Practice description
The maintenance, through mowing or haying, of cool season grasslands for the benefit of grassland birds like Bobolinks and Eastern Meadowlarks. The primary issue faced by managers of cool season grasslands is striking a balance between ensuring high quality grassland habitat (which typically requires growing season mowing to suppress woody and clonal forb cover) while allowing grassland bird populations enough time to successfully fledge their young in these settings. Often agricultural values must be considered, as most cool season grasslands in Massachusetts are active hayfields.
This practice is primarily relevant to Cultural Grasslands. Some grassland birds, most notably the state-listed Grasshopper Sparrow, prefer Sandplain Grassland habitat. For information about management of Sandplain Grasslands (warm season grasslands) click here. Not all cultural grasslands are large enough to support grassland birds, and managers may have other goals such as the maintenance of pollinator or turtle nesting habitat. For information about the general management of cultural grasslands, see mowing and mulching.
Associated practices
The plant species that comprise a high-quality hay crop (timothy, orchard grass, tall fescue, alfalfa) also provide the optimal composition and structure to support cool season grassland-obligate birds (bobolink). Therefore, the best management practices for hay production – with harvest strategies altered to accommodate breeding bird populations – should be employed whenever Grassland Bird Management is achieved by hay production. These practices may include the application of soil amendments, herbicide use to control woody, clonal and invasive species, and tree removal along hedgerows to defragment grassland areas. These complementary practices will also often be important to maintain optimal habitat in non-agricultural cool season grassland situations.
Methods
From a conservation perspective, there are two primary goals that apply to the management of cool season grasslands for grassland birds that apply whether the management is achieved through hay production or non-agricultural mowing:
- Controlling woody, clonal and invasive species in favor of cool season grasses such as timothy, orchard grass and tall fescue;
- Strategizing mowing practices, particularly timing, to ensure that cool season grasslands will contribute positively to grassland bird populations, and not become population sinks.
Striking the balance between these two goals can be difficult, and requires a long-term commitment to thoughtful, adaptative and creative management approaches. This is especially true when a grassland’s primary use is commercial hay production, or if hay production is the only feasible way that an individual or organization can facilitate management. It has become common practice to simply delay the initial mowing of grasslands in order to provide enough time for grasslands birds to fledge their young, but delayed mowing alone is often not enough to ensure the long-term viability of a grassland community. The annual delaying of mowing will eventually (and sometimes quickly) lead to the colonization of unwanted vegetation that results in the grassland becoming unusable to the species that the delays are intended to conserve. And from a financial perspective, delaying mowing can result in a less attractive crop that may lead to a farmer avoiding or abandoning such arrangements. While an ultimate solution to this issue has yet to be developed, the following considerations are offered to help find the appropriate balances for a variety of scenarios:
- Fully Delayed Field Mowing: An ideal situation for grassland bird nesting is to delay mowing through the entirety of the potential breeding season (generally May 01-August 15). However, this long delay can often be difficult to negotiate with a farmer who relies upon hay for income, and such delays also will result in an eventual shift in composition and structure toward woody and clonal vegetation. If such a delay is possible, fields should then be mown as frequently as possible after the first cut (up to the first frost) to help discourage the establishment of successional vegetation. Eventually, unwanted successional vegetation will establish, and so being prepared to treat this vegetation with herbicide will be important to maintaining the grassland in suitable condition for grassland birds. Annually monitoring the condition of the grassland is critical, and action should be taken as soon as woody vegetation (including Rubus and vines) and clonal forbs such as asters, goldenrods and milkweeds establish. There are a number of selective herbicides that will control these unwanted species without harming the desired grasses.
- Compromised Delayed Field Mowing: Delaying the first mowing until the end of the first week of July is a compromise that allows for the fledging of most grassland birds while better meeting farmer’s needs and keeping fields free of unwanted vegetation for longer. Most bobolinks will have fledged young by this time, and most eastern meadowlarks and savanna sparrows will have completed their first broods by this time. Some nesting mortality will occur under this scenario, but in most years, a delay to the end of the first week in July will result in enough fledging success to achieve positive population gains. Once the first mowing is complete, the field then should be mowed or hayed as frequently as possible (bobolinks will not renest after that initial mowing) until the season’s first frost in order to discourage the establishment of unwanted woody and clonal vegetation.
