Using digital recordings to estimate occupancy and detection of marsh birds

Evaluating survey methods for the Yellow Rail: comparison of human surveys and autonomous recording units

Kiel Drake and Danica Hogan

Background Status of the Yellow Rail Federally listed as spp. of special concern in CanadaElusive species that is predominantly nocturnal Occupies habitats that are not covered by roadside surveys (i.e. not well-sampled by existing monitoring programs)Knowledge of breeding distribution, occurrence and abundance is incomplete

2YERA is a species of conservation concern in a variety of jurisdictions.Secretive species, vocalize predominantly at night, poor survey coverageSizable knowledge gaps include: range wide occurrence/abundance poorly understood; temporal and spatial variation in or N.Surveys for Yellow Rails

Human SurveysYERA occur in places that can be difficult to accessSurvey efforts need to be nocturnalIntensive survey protocol that employs call broadcast sampling and 2 visits to each stationObservers count individual calling males using auditory cues and determine (i.e., guess) distances to individuals

Autonomous Recording UnitsARUs: programmable, digital recorder that can enhance sampling opportunitiesStudies show that listeners of recordings detect similar to greater numbers of spp.3Study ObjectivesCompare estimates of occupancy, abundance, and detection probabilities that emanate from human surveys and ARU recordings.Gain a better understanding of seasonal and diurnal variation in calling behaviour.

?4Study Site: near Foam Lake, SK

5Study site is near the towns of Margo and Foam Lake, SK (i.e. 240 km ESE of Saskatoon).Survey stations occur at 500 m intervals in a systematic grid within marsh habitats; so the configuration of survey stations agrees with the recommendation by Conway (2011) to have survey stations 400m apart.~65% of the area of focus has potential to be emergent wetlands ranging from Class II-VI wetlands.

Methods: sampling

Human SurveysConducted point-count surveys 24 May-11 July between 22:00-03:00 hrs. (2011-2013)2-5 human surveys per station.Standardized marsh bird monitoring protocol: 10-min survey, call-broadcast sampling, and minute-by-minute tracking of individuals.

Autonomous Recording UnitsProgramed to record for 5-min at the beginning of each hour between 18:00-09:00 hrs.ARUs remained at each station for several days during deploymentRecordings were processed in a lab setting

Human surveys: nocturnal surveys following standardized marsh bird monitoring protocol; min-by-min tracking of individuals, with distance to calling birds estimated (guessed) by observers. Recognizing the inherent error in evaluating distance to aurally detected birds (Alldredges work), we simplified our field methods and assigned individuals to distance categories: 50m, 51-100m & >100m.ARUs: programmed to record 5-min intervals at the beginning of each hour (18:00-09:00 h); remained at stations for a few to several days at a time; recordings processed in the lab. ARUs cover an unknown survey radius that is smaller than that of humans that are not hearing impaired (internal microphone noise ranges ~32-40dB, so calls at sound intensity