CSPC Bee Study
In Partnership with The American Museum of Natural History
BACKGROUND
More than 200 species of wild bees live in New York City. They have evolved alongside our native plants over thousands of years, and today, play a vital role in making our public green spaces more vibrant and securing the urban food web for creatures that depend on it.
When bees visit flowers, they collect pollen to feed their offspring and drink nectar for their own nourishment. This foraging activity pollinates the flowers, enabling them to produce seeds, nuts and fruits. About 75% of plants that humans eat depend on pollination by insects, mostly bees. Birds and other animals also depend on pollination to produce the seeds and fruits that they consume.
Public perception of bees is often confined to domesticated honeybees (Apis mellifera), which are used as a type of managed livestock for pollination services and honey production. However, honeybees, who live in large colonies, are not native to North America and their lifestyle and behaviors are different from those of our native bee species.
Understanding the geographical ranges, habitats and flight seasons of our native bees gives us baseline knowledge that we can use to monitor the health of bee populations and work to conserve an environment that provides the resources they need. Scientists today see that wild bees are vulnerable to resource and habitat loss, and they need our help much as we need theirs.
CSPC Horticulture Manager, Breeana George, examining a bumble bee at the museum lab.
Bringing awareness of native bee species to landscape managers, neighborhood stakeholders, school children and the public is an important part of pollinator conservation. Sharing knowledge leads to the development of new programs that involve citizens in conservation and helps to expand conservation efforts overall.
SITE DESCRIPTION
Carl Schurz Park (CSP) is a 15.2-acre city park along the East River on Manhattan’s Upper East Side. Gracie Mansion, home of NYC’s mayor, accounts for 1.75 acres within the park. The grounds of the mansion are inaccessible and were not part of this study. The neighborhood around CSP is heavily urbanized, containing small residential green spaces, a nearby sports field and numerous street tree pits.
CSP is located 1 mile from Central Park, 0.2 miles across the river from Lighthouse Park at the north end of Roosevelt Island, and 0.7 miles across the river from the southern end of Randalls Island. This information is important because distances to other green spaces affect the variety of species that are likely to be found within CSP. Throughout the animal kingdom, large-sized species within a genus have larger ranges than small ones. This is true of bees as well. For instance, the largest bee species may be able to move between CSP and Central Park, while the smaller ones are more likely to stay close to or within the park. At approximately 525 yards long by 145 yards wide, CSP is large enough to contain the nesting and foraging ranges for most of the smaller bees recorded (Lasioglossum, Hylaeus and Ceratina species).
Throughout the park, well-planned gardens contain a wide variety of plants, many of which are native to our region. They provide floral resources (pollen and nectar) from early spring to late fall. A focus on sustainable gardening practices conserves critical nesting habitat. Soils are heterogeneous, fallen leaves and standing dead vegetation are left in place to support bee habitat, and no harmful chemical herbicides/fungicides/pesticides are used.
SURVEY METHODS
From May through October 2019 and April through June 2021, Sarah Kornbluth or Grace Milburn collected bees by net, approximately once per week on sunny days. During the same time-period, bee bowls were deployed for additional sampling by CSP Conservancy gardeners Banford Weissmann and Breeana George twice per week on sunny days.
Netted and trapped insects were pinned and labeled by SK and GM with additional help from BW and BG. Bees were then identified by SK to species or subgenus level.
Sarah Kornbluth netting bees in the Hoop Garden.
In addition, records were pulled from GBIF which were composed almost entirely of iNaturalist observations in CSP. This dataset shows 17 species of bees that have been recorded in the park, four of which were new additions to the study.
RESULTS
Our data shows that 439 bees were collected or observed during the study period. Of these, 43 bee species were identified. Including the 4 new species from the GBIF data pull, the total number of known bee species in CSP is 47.
Bee bowls used for collecting samples.
The 200+ species of wild bee in New York City belong to six different families. We captured members of five of those families at CSP. The sixth – Melittidae – is very rare in our region and has not been collected in NYC for many years.
Table 1: Comparison of Collection Methods
In the totals at the bottom of the species list, you can see that targeted netting produced the most species and the most unique species, but observations, pan traps, and GBIF data all are important additional methods which together paint the fullest picture of the CSP bee community.
Resource Needs
Nesting habitat: The represented families (table 1) include bees that nest in a variety of substrates including; soil, pithy stems, cavities and even excavated nests in wood. Ceratina (as well as other cavity nesters) are likely already benefiting from horticultural practices that leave higher standing dead vegetation and delay composting of the previous year’s cut stems.
