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This Month in the Marsh - Sounds of the Marsh

Hi everyone, it’s me, Bri! The field season in the salt marshes of Maryland officially kicked off on May 22nd. Members of the Marshes for Tomorrow field crew worked diligently over the last two weeks conducting avian point count and playback surveys and deploying Autonomous Recording Units (ARUs). We saw notable species including Saltmarsh Sparrows, Clapper Rails, and Virginia Rails, and other common marsh species, such as Seaside Sparrows, Marsh Wrens, and Red-winged Blackbirds. 

In last month’s blog, I briefly described the survey techniques we would be using throughout the season. For this installment, I’ll touch on some of these techniques in greater detail.

Another beautiful day in the salt marsh - one of many we had this May!

What is a “point count” and “playback survey”?

“Point counts” are one of the most common methods of avian surveys used in wildlife studies. Avian point counts involve an observer recording birds at a single, predetermined location over a set period of time. The observer records birds that are either seen or heard within a certain distance from the predetermined point. Our team is following the SHARP protocol, which means we stand at a point for five minutes passively listening and observing all birds within a 100m circle. After the listening period, we transition to the “playback” survey where we use waterproof speakers and a mp3 player to broadcast a series of bird calls out across the marsh for seven minutes and listen for any responses. Response calls from live birds could indicate a behavioral message, such as a defensive individual signaling to a perceived intruder - “this is my territory - stay out!”. The broadcast includes vocalizations of Black Rails, Least Bitterns, Virginia Rails, King Rails, Clapper Rails, Common Gallinules, and Song Sparrows, which are considered focal marsh species for the SHARP protocol. At one of our survey points, we detected at least six individual Saltmarsh Sparrows, our star species!

What are “ARUs”?

Autonomous Recording Units, also known as “ARUs”, are a form of passive surveying techniques utilized in the marsh. Marsh birds, particularly species of rail, are difficult to see or hear due to their conspicuous nature and diurnal or nocturnal activity. ARUs are installed on a post at predetermined locations in order to increase the odds of capturing calls of these secretive birds from sunset to sunrise when we aren’t present. ARUs were deployed at our survey sites in late May, and will be checked and monitored until our last visit in July. We will use computer programs designed to analyze these audio recordings and determine what species were present in our marshes.

An older model of ARU (called the Song Meter SM3) that we are using this year is shown above.

One of the newer models of ARU we are using called the Song Meter Mini!

We will be heading back out into the marsh the second week of June for our next set of surveys, which will include mist-netting and bird banding to understand breeding populations of the Saltmarsh Sparrow. I am excited to continue to share what we see in the marsh on these visits. Please continue to follow along with the blog on the Marshes for Tomorrow website as well as Audubon Mid-Atlantic’s social media and newsletter for marsh updates! 

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