Landowner Reports
Surveying

This past year’s surveys were a huge success. Unlike previous years, the Smithsonian hired coordinators to organize each survey – Maria Van Dyke tackled pollinators, Norm Bourg ran the plant surveys and Amy Johnson coordinated the bird surveys.

Altogether, our coordinators trained and deployed 58 citizen scientists to survey 26 sites on 22 properties in seven counties. Nine sites were new in 2012. We’d like to emphasize that these surveys were samples, meaning that species lists from each property are only those species identified within the 20 acre survey plots and do not represent the entirety of each property. This will be explained further for each individual survey below.

In all, VWL citizen scientists identified 390 species of plants, 115 species of pollinators and 83 species of birds in the 2012 grassland surveys. Our initial focus was to compare fields composed of native grass species (often called warm season fields) to fields of common, but introduced grass species (often called cool season fields).

Bird Survey Results

Bird surveys are carried out using a point count method whereby citizen scientists stand at predetermined points within each field and note every bird they see and hear within 100m for 10 minutes. With each field having three points, surveyors are covering at least 20 acres of grassland with each visit. Surveyors are asked to report flyovers as well as those species observed before, after and/or outside the boundaries of the survey in addition to surveyed birds although these observations are not included in the final data set. Although we recorded all bird species we were particularly interested in those species that are dependent on either grass or shrub habitats and we refer to these as target species.

Unlike pollinators, we did not see a major difference in total species richness between warm and cool season fields. However, we did see a significant difference in target species composition between the two field types. Warm season fields tended to have higher species richness of target shrubland species versus cool season fields, where as the target grassland species tended to prefer cool season sites over warm season.

Occurrence of Target Species in Native Warm Season Fields vs Cool Season Fields
Figure 1. Although we do not see any significant differences in total target species richness between warm and cool season fields (orange horizontal lines; p > 0.05), notice the difference in species composition between warm and cool season fields. Warm season fields tended to support higher richness of target shrubland birds whereas cool season fields supported more target grassland species.

When we break it down and explore the occurrence frequency of target species on warm versus cool season sites, we can get a better idea of where we are more likely to find individual species. For example, all 4 of the four sites where northern bobwhite quail (Colinus virginianus) were observed were warm season fields.

Occurrence Frequency of Target Species On Warm and Cool Season Fields
Figure 2. Occurence frequency is based on total occurrences for each species per site (16 warm season sites and 10 cool season sites). Number of sites where each species was observed is indicated by the number at the top of each bar. Brown-headed cowbird (brood parasite) and red-headed woodpecker (threatened species) are not target species but have been included for your interest.

If we move to the other side of the spectrum and look at the occurrence frequency of bobolinks (Dolichonyx oryzivorus), they are almost always found in cool season sites (0.90), although our sample size for sites containing bobolinks is extremely low (n=2). However, eastern meadowlarks (Sturnella magna), a target grassland species observed on 16 sites, also had a high occurrence frequency in cool season fields (0.70). This tells us that some of our target species are habitat specialists and therefore, landowners and managers have the opportunity to manage fields depending on the species they hope to attract.

Due to the differences in bird species composition between warm and cool season sites, we decided to test the relationships between vegetation and bird populations. Since forb richness was an important parameter in the other surveys, we compared spring forb richness and target species richness.

Effects of Spring Forb Richness on Target Bird Species Richness
Figure 3. The blue regression line indicates a positive correlation between target bird richness and forb richness in cool season fields. However, there is no correlation between the two in warm season fields as indicated by the orange regression line. Citizen scientists observed target species using forb species for nesting, cover and perching throughout the survey season. Photos by Amy Johnson.

As spring forb species richness increased, so did target bird species richness but only in cool season fields (r2 = 0.57), while forb richness in warm season fields had no significant influence on target species richness (r2 = 0.02). We do not know the reason for this finding but we speculate that target species are limited by roosting sites and the habitat structure found in warm season fields (i.e. strong clumped grasses) could serve the same function as free standing forbs (i.e. mullein, thistle) in cool season fields. This hypothesis will be studied in further detail in the coming season by identifying roosting sites in both types of fields.

Some exciting species observed in 2012 were Turkey Run’s breeding red-headed woodpeckers (Melanerpes erythrocephalus), at least 5 coveys of northern bobwhite quail at Indian Trace, and Oxbow Farm’s bobolinks, with a population estimated to be >100 individuals. We also had a number of sights that had breeding blue grosbeaks (Passerina caerulea), which was a rare sighting across all sites in previous years.

Although we had no observations of endangered loggerhead shrikes (Lanius ludovicianus) during the breeding season, there have been sightings over the winter at Blandy and Stonebridge Farm, in addition to other fields in the area. Important sightings such as these have influenced VWL to consider conducting fall and winter bird surveys to find out how habitat structure and diversity in these fields affect target species year-round.


Plant Survey Results

The plant survey protocol required surveyors to identify all plants found within 21 plots scattered throughout each 20 acre field. At the time of data collection, other features such as weather, percent cover, tallest plant, etc. are also recorded. Plants are surveyed once in the spring (May-June) and again in the summer (July-August) to account for warm and cool season plant development (total survey area 42 m2).

This years’ data revealed that forb and grass species richness for both seasons was slightly greater in warm season fields versus cool season fields.

2012 Summer Plant Richness
Figure 1. Spring and summer richness of forbs and grasses in warm and cool season sites.

At warm season sites there was a slight positive correlation (r2 = 0.14) between spring and summer forb richness. At cool season sites there was no significant correlation (r2 = 0.01) between spring and summer forb richness. These analyses demonstrate that it is correct to monitor the fields throughout the growing season because spring values do not closely track the full diversity of a site.

