Where are Merlins (Falco columbarius) nesting in Moorhead, and what factors affect their nest site selection?

MaryJo Nelson, Hiba Chaudhry, Sierra Vilmo, Elise Bakke, Dr. Chris Merkord

Biosciences Department, Minnesota State University Moorhead, 1104 7th Avenue South, Moorhead, MN 56563 USA

A female Merlin keeping a watchful eye. The male

is perched a couple meters below her in the same tree.

Photo: MaryJo Nelson, April 2021

Abstract

Merlins (Falco columbarius) are a small falcon that have begun breeding in more urban areas in the Northern Great Plains over the last forty years, and I am curious about why this is happening. This spring, I will be conducting two different types of surveys, nest surveys to determine likely nest sites and playback surveys to determine presence of Merlins, in order to get an idea of where Merlins are nesting here in Moorhead, MN. I have two main goals in my analysis of the data I collect. The first will be to compare the data between the two types of survey to assess whether the winter nest surveys were useful in determining where Merlins actually chose to nest. The second will be to look for patterns in the environmental factors associated with the Merlin nest sites (i.e. tree type, neighborhood, presence of bird feeders, presence of open areas, etc.) in order to get an idea of Merlin preferences when it comes to nest site selection. Information gleaned from this analysis will guide us in the right direction in how we design future studies in order to begin answering the question of why Merlins are nesting in urban areas and what that might mean for the conservation of Merlins and other species.

Introduction

Merlins are a small falcon that prey mostly on mid-sized birds, as well as bats, rodents, and other small mammals. They hunt in open areas but appear to prefer more tree dense areas for their nest sites, and rather than build their own nests, they use abandoned nests built by crows and hawks. Merlins have been known to nest in both conifer and deciduous trees, as well as on the ground and in cliffs, though in the northern great plains they appear to have a preference for conifer trees in urban settings (Warkentin et al 2020). Merlins were quite rare in Minnesota 100 years ago when they were mainly found north of the border, but recently their breeding territory has been expanding south into the upper mid-west, helped by their claiming nests of other birds (Kondrad 2020). Many Merlin nests have been reported in Spruce trees in North Dakota (Konrad et al. 2020). While breeding season typically runs from March to July, local lore suggests that breeding Merlins begin to arrive back to the area as early as February.

Our ultimate goal for this spring is to find as many Merlin nest sites as possible and to create a database listing their locations as well as any relevant environmental factors. We expect to find most nest sites in conifer trees in older neighborhoods, where there is higher tree density, as well as along the river corridor, but having this concrete data will give us a better understanding of what Merlins look for in a nesting site and allow us to better guess where they will choose to nest in years to come.

Methods

Survey Area

• We wanted to focus in on Moorhead since it is smaller and there is less ground to cover.

• In order to make the project manageable in the given time frame, we further reduced our survey area.

  • We used PLSS quarter sections to determine the size and position of each quadrant.

  • We chose 12 quadrants in a checkerboard pattern that would encompass the different types of environments in Moorhead (e.g. old neighborhoods, shopping centers, new neighborhoods, industrial areas).

• We used ArcGIS online to create a map with a layer for quadrants as well as individual layers for the points we planned on adding later

• We used orange marks to show where we knew Merlins had already been sighted this season or in the past

Nest Surveys

• Merlins claim the nests of other birds as opposed to building their own

• Walk or drive every accessible part of each quadrant looking for any and all visible nests

• Use arcGIS to mark locations of all visible nests

  

  A known Merlin nest in a conifer tree west of Eventide

  Photo: MaryJo Nelson, April 2021

Playback Surveys

Survey Points:

• Each quadrant is roughly 800m x 800m

• Placed survey points 200m apart both east to west and north to south

  • Our speakers have a roughly 100m range and we didn’t want to have the points so close that we would be pulling in the same birds over and over

• Started in the furthest north west corner of each quadrant and placed points moving east, then row by row moving south

• Each row is offset of the row directly north of it by 50m

• For some quadrants, this was fairly straight forward. For others we had to get creative:

  • If the point landed somewhere that is inaccessible to the public, we moved it to the closest spot we could find withing a roughly 10 meter radius (20-30m if we were desperate)

  • If there was no public location available within radius of the point, then the point was omitted.

In the Field

1. Surveys are conducted in pairs in order to have more eyes and ears looking out for possible responses

2. Record start time and recording being used

3. While standing on a point, play Merlin call once in all directions (north, west, south, and east), then wait approximately 30 seconds to a minute for a response (Merlins tend to respond right away to a call)

4. Mark Presence or Absence

5. If Presence, note other pertinent information (e.g. auditory response, visual, male, female, pair, in flight, in tree, flight path, etc.)

   Technology used:

   • ArcGIS Field Maps - for moving to points and marking points of interest

   • Merlin Bird ID - has a library of bird calls, played Merlin bird calls through speaker for playback

   • JBL Clip 4 - small, rugged, weather resistant speaker with good audio range for performing playback

Elise performs playback with the JBL Clip 4 and the Merlin Bird ID app.

