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San Antonio River Basin Report Card

2020

Report Card Summary

2020
San Antonio River Basin Report Card Summary
The overall grade for the 2020 San Antonio River Basin Report Card is B. This grade is the average of twelve individual indicator grades, which are explained in greater detail below.
66.2
Growth of Whooping Crane Population
Growth of Whooping Crane Population
How is this being measured?
Explanation of the grade
Key findings

A+Growth of Whooping Crane Population

While all the metrics in the San Antonio River Basin Report Card have overlapping correlation to the safe, clean, enjoyable creeks and rivers aspects of the River Authority’s mission, the Whooping Crane Population grade is primarily related to the clean aspect.

Whooping Crane

The Whooping Crane is one of the rarest bird species in North America. It is also the largest; standing tall at up to five feet with a wingspan of up to 7.5 feet. The Aransas-Wood Buffalo Population (AWBP) is the only remaining wild population of Whooping Cranes. This population of Whooping Cranes migrates from Canada, where it spends the summers, to Aransas National Wildlife Refuge, where it winters in the bays and estuaries near San Antonio Bay. The San Antonio River confluences with the Guadalupe River a little more than 10 miles from the bay where the freshwater inflows of both rivers are important contributors to the health of the bay and estuary system.

Once reduced to near extinction, with as few as 15 cranes in 1941, recovery efforts have expanded this population considerably in recent years. The River Authority engages with numerous partners at the state, local, and federal level to foster understanding that healthy waters upstream, contributes to healthy waters downstream and into the bay and estuary system where the Whooping Cranes rely on a clean habitat for food.

The River Authority is using this metric for the San Antonio River Basin Report Card because a healthy population of Whooping Cranes can be considered an indicator for a healthy bay and estuary system in San Antonio Bay. Whooping Crane survival depends on human choices throughout the San Antonio River Basin from the City of San Antonio to San Antonio Bay. As the United States Geological Survey (USGS) points out about Whooping Crane restoration, “Since humans contributed to the decline of the Whooping Crane, many people now feel that we have a moral duty to help this magnificent bird. Our natural heritage of biological diversity – all of the species of plants and animals – is a precious resource.  Our future quality of life depends on how we take care of our natural inheritance.”

How is this being measured?

According to the United States Fish and Wildlife Service (FWS) Whooping Crane Recovery Plan, the “ultimate goal is to recover the Whooping Crane and remove it from the lists of Threatened and Endangered Species.” However, the plan also makes clear in several locations that it is “not feasible to establish well-defined objectives and criteria for delisting at this time.” Challenges to establishing delisting objectives and criteria include:

  • The extremely endangered status and the slow reproductive rate of the species which impacts the length of time expected to reach downlisting goals;
  • Information gaps in the current scientific knowledge of the species, such as a highly confident understanding of a minimum population size needed to ensure species survival; and
  • Difficulty predicting the environmental conditions and threats to the species as new threats are expected to manifest over time and will have to be overcome before downlisting occurs.

Given the FWS does not yet have well-defined objectives and criteria, there isn’t an existing measurement to grade against for this report card. Therefore, for this metric, we are creating a grade for Whooping Crane population using annual bird counts. FWS completes aerial surveys annually to estimate the abundance of Whooping Cranes in the AWBP. The San Antonio River Basin Report Card will use the annual FWS aerial surveys to score Whooping Crane counts from the past year (Winter 2019-2020) against the annual average counts from the four previous winter survey years (2015-16, 2016-2017, 2017-2018, and 2018-2019).

Whooping Crane

Essentially, the grade is a trend analysis with the basic assumption for the grade being that maintaining and/or increasing Whooping Crane populations year after year is positive (i.e. resulting in a higher grade) and decreasing populations is negative (i.e. resulting in a lower grade). Being a trend analysis, it is possible that this grade may produce scores above 100 or below 0. Scores above 100 will be shown as an “A+” on the report card dashboard and a score below 0 will be shown as a “F.” The actual numeric value will be used in the averaging of all metrics to produce the overall basin grade.

Please note, the 2021 San Antonio River Basin Report Card and beyond will use the five previous winter season FWS aerial surveys rather than four as we are in this year’s report card. The FWS changed the aerial survey process during the Winter 2015-2016 count so we decided that using data prior to this counting methodology change would be inappropriate. The FWS aerial count methodology changes included using a different type of aircraft and conducting the count later during the winter season. The change from a Cessna aircraft, which was used in the past, to a Kodiak aircraft was made because the Kodiak has better visibility than the Cessna, which improves survey data and results in a more accurate population estimate. The FWS moved the aerial count from December to now taking place in either February or March because the “abundance estimate from December was likely not capturing the entire whooping crane population, given that some birds had not completed migration yet.”

Explanation of the grade

Winter Whooping Crane county 2015-16 Winter Whooping Crane county 2016-17 Winter Whooping Crane county 2017-18 Winter Whooping Crane county 2018-19 4-year average of winter counts Winter Whooping Crane county 2019-20 Score Grade
463 489 505 504 490 506 103 A+

 

Key findings

The annual winter Whooping Crane counts are trending up over the last five years of winter counts, which is positive. According to the International Crane Foundation’s Whooping Crane information, the greatest threat to Whooping Crane populations is “Loss or deterioration of critical wetland habitat – including reduced fresh water on wintering grounds in Texas, sea-level rise, low genetic diversity, power line collisions, predation, disturbance at nest sites, and illegal shootings.”

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