Occurrence frequency of forbs, for both seasons, was greater in warm season sites compared to cool season sites. However, the occurrence frequency of grasses, for both seasons, was greater in cool season fields as compared to warm season. In other words, cool season fields have denser stands of grass.

In a scatter plot comparing forb richness to grass frequency, warm season fields showed a strong negative correlation for both seasons (spring: r2 = - 0.55, summer: r2 = - 0.61).

2012 Summer Grass Frequency vs Summer Forb Richness
Figure 2. Scatter plots representing correlations of grass frequency and forb richness in spring and summer on warm and cool season sites.

On the other hand, cool season fields showed a weaker negative correlation for both seasons (spring: r2 = - 0.16, summer: r2 = - 0.10). These relationships indicate that as grass frequency increases forb richness decreases, and does so to a greater degree in warm season fields.

In addition to these relationships, we also discovered some breathtaking native plants in some unexpected places. For example, our citizen scientists found fluxweed (Trichostema brachiatum) at Indian Trace Game Preserve, a warm season field in Orange county managed for quail. We also had a rare ID of nodding lady’s tresses (Spiranthes cernula) in PEC’s Ovoka Meadow, a cool season pasture awaiting warm season grass conversion in 2014. On a negative note, the most abundant invasive species found this year across all sites were Japanese honeysuckle (Lonicera japonica) and Chinese lespedeza (Lespedeza cuneata).


Pollinator Survey Results

Pollinator surveys were carried out once in the spring (June) and again in the summer (August). Surveyors placed small colored plastic bowls filled with soapy water (also known as bee bowls) in the fields for 24 hours before collection. Specimens were then collected, washed and pinned for later identification by our pollinator experts - a team consisting of the pollinator coordinator Maria Van Dyke, Sam Droege of USGS and some well-trained citizen scientists.

This year’s data provided us with some interesting results that have raised several new questions. To start, we found that the warm season fields had significantly higher species richness than our cool season fields.

Combined Species Richness of Pollinators During 2012 Spring and Summer Surveys in Warm and Cool Season Fields
Figure 1. Spring richness (green bars) represents the total number of pollinator species found during the spring surveys. Summer richness (orange bars) represents any additional species found during the summer surveys. Black horizontal lines represent the average total species richness for warm and cool season sites (p < 0.05).

This led us to wonder how plant composition affects species richness and our most significant finding was that pollinator richness increases with summer forb richness in warm season fields (r2 = 0.36) but actually decreases with summer forb richness in cool season fields (r2 = - 0.40).

Effects of Summer Forb Richness on Pollinator Richness in Warm and Cool Season Fields
Figure 2. Blue regression line indicates a decrease in pollinator richness as summer forb richness increases in cool season fields. Orange regression like indicates the opposite in warm season fields - an increase in pollinator richness as summer forb richness increases.

This suggests that the forbs often associated with cool season fields may not support pollinator populations as well as warm season forbs. Our next step will be to determine which forbs have the most influence on pollinator populations, so that we can make recommendations to landowners wanting to increase native pollinator diversity in their fields.

We also found a positive correlation between pollinator richness estimates based on species and those based on identification only to the genus level (r2 = 0.27). This may allow us to speed up the processing of site data by identifying pollinators only to the genus level rather than to the species level which, in past years, has taken months to complete.

In addition to raising new questions about pollinator populations in warm versus cool season fields, we also identified some rare species among the 115 species found on our sites. For example, Oxbow Farm’s warm season field revealed the presence of a regionally rare species normally found in sandy habitats, a female Agapostemon splendens. Also relatively uncommon was a female Andrena gardineri found in a cool season field at Montrose. In addition, three of our sites had Ceratina mikmaqi, a new species discovered in 2011 – those sites were Blandy’s cool season field, Jones Preserve and Sunnyside Farm.

With so much richness across our sites, exotic species were surprisingly low with Apis mellifera (European honeybee) found on 21 out of 26 sites and three other exotic species appearing no more than twice (Andrena wilkella, Lasioglossum leucozonium and Megachile sculpturalis).


Coming in 2013

In 2013, we will continue to have coordinators for each survey to ease data collection, and survey protocols will likely remain the same with the exception of some minor improvements. Bird surveys will likely add surveys in the fall and winter so we will keep you posted on dates and modifications to the breeding season protocol.

We will also aim to survey 24-26 fields this year, keeping the number of sites the same as previous years. However, rather than continuing to survey sites already participating in the surveys, we will work to increase our unique samples by recruiting as many new sites as we can for the 2013 season and set some of our current sites aside for 1-2 seasons.

Attention Landowners!

Oxbow Farm
Oxbow Farm - photo by Amy Johnson

We are seeking landowners as far south as Albemarle County to as far north as Frederick County who have at least 20 contiguous acres of native warm season grasses and are willing to have their land surveyed for native plants and wildlife.

Learn More

Become a Citizen Scientist

Citizen Scientist
Photo by Amy Johnson

Every Spring, Virginia Working Landscapes recruits citizen scientists to assist with plant, bird and pollinator surveys across the Piedmont of northern Virginia, from Frederick to Albemarle County for spring and summer.

Learn More

Latest From Facebook

Get Involved


Join our mailing list


Follow Us

   

Get In Touch

Virginia Working Landscapes
Smithsonian Conservation Biology Institute
1500 Remount Road
Front Royal, Virginia 22630
 
This email address is being protected from spambots. You need JavaScript enabled to view it.
540.635.0038