Floral resources: Most of the bees found in CSP are floral generalists which visit the flowers of a wide variety of plant species. However, some bees are floral specialists. The young bees (larva) of these specialists only eat pollen from the flowers of specific plants, though the adults may visit other flowers for nectar. Some mining bees (genus Andrena) are floral specialists of early spring natives, some longhorn bees (genus Melissodes) are specialists of Asteraceae, and the Blueberry Digger Bee (Habropoda laboriosa) is a specialist of Vaccinium.
Presence of Cuckoo Bees
Named after cuckoo birds, cleptoparasitic bees evolved in multiple bee families and lay their eggs in nests that are already provisioned by a host species. Populations of cuckoo bees are only present when there is a robust population of their host and the host is always more numerous than the parasite. In CSP there is a bumble bee which is a social parasite of other bumble bees, a parasite of a native leafcutter, and a parasite of a non-native leafcutter (intentional introduction of host for alfalfa pollination).
Seasonal Differences in species activity
Most of the species collected in CSP can be found within a few weeks to a month of the weather warming in early spring and will be present until the weather cools in fall. Emergence varies by species. Some species, like the social bumble bees, increase in numbers over the course of the warm season. Certain species may have multiple generations, and others do not emerge until summer.
Assortment of bees with ID tags.
The temporal survey data correlates with the approximate flight season for each species (table 2) and allows us to know which of the bees in the park we might see at different times of year. Many of the species collected are potentially present in the spring community, with Andrena, Hopitis and Osmia being active only in spring. Anthidium, some Megachile and Coelioxys usually do not emerge until late spring, and Melissodes emerge even later and are considered part of the summer bee community.
During both winter and the parts of the warm season during which they are dormant, native bee species are hibernating in their nests. Some robust bees like Bombus and Xylocopa can occasionally be seen on unseasonably warm days in late fall or even very late winter. Apis Mellifera, the European Honey Bee, does not hibernate and can also attempt to take advantage of unseasonably warm days to forage for pollen and nectar.
Table 2: Monthly collection/observation of bees from late April to early October with approximate regional flight season.
Garden Location
The location or locality of capture or observation was noted for each specimen. While walkthroughs of the park were conducted regularly to scout for blooms, collection efforts were focused on areas of pollinator activity (eg. sunny, high flower concentration, not too windy), and collection success could be affected by weather, time of day, and season. CSP is small enough that the gardens don’t indicate separate bee communities, although there may be temporary correlations with the plant communities present. Additionally, if any species are not collected from individual gardens, it does not indicate absence.
Sociality
The identified species range from solitary to eusocial in behavior. Bumble bees, European Honey Bees (aka Western Honey Bees) and some Halictidae (sweat bees and relatives) demonstrate reproductive breakdown of labor in which a queen lays the eggs and her daughter-workers don’t. Solitary species don’t have daughter-workers. Males and females mate at a certain time of year (different for different species) and then females work to build nests and collect food for their young. Once the females of solitary species have collected enough provisions, they lay an egg, close the cell, and begin the next one, never meeting their offspring. Social and solitary are not the only modes of behavior. For example, there are species where females nest in conglomerations but each have their own nest, and there are species where female sisters share a nest entrance but each provisions their own cells for their own young. In CSP there are subsocial large and small carpenter bees, the females of which may actively feed their young as they grow and keep the cells in the nest open at times.
Non-Native Species
New York has been a major port since colonization by Europeans in the seventeenth century. When humans travel, they inevitably bring flora and fauna along for the ride, either deliberately or unintentionally. Of the ten non-native bee species we collected, two were introduced deliberately. Honey bees were brought by settlers in 1620 to provide wax, and Megachile rotundata to pollinate alfalfa. Other non-native species likely came in during the shipment of goods, where they were nesting in wooden pallets or other materials.
Worth mentioning is the first NY state record of Megachile exilis parexilis, whose existence at CSP is important in our understanding of the changing ranges of native bees in the wake of climate change. Habropoda laboriosa is also great to see. This specialist of Vaccinium requires the pollen only from that plant to feed its young. While it has a large geographic range, it is uncommon throughout its range. Additionally, it is good to see a record of B. citrinus.
SHARING DATA
The results of this survey add to the baseline data on the bee community of New York City. The information we collected enables scientists to add to the knowledge of where and when species are present. Without this data, it is impossible to track changes in community composition and monitor the health of NYCs bee populations. While CSP is not a huge greenspace, it is packed full of floral resources for pollinators and has a robust bee community. Further, it has been found that cities may harbor rare species and can be important places to survey when monitoring for species that are rare or of concern. The data collected at CSP will be shared with NYC Parks and eventually added to an online database available to interested scientists.