- Rotational Mowing: Another compromise strategy is to set aside a percentage of hayfields each year as refugia. This approach allows for unlimited mowing in one percentage of the fields in a complex, while requiring delayed mowing in the remaining percentage of fields. While not an ideal scenario for grassland birds, this approach will ensure that some percentage of habitat is retained each year in situations where a farmer may otherwise not be willing or able delay harvests across an entire grassland complex. Refugia units should be rotated through a field complex annually (a refugia patch should be placed in a different section of the complex each year) to reduce the establishment of unwanted vegetation. The percentage held out as refugia will be determined by what can be negotiated between the farmer and the landowner (or by how much a farmer is willing to delay harvest on their own land). Because grassland birds are area sensitive, refugia should always be established in the center of the largest fields.
- Spatially Delayed Mowing: In larger hayfields, another compromise strategy is to mow without restriction around the edges of fields, but delaying mowing in the interior of fields, where the majority of grassland birds occur.
- Grasslands versus Meadows: While it’s tempting to try to maximize the biodiversity of an individual patch, the reality is that the typical meadow forbs that are attractive to pollinators (asters, goldenrods and milkweeds) are the sign of a degraded grassland bird habitat. In short, the two values are not compatible on the same footprint. Meadow habitats are critically important, but if grasslands are being managed for grassland birds, then meadow habitats should be kept adjacent and complementary to the grassland habitat. Grassland birds typically avoid patches of these clonal species.
- Mowing Approaches:
- Mowing a field from the inside-out will continually push wildlife toward the outside of the field, leaving animals multiple escape routes from the mower. The more traditional mowing practice of mowing from the outside-to-the-center of the field essentially corrals wildlife into the center of the field, resulting in increased mortality on the mower’s final pass;
- Use a flush bar when mowing to alert wildlife of an oncoming mower;
- Raise the mower deck, especially for the initial mowing of the season. Even a few inches above standard can decrease wildlife mortality;
- Reduce mowing speed to allow wildlife to escape oncoming equipment;
- Avoid night mowing.
- Removing Material from Grasslands: Thatch build-up in cool season grasslands will:
- favor unwanted forbs over favorable grasses;
- result in later seasonal greening of fields, and;
- provide less favorable ground conditions for grassland birds.
Removing material is a natural outcome in fields managed for hay, but for other cool-season grassland situations, removing or burning off thatch every few years is ideal.
- Invasive Species: Invasive species such as reed canary grass and Canada thistle can transform a productive cool season grassland into a field that holds little value for either wildlife or agricultural resources. Prevention (ex. washing vehicles, quarantining livestock, avoiding feed that includes invasive propagules) and early detection/rapid response are always the preferred approaches when dealing with any invasive species. Established invasive occurrences require the use of herbicides for control, and there are a variety of herbicide products that are selective and won’t harm desirable grasses.
- Financial Assistance: Farmers who manage hayfields as financial resources, and individuals/organizations who rely upon farmers to manage their fields, may be eligible for financial assistance for income lost due to delayed mowing for conservation purposes. The Bobolink Project is one such Program. NRCS may also have programs to assist with cost-sharing.
- Making Sites Less Attractive to Grassland Birds: Sometimes the best way to benefit a population is to simply avoid creating population sinks within that population. Considering that most hayfields which are managed in ways that solely promote hay production are population sinks (attracting birds early in the breeding season, only to lose their breeding attempt when the field is mown later in the season), discouraging bird from nesting in the fields is important. This can best be achieved by high frequency mowing early in the breeding season. Under this scenario, grassland birds will still attempt to nest in the field, but will be driven off early enough in the breeding season to attempt breeding elsewhere.
Example Habitat Types
Hay fields, airfields, large cultural grasslands.
Frequency
Mowing should be conducted at least annually, especially during the growing season (in ways compatible with grassland bird nesting).
Relevance, Scale, and General Effort
Any grassland large enough to support breeding grassland birds should be considered a relevant conservation target for sustainable mowing practices.