Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Jun 21;11(1):12920.
doi: 10.1038/s41598-021-92437-z.

Monitoring abundance of aggregated animals (Florida manatees) using an unmanned aerial system (UAS)

Holly H Edwards  1 , Jeffrey A Hostetler  2   3 , Bradley M Stith  4 , Julien Martin  5
Affiliations

Monitoring abundance of aggregated animals (Florida manatees) using an unmanned aerial system (UAS)

Holly H Edwards et al. Sci Rep. .

Abstract

Imperfect detection is an important problem when counting wildlife, but new technologies such as unmanned aerial systems (UAS) can help overcome this obstacle. We used data collected by a UAS and a Bayesian closed capture-mark-recapture model to estimate abundance and distribution while accounting for imperfect detection of aggregated Florida manatees (Trichechus manatus latirostris) at thermal refuges to assess use of current and new warmwater sources in winter. Our UAS hovered for 10 min and recorded 4 K video over sites in Collier County, FL. Open-source software was used to create recapture histories for 10- and 6-min time periods. Mean estimates of probability of detection for 1-min intervals at each canal varied by survey and ranged between 0.05 and 0.92. Overall, detection probability for sites varied between 0.62 and 1.00 across surveys and length of video (6 and 10 min). Abundance varied by survey and location, and estimates indicated that distribution changed over time, with use of the novel source of warmwater increasing over time. The highest cumulative estimate occurred in the coldest winter, 2018 (N = 158, CI 141-190). Methods here reduced survey costs, increased safety and obtained rigorous abundance estimates at aggregation sites previously too difficult to monitor.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Locator map of manatee aggregation sites (Port of the Islands (POI), Wooten’s Pond, Big Cypress National Preserve and the manatee mitigation pools) in the Ten Thousand Islands of south Florida, USA, (b) POI Basin and location of the 12 canals and mitigation pools surveyed by the UAS. Map generated in ArcMap 10.3 (https://www.esri.com).
Figure 2
Figure 2
Water temperatures from the mouth of the Faka Union Canal south of the mitigation pools and estimates of manatee abundance during each survey in 2017, 2018 and 2019. Lines indicate water temperature: red line (2017), green dashed (2018) and blue dashed (2019). Shapes indicate the date of the survey and the abundance estimate: red circle (2017), green upside-down triangle (2018) and blue triangle (2019).
Figure 3
Figure 3
Example of manatees identified using the Kinovea software to create a sighting history for 1 min of video.
Figure 4
Figure 4
Estimates of the probability of detection for 1-min intervals for 6 min by site, date and min. Dots indicate means (point estimates) and lines the 95% credible intervals.
Figure 5
Figure 5
Estimates of the probability of detection for 1-min intervals for 10 min by site, date, and min. Dots indicate means (point estimates) and lines the 95% credible intervals.
Figure 6
Figure 6
Estimates of the cumulative probability of detecting a manatee using (a) 6 min and (b) 10 min of video, by site and visit. Symbols indicate means (point estimates) and lines 95% credible intervals. The numbers at the top of the graphs indicate the total number of minutes in each survey. Site “Mit Pools” are the mitigation pools and “BC” indicates Big Cypress.
Figure 7
Figure 7
Estimates of abundance (triangles and crosses) and maximum counts (circles and squares) by site and visit for 6 and 10 min of video. Symbols indicate means (point estimates) and lines 95% credible intervals. Site “Mit Pools” are the mitigation pools and “BC” indicates Big Cypress.
Figure 8
Figure 8
Total count (circles and squares) and abundance estimates (triangles and crosses) by visit, excluding Big Cypress. Symbols indicate means (point estimates) and lines 95% credible intervals.
See this image and copyright information in PMC

References

    1. Williams, B. K., Nichols, J. D. & Conroy, M. J. Analysis and Management of Animal Populations, Modeling, Estimation, and Decision Making (eds. Wood, J. M. & Tanner, G. W.) (Academic Press, 2002).
    1. Krause J, Ruxton GD. Living in Groups. Oxford Series in Ecology and Evolution. Oxford University Press; 2002.
    1. Riipi M, et al. Multiple benefits of gregariousness cover detectability costs in aposematic aggregations. Nature. 2001;413:512–514. doi: 10.1038/35097061. - DOI - PubMed
    1. Griffin AS, Savani RS, Hausmanis K, Lefebvre L. Mixed-species aggregations in birds: Zenaida doves, Zenaida aurita, respond to alarm call of carib grackles, Quiscalus lugubris. Anim. Behav. 2005;70:507–515. doi: 10.1016/j.anbehav.2004.11.023. - DOI
    1. Kunz, T. H. Roosting ecology of bats. In Ecology of Bats (ed. Kunz, T. H.) 1–55 (Springer, 1982).