Population monitoring

 

The historical range of the snail kite once covered over 4000 km2 (2480 mi2) in Florida,

including the panhandle region (Davis and Ogden 1994, Reichert et al. 2015). Since the

mid-1900s it has been restricted mainly to the watersheds of the Everglades, Lake

Okeechobee, Loxahatchee Slough, Kissimmee River Valley (KRV), and the Upper St. Johns

River of the central and southern peninsula. After several decades of landscape

fragmentation and hydroscape alteration, the kite population is now confined to a

fragmented network of freshwater wetlands that remain within its historical range,

and the viability of the population rests entirely on the conditions and dynamics of

these wetland fragments (Bennetts and Kitchens 1997a, Martin 2007). The snail kite

is unique in that it is the only avian species that occurs throughout the central and

south Florida ecosystem and whose population in the U.S. is restricted to freshwater

wetlands in this region. The dependence of the snail kite on these habitats makes it

an excellent barometer of the success of the restoration efforts currently underway

(Kitchens et al. 2002) (e.g., USFWS Multi-Species Transition Strategy for Water

Conservation Area 3A, 2010). We track short-term and long-term changes in the

snail kite population to understand how water management, human activities,

and natural events influence its recovery.

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Trends

Trends from our demographic studies revealed a drastic decline in the snail kite

population in Florida between 2000-2008, with the population essentially halving from

2000 to 2002 and again from 2006 to 2008 (Martin et al. 2007 and Reichert et al. 2016).

Range-wide population estimates significantly increased from 2010 to 2013. This

increase in population size was driven primarily by large increases in snail kite

reproduction in the KRV and Lake Okeechobee (Reichert et al. 2016), which have been

inked to increased food availability due to the invasion of an exotic apple snail

(Pomacea maculata) (Cattau et al. 2016). However, snail kite abundance has continued

to decline in the southern parts of its' range (Everglades and Loxahatchee Slough

watersheds), a region of wetlands designated as 'critical habitat' (Reichert et al. 2016).

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Nesting

Nest monitoring of kites is essential for three reasons. First, it provides critical information for Criterion 5 of the USFWS recovery plan for Snail Kites. Second, reproduction is directly linked to population change in snail kites and is a demographic rate that is amenable to
site-specific management. Third, banding fledglings at nests provides a low-cost, value-added approach for marking snail kites (an important element for reliable population size estimation; Williams et al. 2002). Focusing banding on juveniles has the added benefits of knowing the exact age of individually banded kites and obtaining a large sample size of marked juveniles, which show lower, and more variable, survival rates than adults (Martin et al. 2007 and Reichert et al. 2010). Understanding effects of age structure is also important for population dynamics, and has been shown to be highly relevant to interpretation of reproduction (Reichert et al. 2012), survival (Reichert et al. 2010), and regional trends in population size of snail kites (Reichert et al. 2016).

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Survival

We use information on individually marked snail kites to estimate survival. We focus on banding juveniles as it has the added benefit of knowing the exact age of individually banded kites and obtaining a large sample size of marked juveniles. Risk of mortality is often highest up to five months post fledging when young birds are learning to foraging (Bennetts and Kitchens 1997). Adult survival in snail kites is relatively high and stable compared to first-year birds, but is negatively affected by drought conditions (Bennetts and Kitchens 1997, Martin et al. 2006, and Reichert et al. 2010). 

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References

Bennetts, R. E., and W. M. Kitchens. 1997. The demography and movements of snail kites in Florida. Gainesville, FL.

 

Cattau, C. E., R. J. Fletcher, B. E. Reichert, and W. M. Kitchens. 2016. Counteracting effects of a non-native prey on the demography of a native predator culminate in positive population growth. Ecological Applications 26:1952–1968.

 

Davis, S. M., and J. C. Ogden. 1997. Everglades: the ecosystem and its restoration. Page (S. M. Davis and J. C. Ogden, Eds.). St. Lucie Press, Boca Raton, Florida.

 

Kitchens, W., R. Bennetts, and D. DeAngelis. 2002. Linkages between the snail kite population and wetland dynamics in a highly fragmented South Florida hydroscape. Pages 183–203in J. W. Porter and K. G. Porter, editors.The everglades, Florida bay, and coral reefs of the Florida keys, An ecosystem sourcebook. CRC Press, Boca Raton.

 

Martin, J., W. Kitchens, C. Cattau, and M. Oli. 2008. Relative importance of natural disturbances and habitat degradation on snail kite population dynamics. Endangered Species Research 6:25–39.

 

Martin, J., W. Kitchens, and J. Hines. 2007a. Natal location influences movement and survival of a spatially structured population of snail kites. Oecologia 153:291–301.

 

Martin, J., W. M. Kitchens, and J. E. Hines. 2007b. Importance of well-designed monitoring programs for the conservation of endangered species: case study of the snail kite. Conservation Biology 21:472–81.

 

Martin, J., J. D. Nichols, W. M. Kitchens, and J. E. Hines. 2006. Multiscale patterns of movement in fragmented landscapes and consequences on demography of the snail kite in Florida. The Journal of Animal Ecology 75:527–39.

 

Reichert, B. E., C. E. Cattau, R. J. Fletcher, W. L. Kendall, and W. M. Kitchens. 2012. Extreme weather and experience influence reproduction in an endangered bird. Ecology 93:2580–2589.

 

Reichert, B. E., C. E. Cattau, R. J. Fletcher Jr, P. W. Sykes Jr, J. A. Rodgers Jr, and R. E. Bennetts. 2015. Snail Kite (Rostrhamus sociabilis). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.

 

Reichert, B. E., W. L. Kendall, R. J. Fletcher Jr., and W. M. Kitchens. 2016. Spatio-temporal variation in age structure and abundance of the endangered snail kite: pooling across regions masks a declining and aging population. PLoS ONE 11:e0162690.

 

Reichert, B. E., J. Martin, W. L. Kendall, C. E. Cattau, and W. M. Kitchens. 2010. Interactive effects of senescence and natural disturbance on the annual survival probabilities of snail kites. Oikos 119:972–979.

 

U.S. Fish and Wildlife Service. 2010. USFWS Multi-species tranistion strategy for Water Conservation Area 3A. Vero Beach, FL.

 

Williams, B. K., J. D. Nichols, and M. J. Conroy. 2002. Analysis and management of animal populations: modeling, estimation, and decision Making. Academic Press.

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