DISCUSSION

The luxury effect – the relationship between urban biodiversity and human affluence – observed globally (Leong, Dunn and Trautwein 2018, Magle, Fidino, Sander, Rohnke, Larson, Gallo, Kay, Lehrer, Murray and Adalsteinsson 2021) manifests here in the behavioral resource selection by urban black-tailed deer. The greatest drivers of deer selection in this former savannah urban landscape are residential lot size and vegetation greenness (i.e., NDVI). Both are products of wealth. Oak Bay is a highly affluent neighborhood with 2022 house prices ranging from $1-12 million CAD (mls.ca). Large lots (mean = 3601 m2, s.d. = 1609, range 2530-14766) are highly manicured, with gardens offering abundant resource subsidies. Although the smaller “high density” lots in Oak Bay are not very small (mean = 679 m2, s.d. = 176, range 202-1052) and still heavily gardened and watered they are still not as strongly selected as the large lots.
Deer selection for areas with high-productivity vegetation highlights the importance of high-quality forage availability in urban deer resource selection. Higher vegetation greenness is represented in areas with healthy and dense vegetation, and is inversely linked to dry or drought conditions (Drisya and Roshni 2018). We observed a tight correlation with vegetation greenness (measured as NDVI) and the normalized difference moisture index (Supplementary Information, Fig. 1), with higher soil moisture associated with higher vegetation greenness. The unirrigated regions of this landscape experience extended summer drought; Garry Oak meadows provide dry, nutrient-poor vegetation (Barlow 2017, Fuchs 2001, GOERT 2021, Pellatt and Gedalof 2014, Pellatt, McCoy and Mathewes 2015). Parsing apart the effects of urban development is difficult in any system, as pre-development records are typically scant; but historically Cowan (1945) observed “from the standpoint of deer the food potential of a west coast climax forest is so low that over vast areas deer are almost non-existent”. At that time dense deer were only observed in regenerating forestry clearcuts. In the dry summer months, water was noted as particularly in demand, with a strong selection for plants in hygric areas (Cowan 1945). Thus, following European colonization the conversion of historically well-drained, drought-resistant Garry oak savannah ecosystems maintained by Indigenous peoples (Barlow, Pellatt and Kohfeld 2021, McCune, Pellatt and Vellend 2013, Pellatt and Gedalof 2014), to modern watered lawns and high-productivity vegetation is a key contributor to urban black-tailed deer abundance. This supports other research that shows the luxury effect is most commonly observed in arid and semi-arid landscapes, linked to irrigation and diverse plant communities (Leong, Dunn and Trautwein 2018).
Beyond the effects of natural vegetation, large residential lots are also a highly significant predictor of urban deer habitat-use in our study area. Large-sized residential lots are embedded in neighborhoods of similar-sized lots, generating low housing density. Deer are therefore likely responding to the decreased human disturbance associated with these neighborhoods, as well as higher densities of high-productivity vegetation associated with larger residential lots, and vegetative cover on lots. Neighborhoods with larger lot sizes and high investment into landscaping – features generated by financial affluence – are therefore more likely to experience higher deer use, and to perceive these interactions negatively (Wine et al. 2015).
Concentrated, high-quality resources mean deer can maintain smaller home ranges, which we observed here. Female urban deer home ranges were a quarter of the size of wild females in nearby Washington State (Bender, Anderson and Lewis 2004). Small home ranges in suburban environments have been noted by Happe (1982) and Bender, Anderson and Lewis (2004). Ideal free distribution theory suggests animals occupy the smallest areas that provide the resources they require (Fretwell 1969, Harestad and Bunnel 1979), and this phenomenon has been noted for other deer species (Said and Servanty 2005). In natural landscapes black-tailed deer strongly select shrubs (as opposed to graminoids or forbs) in early successional conifer stands (14-20 years) (Hanley 1984), and the abundance of hygric shrubs throughout large residential lots offers substantial subsidies that keep home-ranges small. People living in large residential lots tend to have the highest per capita income yet react most negatively to human-wildlife conflict (Wine et al. 2015. Thus, citizen reports of hyperabundant deer stem from peoples’ negativity bias (Jacobs & Vaske 2019; Buijs & Jacobs 2021) and repeated sightings of deer.
Citizen sightings suggested urban deer were strongly associated with golf courses and green spaces and our analysis corroborates this observation. Natural green spaces remain semi-arid oak savannahs but provide abundant escape cover; golf courses offer abundant well-watered grazing opportunities. Both parks and golf courses are elements of wealthy landscapes (Chamberlain, Henry, Reynolds, Caprio and Amar 2019, Schell, Dyson, Fuentes, Des Roches, Harris, Miller, Woelfle-Erskine and Lambert 2020), and the relationship between affluence and negativity bias towards urban wildlife (Wine et al. 2015) are bound to make these citizen sightings noteworthy.
Habitat selection by urban deer occurs on a predator-free backdrop. No wolves (Canis lupus ), cougars (Puma concolor ), or black bears (Ursus americanus ) – primary prey of Columbia black-tailed deer – live in these urban landscapes, as none were ever detected on cameras. Wolves in particular regulate black-tailed deer; in wild landscapes on northern Vancouver Island wolf control was associated with increased deer numbers; modelling (and mortality observations, (McNay and Voller 1995)) suggested that increased recruitment was the primary mechanism (Hatter and Janz 1994). Therefore, a predator-free urban environment is expected to markedly increase recruitment (and hence abundance) over natural landscapes. However, predator regulation of black-tailed deer populations is mediated by forage availability and proximity to carrying capacity; dense deer populations are less affected by predators (Ballard, Lutz, Keegan, Carpenter and deVos Jr 2001). Even if urban environments did allow predators, the abundant resource subsidies are likely to sustain abundant deer populations.