January 24, 2019

Ghosts of the Grassland: Farmland Raptor Research

Northern Harrier flying over local grasslands

Grassland is one of the fastest disappearing habitats in the United States, and as North America is one of the last sites for extensive temperate grasslands in the world, this truism is tragic not only for our aesthetic fulfillment but also for the future of grassland-dependent wildlife species. Habitat availability and quality are now a routinely referenced threat to the health of animal populations across the globe. Grassland birds and pollinators in particular have conservationists concerned and desperately trying to raise more awareness about the implications this loss could have on our ecosystems.

In Pennsylvania, cropland decreased by 43% between 1940 and 2012, and pasture areas have diminished by a surprisingly high 88% during an even smaller time frame. Both of these are critical habitat for a variety of grassland birds, and are likely the primary cause for declines across an array of species. Other related causes could be the shift to larger farms resulting in greater pesticide use and consequently affecting the entire grassland food web, shifts from pasture to row crops which reduce vegetative cover in the winter, and frequent hay cutting which endangers ground-nesting birds during reproduction.

Most related studies have focused on songbirds, however, the impact of this habitat loss on raptors has rarely been assessed. Our Director of Conservation Science Dr. Laurie Goodrich has recently co-authored a paper investigating the presence of two grassland or more commonly referred to as “farmland” raptors in Pennsylvania, the northern harrier (threatened) and the short-eared owl (endangered). Dr. Goodrich and lead author Jerry Griffith wanted to learn which “classes” of grassland are used most by these two species, especially during the non-breeding season. Across the scope of ecological studies we are realizing that we must assess a species’ annual cycle to truly understand their life history, and therefore detect threats proactively. Hawk Mountain’s research on farmland raptors aims to contribute to this needed body of holistic knowledge. 

Dr. Goodrich and colleagues examined the relationship between land cover and the presence of both birds during breeding and wintering seasons. They used citizen science databases (Ebird and the PA Farmland Raptor Project of Hawk Mountain Sanctuary) to overlay sightings of both species (598 sightings of harriers, 129 for short-eared owls) with land cover types to see which habitats were used most frequently and when. Two important conclusions surfaced: expansive open habitat and minimal human development were important factors dictating which areas could support the most birds. Generally speaking, when ecosystems are fragmented they become less functional and with human development comes a slew of potential risks to ground-nesting birds such as predation by feral cats, mowing, and pesticide use, to name a few.

tertiary farmland food web
This study demonstrates the importance of maintaining grassland habitats that are as unbroken and uninterrupted as possible. Harriers and owls are natural rodent control for farmlands and because they are high up in the food chain, they provide helpful indications of how an ecosystem is faring. If top predators begin to show signs of struggle, there are likely issues elsewhere in the levels of primary and secondary production

Next research steps may include deploying transmitters on farmland raptors to better understand how habitat use by these species vary between seasons and across spans of time. This study also identified several locations that were used as winter roost sites by multiple birds, and ideally either the sites themselves or the associated habitat types could be prioritized as critical wintering habitat. For this to happen, convincing information will need to be shared with state agencies and land conservancies.

Farmland raptors are an integral component of the grassland ecosystem, and in Pennsylvania where we have a large proportion of agricultural land, the quality of open space for wildlife should be a state-wide priority given the consequences that may arise if ecosystem dynamics are ignored. No matter our background, we can all help spread awareness about the value of Pennsylvania’s remaining grasslands through participation in citizen science projects, financial support of research endeavors, or by simply spreading the word and demonstrating respect for these irreplaceable raptors whenever possible. Let’s do our part to ensure that the gray ghosts do not become true ghosts, leaving our fields haunted by the memory of what once was.

Dr. Goodrich would like to acknowledge Jerry Griffith, PA Farmland Raptor Project coordinator Katie Andrews, and participating farmers for all their hard work not only for this study, but for the future of farmland raptors. 

Click here to learn more about the PA Farmland Raptor Project. Click here to download Dr. Laurie Goodrich's paper, “Land Cover and Farmland Raptor Distribution in Pennsylvania.”