Annual Aerial Surveys Research Articles

TIMING OF REDD CONSTRUCTION BY FALL CHINOOK SALMON IN THE HANFORD REACH OF THE COLUMBIA RIVER

ABSTRACTSpawning habits of fall Chinook salmon in the Hanford Reach of the Columbia River have been documented with annual aerial surveys since 1948. We developed a series of models analysing these data, exploring the influence of environmental factors on the timing of redd construction. These models included a logistic regression and a dynamic modelling approach, with combinations of day of year (as a surrogate for environmental cues such as day length), water temperature and discharge as potential explanatory factors. Results of these analyses indicate that day of year was the strongest predictor of the timing of redd construction, but with significant modifying effects of water temperature and discharge. The dynamic modelling approach provides substantial advantages over a traditional logistic regression, including (1) the ability to treat data collected at non‐synchronous time intervals in a consistent fashion and (2) the ability to easily implement complex functions (e.g., threshold responses) relating behaviour to environmental cues. Evaluation of the series as a whole indicates that the median date of redd construction has increased over time, from approximately day 299 in 1950 to day 307 in 2010, as has the temperature on Oct 1 (16.3 °C–18.1 °C). The degree to which these changes are caused by climate change or dam operations is uncertain, however. Copyright © 2013 John Wiley & Sons, Ltd.

The status of grey seals in Britain

Grey seal pup production in Scotland was estimated through annual aerial surveys of the main grey seal breeding colonies. Between 3 and 7 counts of pups were obtained for each colony at intervals through the course of the breeding season. Pup production for individual colonies was estimated from the series of counts using a maximum likelihood model. At 3 colonies, 2 in England, annual pup production was estimated using ground counts. Between the early 1960s and the early 1990s, grey seal pup production progressively increased. At colonies in the Inner and Outer Hebrides, production appeared to stabilize during the 1990s and has remained so. Pup production at colonies in Orkney and in the North Sea has continued to increase but in recent years the rate of increase has declined. This may imply that the UK grey seal population is reaching some limit to its size. The observed changes in pup production imply that some density dependent factors are affecting the British grey seal population. Changes in either juvenile survival and/or female fecundity are the most likely options. Without knowing which of these, or what combination of these factors, is operating, estimating total population size is complicated.

Short communication: Abundance, distribution and population trends of Nile crocodile (<i>Crocodylus niloticus</i>) in Gonarezhou National Park, Zimbabwe

The Nile crocodile ( Crocodylus niloticus ) is an iconic or keystone species in many aquatic ecosystems. In order to understand the abundance, distribution, and population trends of Nile crocodiles in Gonarezhou National Park (GNP), southeastern Zimbabwe, we carried out 4 annual aerial surveys, using a Super Cub aircraft, along 3 major rivers, namely, Save, Runde and Mwenezi, between 2008 and 2011. Our results show that Runde River was characterised by a significant increase in Nile crocodile abundance whereas both Save and Mwenezi rivers were characterised by non-significant increases in Nile crocodile abundance. Overall, we recorded a significant increase in total Nile crocodile population in the three major rivers of the GNP. The non-significant increase in Nile crocodiles in the Mwenezi and Save rivers was likely due to habitat loss, through siltation of large pools, and conflicts with humans, among other factors. We suggest that GNP management should consider halting crocodile egg collection in rivers with low crocodile populations and continuously monitor the crocodile population in the park. Keywords: Abundance, aerial survey, Nile crocodile, population, river, Zimbabwe

A comparison of multiple indicator kriging and area-to-point Poisson kriging for mapping patterns of herbivore species abundance in Kruger National Park, South Africa

Kruger National Park (KNP), South Africa, provides protected habitats for the unique animals of the African savannah. For the past 40 years, annual aerial surveys of herbivores have been conducted to aid management decisions based on (1) the spatial distribution of species throughout the park and (2) total species populations in a year. The surveys are extremely time consuming and costly. For many years, the whole park was surveyed, but in 1998 a transect survey approach was adopted. This is cheaper and less time consuming but leaves gaps in the data spatially. Also the distance method currently employed by the park only gives estimates of total species populations but not their spatial distribution. We compare the ability of multiple indicator kriging and area-to-point Poisson kriging to accurately map species distribution in the park. A leave-one-out cross-validation approach indicates that multiple indicator kriging makes poor estimates of the number of animals, particularly the few large counts, as the indicator variograms for such high thresholds are pure nugget. Poisson kriging was applied to the prediction of two types of abundance data: spatial density and proportion of a given species. Both Poisson approaches had standardized mean absolute errors (St. MAEs) of animal counts at least an order of magnitude lower than multiple indicator kriging. The spatial density, Poisson approach (1), gave the lowest St. MAEs for the most abundant species and the proportion, Poisson approach (2), did for the least abundant species. Incorporating environmental data into Poisson approach (2) further reduced St. MAEs.

