The Mysteries of Micro-Parks
by Jacob Drucker
Although major urban parks like Central Park and Prospect Park may attract and concentrate large quantities of migratory landbirds passing through New York City, birders seem to be increasingly aware that these migrant meccas are not the only places to seek local avian diversity. In recent years, people have come to embrace the potential offered by micro-parks as places to search for birds, with findings that never cease to amaze birders and casual pedestrians alike. From the sheer numbers of White-throated Sparrows that can be found in the Broadway green or a neon Blackburnian Warbler stopping at a birdbath in a Bushwick backyard, to mega-rarities like the Scott's Oriole in Union Square several years ago or the recent celebrity Couch's Kingbird frequenting Abingdon Square, the streets and small parks of urban New York hold endless surprises.
Bryant Park, surrounded by gargantuan office buildings in midtown Manhattan, has fast become an icon of just how productive micro-parks can be. eBird (http://ebird.org/ebird/hotspot/L683555) shows that a little less than half the species diversity found in Central has been found in Bryant. This diversity currently includes six species of flycatcher and thrush, 13 species of sparrow, and 28 species of warbler—pretty amazing considering Bryant Park is less than one percent the size of Central Park. Does this suggest that in any given three hectares of Central Park you could find about half its avian diversity? Or does this suggest Bryant Park concentrates birds just like Central Park does, just on a smaller scale?
Though birds concentrate into Central Park, their distributions within it are dependent on the availability of food, which leads them to the best possible habitat. This explains why bird diversity is not evenly distributed across the park. For example why, on average, can more species be found in the northern end of the park, where there are ample woodlands, thickets, weedy edges, and fresh water, versus the southern end which is mostly lawns and tourists (though both ends of Central and Bryant all have ice-skating rinks)? So whether or not you can find all of Central Park’s diversity in just three hectares depends on which three hectares you are in.
Meanwhile, in Bryant Park habitat is less spread out, but comes in more limited forms. Instead of classic woodland, there are looming, evenly spaced London Plane trees. In the place of thickets, there are hedges. Weedy fields are replaced by simple lawns, and fresh water comes in the form of puddles. Any bird attempting to survive needs to be an opportunist. Fortunately, migrating birds are some of the world's most ambitious risk takers, and spending a few days scrounging around Bryant Park is nothing compared to flying across the Gulf of Mexico. Any potential food item a bird can find is fair game, and is often enough to fuel a bird for the next leg of its journey.
Bryant Park, however popular among birders, is merely one of many micro-parks in southern Manhattan. Madison, Union, Washington, and Tompkins Square Parks are all well-travelled parks in the heart of downtown. Should they all host the same number of species and individual birds as each other? Out of the parks listed above, smaller Madison and Union have more species documented in eBird than the larger Washington and Tompkins, although there is more data for the former two (see figure 1).
What variables might determine this? The size of the park and the quality of the available habitat immediately come to mind, but other factors are likely at play as well. How much disturbance from pedestrians or dogs is there? How many other small parks are there in the vicinity that birds could filter into and thus dilute the concentration effects? How tall are the surrounding buildings and how much ambient light do they produce? Luminescence could disorient the birds into descending into the park. If the park itself is lit up, it may stand out as a beacon in its own right, particularly if green foliage is illuminated. The park’s geographic location may also play in, particularly if it is along the waterfront or the ridges in northern Manhattan, which birds use to orient. Competition from invasive species such as House Sparrows and European Starlings may also influence a migrant’s decision to stick around in a park where finding food is enough of a challenge, let alone defending an already obtained item from a bully. Even temperature can influence the productivity of a micro-park, as ambient city heat can make all the difference in survival for half-hardy species during the winter that would typically be farther south.
Interestingly enough, variables such as size, degree of isolation, and amount of available habitat have been modeled extensively by the ecologists Robert MacArthur and Ed Wilson in their theory of Island Biogeography as an attempt to predict species diversity and abundance on oceanic islands. Though these models were designed with resident, not migratory, species in mind, the same phenomena might still be applicable to birds seeking temporary refuge on islands of green in a sea of concrete. Generally speaking, species diversity should be highest on larger “islands” that are close to a “mainland” of sorts, while diversity should be lowest on small, distal “islands.” In a classical sense, this phenomenon is reflected by the fact that Martha’s Vineyard has more breeding species than Block Island.
In the context of urban micro-parks, these principles of Island Biogeography imply that Bryant Park’s high species list is due to its close proximity to Central Park—a potential source for its diversity.
Meanwhile, a small park like St. Johns Park in Tribeca is not only small, but isolated, so is less likely to receive birds that were previously using a larger patch of green.
Nonetheless, one could also argue that isolation is beneficial to a park’s species list, as it will be a more effective migrant trap. Another explanation for Bryant Park apparently attracting and retaining more birds than Union Square Park or Madison Square Park is the lack of other parks nearby—there are no other parks larger than a hectare within half a mile of Bryant. Meanwhile, Madison, Union, and Tompkins Squares, Gramercy Park, Stuyvesent Square, and Stuyvesant Town form a cluster, with no greater than a quarter-mile between each one. Could this be diluting each park’s ability to concentrate birds? Do migrants shuttle back and forth between these proximal parks to the point where the cluster could be thought of as one large park in terms of a biogeographical analysis?
MacArthur and Wilson’s original models were based on an experiment in the Caribbean, where they killed off insect populations on tiny mangrove islands, and documented the process of repopulation through colonization over the course of several years. They then extrapolated their results to explain patterns of bird communities on larger islands. However, these patterns of colonization deal in terms of resident, breeding, or wintering species, which take generations to establish a stable presence on the island. Migratory species, on the other hand, use an area only temporarily, and turnover of individuals and species is far more rapid. Though the principle of island biogeography may be applied to migrants using both oceanic islands and urban parks, it is worth considering this difference in operant temporal scales.
