As cities grow and take over forests, the forest cover diminishes and reduces the capacity to sustain many organisms. Sometimes, creatures like the House Sparrow (Passer domesticus) or the European Starling (Sturnus vulgaris) actually benefit from human habitation. To make matters worse in this particular case, these birds are invasive species in many places like North America, so our proliferation is their proliferation and thus fuels the competition between these species and native species. Of course, native species such as the Black-capped Chickadee benefit from human habitation.
Many species suffer due to our expansion. Extinctions such as the Ivory-billed Woodpecker have gone away due to our destruction of forests.
Although we can quickly gather rough population estimates in some cases and see the decline of populations, the exact nature of the response due to urbanization is unknown in many cases. Knowing the details of how species respond to growing cities may help us conserve them by keeping the right kind of green spaces. Does a certain distribution of trees promote the use of them as homes for creatures like bats or insects?
I came across an interesting paper by Jorge A. Tomasevic and John M. Marzluff  on the Pileated Woodpecker (Dryocopus pileatus). This woodpecker is one of the world’s largest woodpeckers, and unlike smaller woodpeckers such as the Downy Woodpecker or Hairy Woodpecker, the Pileated Woodpecker is not so easily found in highly urbanized areas with few trees. This paper observed 13 Pileated Woodpeckers, each for about one year in the Washington area with radio tracking.
They found that Pileated Woodpeckers prefer habitat with larger tree diameters, but that they can still use lightly urbanized areas. Heavily urbanized areas with less than 20% of tree cover were rarely used. They also found that tree diameter was positively associated with land use, though the confidence interval $[0.00,0.056]$ for their model coefficient $\beta= 0.28$ for tree diameter is rather large. The interested reader should read the paper for more details.
I found it interesting how the authors giv evidence for the birding intuition that Pileated Woodpeckers don’t like heavily urbanized areas. Intuition is not a good guide, since sometimes animals do actually use certain types of land but are just difficult to find. Studies like this are important because it contributes to our fine-grained knowledge about how the organisms around us respond to changes in land characteristic. For example, if a land plan for a suburban area kept sufficient tree cover, that would help maintain areas usable by Pileated Woodpeckers.
Earlier, I mentioned the Ivory-billed Woodpecker. That woodpecker is most likely extinct due to intense forest-clearing. Let us hope the same fate will not befall the Pileated Woodpecker.
If you’d like to learn a little more about the Pileated Woodpecker and see what it looks like, I made a short video on it:
1. Tomasevic, Jorge A., and John M. Marzluff. “Use of suburban landscapes by the Pileated Woodpecker (Dryocopus pileatus).” The Condor: Ornithological Applications 120.4 (2018): 727-738.