Physical–biological interactions in a subarctic estuary: How do environmental and physical factors impact the movement and survival of beluga whales in Cook Inlet, Alaska?

The annual abundance population estimates of the endangered beluga whales in Cook Inlet (CI), Alaska, have indicated a decline in the population over the past decades and no convincing explanation has been offered so far for this trend. Satellite tracking data of about 20 Cook Inlet beluga whales (CIBW) over some 5-year period, as well as annual population counts and stranding reports were compared with environmental observations. The seasonal movements of the belugas within CI appear to be affected by variations in water temperature, ice coverage and most significantly, by river discharge. Statistically significant correlations were found between the seasonal movements of the CIBW and the timing of peak flows at different rivers. Interannual variations of the CIBW movements were found to relate to year-to-year variations in water temperature and the time of ice melt/freezing; thus, in warmer years the CIBW will stay in the upper inlet longer, before dispersing to the mid and lower CI in winter. Both, the population of the beluga and stranding numbers show a 3–4-year cycle of interannual variations resembling the Pacific Decadal Oscillation (PDO) index, though the exact mechanism in which large-scale climate variations impact the CIBW habitat is not clear yet. The analysis suggests that the method of estimating the CIBW population from annual aerial surveys needs further evaluation, since interannual changes in the spatial distribution of CIBW preferred locations may have a confounding effect on estimates of population abundance.

Distributional niche of relatively rare sable antelope in a South African savanna: habitat versus biotic relationships

The geographic distribution of a species is governed by climatic conditions, topography, resources and habitat structure determining the fundamental niche, while the local distribution expressed via home range occupation may be compressed by biotic interactions with competitors and predators, restricting the realised niche. Biotic influences could be especially important for relatively rare species. We investigated how rainfall, geology, land type and abundance of other ungulate species serving as competitors or prey for predators contributed to the patchy distribution of sable antelope herds within Kruger National Park. Data were provided by annual aerial surveys of ungulate populations conducted between 1978 and 1988. Sable herds were more commonly present on granitic and sandstone substrates than on more fertile basalt. They occurred both in the moist south‐west and dry north of the park. They were most abundant in sour bushveld and mopane savanna woodland, and mostly absent from knob thorn‐marula parkland. The presence of sable was negatively associated with high concentrations of impala and wildebeest, less consistently related to the abundance of zebra, and positively associated with the occurrence of buffalo herds. Best supported models included the separate effects of the most abundant grazers along with land type. Interspecific relationships seemed more consistent with vulnerability to predation as the underlying mechanism restricting the distribution of sable herds than with competitive displacement. Sable favoured land types distinct from those where wildebeest, the most preferred prey of lions, and impala, numerically the most important resident prey species, were most abundant. Hence the risk of predation, associated with habitat conditions where abundant prey species are most concentrated, can exert an overriding influence on the distribution of rarer species in terms of their home range occupation.

Soil properties affect pinyon pine – juniper response to drought

ABSTRACTSince the late 1990s, drought‐driven dieback has affected more than a million hectares of pinyon pine‐juniper woodlands in the southwestern USA. Analysis of annual aerial surveys by the US Forest Service and soil survey data shows that most of the mortality occurred between 2003 and 2004 and that 70% was restricted to soils mapped as having available water storage capacities (Ac) <100 mm. We conducted a more refined analysis and found that asAcincreased in increments of 50 mm up to 300 mm, the distribution of areas with observed mortality decreased exponentially from 42% to 3% (n = 6 classes,r2 = 0.93). We used this information in a process‐based stand growth model, physiological principles predicting growth, to assess year to year variation in gross photosynthesis between 1985 and 2005 with climatic data at monthly intervals from four weather stations where pinyon‐juniper woodlands were confirmed by satellite imagery. A sensitivity analysis identified sustained periods of drought and supported field observations that once canopy leaf area approaches a maximum value, the majority of mortality should be restricted to soils withAcvalues <100 mm. Additional analyses indicated that differences in soil texture played a small part (<10%) in the variation of gross photosynthesis and that consecutive years of drought may have a cumulative effect on pinyon pine vulnerability to bark beetle attack. Disturbances reducing canopy leaf area index should result in less pine mortality in the future, although conversion to shrub and grassland may occur if climate conditions continue to become less favorable. Copyright © 2012 John Wiley & Sons, Ltd.

Changes in Elk Distribution and Group Sizes after Wolf Restoration

Abstract Changes in ungulate distribution can alter competitive interactions, plant communities, risks of zoonotic disease transmission, and availability of animals for harvest. We used annual aerial survey data for northern Yellowstone elk in Montana and Wyoming, USA to evaluate factors influencing distribution and group sizes during 1987–2009 in four sectors of elk winter range corresponding to river watersheds with different minimum elevations and snowpacks. Our best logistic regression model suggested the proportion of elk occupying the upper elevation sector decreased following wolf restoration and increased snowpack. The proportion of elk occupying the lower elevation sector increased following wolf restoration and as snowpack increased at higher elevations. Linear regression suggested group sizes increased in the lower elevation sector after wolves were restored. Concurrent demographic and movement studies suggest these changes resulted primarily from the attrition of elk from high snow areas in Ye...