It is clear that there is no one simple predictor of avian diversity in micro-parks. But there is a very simple explanation for why some parks have more species recorded than others: observer bias (David Krauss, personal communication). Without similar quantities of information about the occurrence of bird species in each park, it is impossible to discern whether higher species totals are due to the factors discussed above, or simple probabilities of detection. eBird—which has become an effective representation of how thoroughly an area has been birded in NYC in the past 10 years—shows just how relatively data-deficient many micro-parks are (see table 1). Defining a micro-park as an isolated patch of vegetation in the city smaller than 15 hectares, out of Manhattan’s 25 micro-park eBird hotspots with any data at all, only four of them have more than 50 checklists entered. These do not represent all the various small squares, circles, gardens, and parks in New York County, but Manhattan does have more micro-park hotspots than any other borough (see figure 2). In Brooklyn the only micro-park hotspots away from the waterfront are Fort Greene, McGrolick, and Cooper Parks. Similarly, Staten Island has six, Queens has four, and the Bronx has three. Checklists almost certainly exist for various small parks in the form of Personal Locations, but without Hotspot status, data from different observers at a single site will not be pooled into a central, publicly accessible source of information about the occurrence of birds there.
Fortunately, this problem is relatively easy to solve. The more people who get out and bird their local patch of greenery, enter their observations into eBird, making sure to use a public eBird hotspot—or suggest a new one—the closer we will be to piecing together the puzzles presented by micro-parks. New hotspots can be suggested in two ways: when you create a new personal location, there will be a box to check and a prompt to suggest the location as a hotspot right under the new location's name. To suggest a personal location that already exists as a hotspot, go to “Manage my Locations” on the right and side of the “My eBird” page. Click “edit,” and at the top of the hotspot's page, under its name, you will see a prompt to “suggest as hotspot.” If the location is publicly accessible, suggest it! If you have a personal location you think might already be a hotspot, “edit” the location, and select the option to “merge” data from your personal location with that under the public hotspot. More information on which locations are appropriate for hotspots, how to name them, and more can be found at http://help.ebird.org/customer/portal/articles/1006824-what-is-an-ebird-hotspot-.
Additionally this year is an especially exciting one for eBirding in New York City, as it is the world’s first official Urban Birding Challenge (http://www.urbanbirdingchallenge.com). This global event pitches cities across the globe against one another in friendly competition to find the most species in a calendar year. eBird will be used as the official scorekeeper, so keep those checklists rolling in! If it’s not in eBird, it doesn't count. Aside from being a new spin on the concept of a Big Year, the UBC also represents a great chance for education and outreach, as a way to show wildlife-repressed city dwellers just how biodiverse urban areas can be.
Few places are better for pleasantly surprising non-birders with the feathered gems in their neighborhood than micro-parks. It might be easy for people to associate bird diversity with larger parks, but many people seem to be utterly amazed to find out how many different kinds of birds can appear right outside their apartment windows. Especially when many birders gather in numbers on the streets or in a small park, pedestrians are often inquisitive about the crowd. It can be wonderful to see how excited people ranging from toddlers to truck drivers to celebrities get once enlightened with the sight of something like Cerulean Warbler zipping through the oaks on an Upper West Side street, a Couch’s Kingbird hawking spiders from a fire escape in Greenwich Village, or even a Red-tailed Hawk devouring a squirrel in a community garden. For many people this previously unnoticed parallel universe of bird life triggers a completely new perspective on city living, and many even become birders or other couriers of natural history.
Fathoming the patterns occurrence of birds is not an easy task. For much of the world, it remains a major challenge. Sites of interest are often spread out, as are birders and ornithologists who are interested in such patterns. Small urban parks represent a unique system in this respect, as they are small, in relatively close proximity to each other, and in densely populated areas with lots of birders. Each time you bird your local square, plaza, or garden, and make the information accessible by entering it to eBird, we are one step closer not just to piecing together the mysteries of micro-parks, but also to understanding why looking for birds in the heart of urbanity is so much fun and exciting.
Table 1: New York City Micro-Parks
Summary of species totals, number of checklists, and area for each New York City micro-park hotspot with data in eBird. Data taken from eBird on 1/11/15, and area measured approximately using Google Earth Pro. “Micro-Park” here refers to a small park or patch of vegetation less than 15 hectares. Hotspots on the waterfront are not included, as species totals often include waterfowl, which skews the basis of comparison when considering land-locked parks.
|Park||Number of Species||Number of Checklists||Area (Hectares)|
|Tudor City Greens||68||5||0.82|
|Dag Hammrskjold Plaza||44||5||0.74|
|Tudor City Greens—South||38||8||0.48|
|Tudor City Greens—North||33||16||0.34|
|50th Street/6th/7th Avenue||26||156||0.70|
|City Hall Park||23||10||3.85|
|Jefferson Market Garden||19||5||0.37|
|Washington Market Park||15||4||0.67|
|Battery Park City – Teardrop Park||4||2||0.66|
|Fort Greene Park||36||5||12.26|
|Mt. Olivet Cemetery||38||5||143.00|
|Queens Hospital Center||7||2||2.00|
|Mill Pond park||9||2||2.00|
|Satellite Academy HS Community Garden||6||6||0.01|
|King Fisher Pond Bluebelt||99||21||9.86|
|Unnamed Park at Carleton Ave||17||2||0.60|
|Bloesser's Pond State Wetland||16||2||6.90|
|Staten Island University Hospital||14||29||5.67|
|Ramona Ave Retention Ponds||13||2||0.66|
|Huguenot Ponds Park||13||4||1.37|