Urbanization has contributed to the fragmentation and alteration of natural habitats around the globe, and is rapidly increasing. In this context, forested parks play a critical role for many species by providing patches of usable habitat within the urban matrix. Such patches may be particularly valuable to forest-specialists like woodpeckers (Picidae). Yet many woodpeckers require large forest patches, which are limited in fragmented landscapes. Despite their recognized value as ecosystem engineers and keystone species, almost no research exists on woodpecker ecology or space-use in urban settings. What habitat components influence woodpecker abundance and what are their functional minimum area requirements in anthropogenic landscapes? As urban development continues to expand, it is imperative that these gaps in knowledge be filled.
I examined the habitat and area requirements of five woodpecker species in 36 forest patches throughout Portland, Oregon. Woodpeckers were surveyed over two consecutive breeding seasons (2015-2016) using point counts and audio broadcast surveys. Vegetation surveys and geospatial analysis were conducted to describe the habitat and landscape composition within and around each patch. The relationship between habitat variables and woodpecker abundance was analyzed for each species using generalized linear models. Minimum area requirements were estimated based on incidence functions plotting the probability of woodpecker occurrence in forest patches of varying size.
Abundance of all five woodpecker species increased as a function of forest area and understory vegetation. The amount of tree cover in the landscape surrounding parks was important for the two largest species (Pileated Woodpeckers [Dryocopus pileatus] and Northern Flickers [Colaptes auratus]), although this variable influenced their abundance positively and negatively, respectively. Surprisingly, the degree of urbanization in the surrounding landscape was unrelated to woodpecker abundance for any species except Red-breasted Sapsuckers (Sphyrapicus ruber). Four of the five species I studied reached higher levels of abundance in natural areas (i.e. greenspaces with multistory vegetation) than traditional parks (i.e. parks managed for recreation, with cleared understories). I recommend that large, multistory forested parks be created and protected to benefit woodpeckers.
Minimum area requirements were generated for each species based on the forest patch size at which their predicted probability of occurrence reached 0.5. This corresponded to an area requirement of 51 ha for Pileated Woodpeckers and 34 ha for Hairy Woodpeckers (Picoides villosus). None of the other three woodpeckers exhibited strong area-sensitivity. These findings provide much needed information on woodpecker ecology in urban landscapes, and may offer direction for park management as rates of urbanization continue to increase.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5526 |
| Date | 07 June 2018 |
| Creators | Baz, Adam |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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