Photo: MaryJo Nelson, April 2021

Progress and Results

(We’re finding things!)

A male perches in a deciduous tree west of Eventide

Photo: MaryJo Nelson, April 2021

So far we have surveyed quadrants 06, 08, 09, 11, and 12. Below is a map of all our findings thus far.

• Blue marks = nest sighted, but no evidence of Merlin activity

• Orange marks = Merlin sighted

• Green star = propable or confirmed nest

Nest Surveys

Due to busy schedules and lack of research assistants earlier in the year, we struggled to find time to do nest surveys. We only ended up surveying 2 quadrants for nests (09 and 11), with very few possible nests sighted, and we found it nearly impossible to see nests in conifer trees, where we predicted Merlins would most likely choose to nest. We have now done playback surveys at both quadrant 09 and quadrant 11 and have received no response near the nests that we marked during nest surveys.

Playback surveys

• With four field technicians, we are currently doing 4 to 6 surveys per week!

• We have 2-2.5 hours scheduled per survey, however we have found that we struggle to finish a quadrant in this time

  • When we receive no response, we spend roughly 5-7 minutes at each point (including travel time between points). At about 20 points per quadrant, that’s over 2 hours of survey time.

  • However when we do receive a response, we typically end up spending 15-30 minutes in that area, tracking and monitoring the bird(s) and looking for the nest, making it harder to finish the survey within the time frame.

• So far we have found at least one potential or confirmed nest in each quadrant

Patterns we’ve noticed so far:

• Every potential nest so far has been in a conifer tree, usually toward the very top within 1 meter of the highest point

• Often, the female is in the nest tree and the male is “standing guard” in a nearby deciduous tree

• Interestingly, most potential nest have been in louder/busier parts of the neighborhood

  • All have been on, or within 50 meters of a busy street

  • In really quiet neighborhoods, we rarely get a response

• We also haven’t received any responses near the river corridor, where we were expecting to see more activity

Nest Visits

• So far we have revisited 5 out of the 7 potential nest sites, and have confirmed 3 nests with a Merlin pair present

• At the two unconfirmed nest sites:

  • Nests were definitely seen, but no Merlin activity was noted at the time of the visit

  • However, both of these sites had an active pair present at the time of the initial sighting during playback surveys, so these are still promising nest sites!

Here you can see the nest on the left side of the frame and the female on the right. Photo taken during a nest visit to suspected nest next to Valley Premiere Bank in south Moorhead.

Photo: MaryJo Nelson, April 2021

What’s Next?

1. Finish Playback Surveys

   • We have only completed 5 of the 12 survey quadrants.

   • We need to survey the remaining quadrants

   • Time permitting, we may like to survey each quadrant a second time at a different time of day from when it was previously done.

2. Nest Visits

   • Visit all suspected nest trees to confirm presence of Merlin pair and nest.

   • Record pertinent information about nest site and environmental factors (e.g. tree species, tree height, nest height, nest direction, field nearby, bird feeder presence, etc.)

   • Periodically visit each confirmed nest tree to monitor Merlin behavior and progress/fitness of young (fledglings are expected to hatch in June)

3. Data Analysis

   • Compare environmental and tree data collected for each confirmed nest to assess for patterns in Merlin nest site preference

   • Compare environmental data of where Presence was recorded vs. where absence was recorded to develop a better understanding of where Merlins choose to nest vs. where they choose not to nest.

Identifying Merlins

• Click here for a great resource about identifying Merlins!

• Click here to see a Merlin calling!

Photo: © Joel Trick | Macaulay Library

A female (top) and a male (bottom) showing off their different colors.

Photos: MaryJo Nelson, April 2021

Attempting to capture images of Merlins on a phone and through binoculars is NOT EASY!

Photo: Elise Bakke, April 2021

If you see a Merlin around town, we would love to hear about it!

• Please email myself or Dr. Merkord with the date and location that you saw it, and we will add it to our database

  • maryjo.nelson@go.minnesota.edu

  • chris.merkord@mnstate.edu

• This will help us to know where more nests might be so that we can create the most extensive database possible of Merlin breeding sites in the area.

Thank you for being engaged and learning more about this awesome project!

References

• Konrad PM, Shaffer JA, and Igl, LD. 2020. The effects of management practices on grassland birds—Merlin (Falco columbarius). In:Johnson, DH, Igl LD, Shaffer JA, and DeLong, JP, editors. The effects of management practices on grassland birds: US Geol Surv Prof Pap 1842-R. 12 p. https://doi.org/10.3133/pp1842R

• Merlin. Mnbirdatlas.org. [accessed 2021 Apr 20]. https://mnbirdatlas.org/species/merlin/

• Warkentin IG, Sodhi NS, Espie RHM, Poole AF, Oliphant LW, James PC. Merlin (Falco columbarius). Birds of the World. 2020 [accessed 2021 Apr 20]. https://birdsoftheworld.org/bow/species/merlin/cur/introduction. doi:10.2173/bow.merlin.01