Lack of standardization in the use of road counts for surveying raptors

Abstract

Examination of population trends for raptors is a research priority, especially given recent concern for their conservation status. Road counts—in which raptors are counted from a motorized vehicle moving along the ground—might be an effective method to expand the monitoring of raptor populations and estimation of trends. Here, we review past methods used to perform road counts of raptors and present revised recommendations to aid collaboration, data transfer, and interpretation of results across monitoring programs. We performed a standardized keyword search of online literature databases to obtain 148 past road count studies. The number of studies employing road counts increased per year since the 1970s. Most of these studies occurred in North America. The times of day during which road counts were conducted ranged from sunrise to sunset, and maximum speeds ranged from 10 to 113 km hr–1. The number of observers ranged from 1 (the driver) to 5. Most (93) of the studies used unlimited-width transects and fixed-width transects ranging from 0.02 to 2.50 km wide. Sixteen percent of studies calculated or corrected for the probability of detection. Such broad variation in the methodology used during road counts, coupled with infrequent correction for detection, hampers the interpretation of results across road survey programs. We suggest that road count practitioners should emphasize the collection of data, such as speed, number of observers, and distance to observed raptors, which would allow for the calculation of detection-corrected estimates. Such correction would likely improve trend estimation. Recent technology, including mobile apps, allows researchers to collect such data relatively easily, conducting their own studies while contributing to a broader raptor monitoring initiative. Road counts will likely become more useful as statistical analysis of road count data improves and researchers pool their data in a global effort to monitor raptors.

Yearly temperature fluctuations and survey speed influence road counts of wintering raptors

“…Road count data have been used to inform policy and red-listing decisions (Ogada et al 2016, BirdLife International 2019, and can be used to monitor species across large areas. To realize the full potential of road counts, practitioners must develop enhanced infrastructure (including mobile apps and online databases), methodology, sampling design and analyses (McClure et al 2021).…”

“…Despite the efficacy of road counts for surveying raptors, analytical methods to account for variation in survey effort are sorely needed and underdeveloped (McClure et al 2021). For example, a recent review of 148 road count studies revealed great variation in reported speed travelled during road surveysranging from 10 to 113 km/h (McClure et al 2021). Of these studies, only two examined effects of survey speed on the number of birds counted.…”

Seasonal Abundance and Habitat Associations of American Kestrels on the Southern High Plains of Texas

“…Data Collection. We used road transect surveys as our sampling method because of its practicality in an agriculture- and grassland-dominated landscape with abundant rural roads across a mosaic of private land ownerships (Andersen 2007, McClure et al 2021a). Two observers experienced in kestrel identification conducted monthly surveys on a 141-km-long by 1.6-km-wide (half-width of 800 m) road transect from December 2012 through November 2014 (Linner 2014).…”

Commentary: the Past, Present, and Future of the Global Raptor Impact Network

“…The GRIN mobile app also maintains the road survey functionality of the ARDB mobile app. Road surveys are especially useful for monitoring raptors across large areas with open vegetation Mosher 1981, 1987), yet technological infrastructure and analytical tools for such surveys have been, until recently, underdeveloped (McClure et al 2021a). The GRIN mobile app allows recording of start and end times of surveys, georeferencing routes and observations DECEMBER 2021 (Fig.…”

“…The methodology we have developed for scoping reviews will be applied to each raptor species and to specific research topics. For example, the review conducted by McClure et al (2021a) of road count methodology in raptor surveys can be updated periodically with tables maintained online.…”