Region, Ontario forest tracts.
Anyone who has spent time in the forest in the early morning hours of spring has heard the dawn chorus of birds. The dawn chorus occurs is the breeding season when male songbirds produce loud, distinctive songs to attract mates and defend their chosen territory against males of the same species11. It is a phenomenon that begins in the early morning hours, and for decades researchers have been waking up to listen to and record the dawn chorus to study the birds who live in the community. For my research, I deploy automated recorders in Southern Ontario forests tracts with ash composition, in order to capture bird songs at the height of their signalling behaviour7. After 48 hours, the memory cards were collected from the recorders and using bioacoustics software, I identified species in the community by their songs. The audio recordings of these male bird songs are visualized by spectrograms (visualizations of sound frequency over time scales; Figure 1). Too learn the members of the songbird community, I identify each species’ song once per recording. For the black-capped chickadee (Poecile atricapillus) I’ll note each song to measure any possible differences in signaling behavior at dawn between forest tracts with more EAB related mortality.
Fig. 1 Two sample annotated spectrograms of male songs from SM2 recordings taken on May 23, 2016 in major ash composition (>30%) in the North Forest Tract in York Region, Ontario. A) Represents 8 seconds of the dawn chorus beginning at 3:44 am. B) Represents 8 seconds beginning one hour after the start of A.
Another interesting technology employed in my research is the unmanned aerial vehicle (UAV) or drone, I use to document canopy mortality. EAB related canopy die-off can occur rapidly2, and my small, commercially produced, UAV is flown to capture cover images document additional canopy data, and archive any differences over time. Multiple UAV images are stitched together to form a mosaic that fully captures the forest canopy. We can use these composite images for an estimate of the percent canopy mortality by only selecting the dead trees (Figure 2). This is relatively easy to do because there is a tendency for dead trees to be a different colour than the living vegetation around them12. The pixels representing dead canopy can give a percentage of canopy mortality in each area.
Fig. 2 A) An unmanned aerial vehicle acquired image of emerald ash borer related ash mortality in Oakville, Ontario. B) The same image as in A, after px representing canopy mortality have been selected and filled white. In this image, 2172885 px of the total 12000000 px denotes approximately 18.1% canopy mortality.
As a Masters of Environmental Science candidate at Nipissing University and funded by an Industrial Postsecondary Scholarship by NSERC and BioForest Technologies in Sault Ste. Marie, my research considers any possible correlation between songbird community members and canopy mortality percentages. Additionally, for the black-capped chickadee I’ll compare the vocal performances of the dawn chorus across plots varying in ash canopy mortality. I hope to further our understanding on the influences biological invasions impose on native songbird community structure and signalling quality. This is especially important in the small fragmented forest tracts serving as limited habitat. In addition, I hope that my methods to use an acoustic measure of diversity and UAV acquired imagery will help create new survey methods for assessing community changes during inevitable biological invasion events.
By Mandy Ehnes
Masters of Environmental Science candidate,
1. Alvey AA. 2006. Promoting and preserving biodiversity in the urban forest. Urban For. Urban Gree. 5(4):195–201.
2. Poland TM, McCullough DG. 2006. Emerald ash borer: invasion of the urban forest and the threat to North America’s ash resource. J For. 104(3):118-124.
3. Eyles A, Jones W, Riedl K, Cipollini D, Schwartz S, Chan K, Herms DA, Bonello P. 2007. Comparative phloem chemistry of Manchurian (Fraxinus mandschurica) and two North American ash species (Fraxinus Americana and Fraxinus pennsylvanica). J. Chem. Ecol. 33(7):1430-1448.
4. Sanesi G, Padoa-Schioppa E, Lorusso L, Bottoni L, Lafortezza R. 2009. Avian ecological diversity as an indicator of urban forest functionality. Results from two case studies in northern and southern Italy. Arboriculture and Urban Forestry. 35(2):80-86.
5. Blumenrath S, Dabelsteen T. 2004. Degradation of great tit (Parus major) song before and after foliation: Implications for vocal communication in a deciduous forest. Behav. 141(8):935-958.
6. Showalter CR, Whitmore RC. 2002. The effect of gypsy moth defoliation on cavity-nesting bird communities. Forest Science. 48(2):273-281.
7. Ingebjorg JK, Otter KA, Van Oort H, Holschuh CI. 2005. Communication breakdown? Habitat influences on black-capped chickadees dawn choruses. Acta. Ethol. 8(2):111-120.
8. Drapeau P, Leduc A, Giroux J, Savard JL, Bergeron Y, Vickery WL. 2000. Landscape-scale disturbances and changes in bird communities of boreal mixed-wood forests. Ecol. Monogr. 70(3):423-444.
9. Candolin U, Voigt HR. 2001. Correlation between male size and territory quality: consequence of male competition or predation susceptibility? Oikos. 96(2):225-230.
10. Tingley MW, Orwig DA, Field R, Motzkin G. 2003. Avian response to removal of a forest dominant: consequences of hemlock woolly adelgid infestations. J. Biogeogr. 29(10-11):1505-1516.
11. Mennill DJ. 2011. Individual distinctiveness in avian vocalizations and the spatial monitoring of behaviour. Int. J. Avian Sci. 153(2):235-238.
12. Dunford R, Michel K, Gagnage M, Piegay H, Temelo ML. 2009. Potential and constraints of unmanned aerial vehicle technology for the characterization of Mediterranean riparian forest. International Journal of Remote Sensing. 30(19):4915-4935.