Influences of Salinity and Light Availability on Abundance and Distribution of Tidal Freshwater and Oligohaline Submersed Aquatic Vegetation

Submersed aquatic vegetation (SAV) communities have undergone declines worldwide, exposing them to invasions from non-native species. Over the past decade, the invasive species Hydrilla verticillata has been documented in several tributaries of the lower Chesapeake Bay, Virginia. We used annual aerial mapping surveys from 1998 to 2007, integrated with spatial analyses of water quality data, to analyze the patterns and rates of change of a H. verticillata-dominated SAV community and relate them to varying salinity and light conditions. Periods of declining SAV coverage corresponded to periods where salinities exceeded 7 and early growing season (April to May) Secchi depths were <0.4 m. Increases were driven by the expansion of H. verticillata along with several other species into the upper estuary, where some areas experienced an 80% increase in cover. Field investigations revealed H. verticillata dominance to be limited to the upper estuary where total suspended solid concentrations during the early growing season were <15 mg l−1 and salinity remained <3. The effect of poor early growing season water clarity on annual SAV growth highlights the importance of water quality during this critical life stage. Periods of low clarity combined with periodic salinity intrusions may limit the dominance of H. verticillata in these types of estuarine systems. This study shows the importance of the use of these types of biologically relevant episodic events to supplement seasonal habitat requirements and also provides evidence for the potential important role of invasive species in SAV community recovery.

Survey method choice for wildlife management: the case of moose Alces alces in Sweden

AbstractWe need to monitor wildlife populations to determine whether management goals are achieved and to improve future decisions. Therefore, it is important to evaluate the cost and accuracy of monitoring strategies in the context of management. Using a computer simulation of a harvested population, we tested the relative performance of three survey methods: aerial survey, pellet‐group counts and hunters' observations, to inform about the management of Swedish moose Alces alces populations. Where more than one survey method was used in a single year, we used Bayes' theorem to combine information and estimate population size. We used two measures of performance: the fraction of time in which the population had an ‘undesirable’ size and inter‐annual variation in harvest. Furthermore, we traded these performance measures against their cost. An annual aerial survey was the most costly monitoring method (27,000€) and maintained the population within the desired range 72% of the time. The least expensive monitoring strategy (hunters' observations; 1,600€) maintained the population within a desired range of 66% of the time. A combination of two relatively inexpensive survey methods (i.e. pellet‐group counts and hunters' observations; at an expense of 10,000€) maintained the population within the desired range in 76% of the simulated years. Thus, a combination of annual pellet‐group counts and hunters' observations performed better than annual aerial surveys, but was considerably less expensive. Furthermore, the annual combination of pellet‐group counts and hunters' observations also performed best regarding the inter‐annual harvest variation. Management actions only maintained the population within the desired range 81% of the time, even when population size was observed without error, mainly due to variable net growth rates. In wildlife management systems, where a variety of monitoring methods are used, the overall performance generally improves with monitoring expenditure, but very few studies explicitly account for expenditure. However, our study shows that combinations of inexpensive methods can reduce monitoring costs substantially while yielding an equal or an increased performance.

Mountain pine beetle dispersal: spatiotemporal patterns and role in the spread and expansion of the present outbreak

Dispersal has been least understood in mountain pine beetle ecology. We developed a novel regional dynamic conceptual model of mountain pine beetle infestation using the tree mortality estimated from the British Columbia annual aerial overview survey to quantitatively determine short-distance dispersal (SDD) and long-distance dispersal (LDD) at local (forest district) and regional (provincial) scales. The dispersal patterns were characterized based on distances between a sink patch to its nearest source patch. At the regional scale, SDD accounted for 85.3% of mountain pine beetle dispersal to non-infested areas and 96.8% of beetle dispersal to infested areas. Although SDD was a dominant dispersal mode, LDD played a more important role in the early stage of the current mountain pine beetle outbreak. At the local scale, three patterns of dispersal to non-infested areas were identified. First, LDD dominated in the forest districts where only sparse infestations occurred. Second, LDD was a dominant or important factor in the early stages of the infestations in some districts. Third, SDD dominated throughout the infestations in more severely infested forest districts. However, for dispersal to infested areas, SDD was a dominant mode in most of the forest districts. We conclude from the spatiotemporal patterns of dispersal observed at local and regional scales that LDD is a key factor in the initiation and early stage of the infestations in new remote areas, and SDD dominate in the spread and expansion of the outbreak as the infestations intensify and reach epidemic levels. However, it should be conscious that there is uncertainty that LDD might have been over emphasized in the dispersal before local dynamics is fully taken into account.

Impacts of hemlock looper defoliation on growth and survival of balsam fir, black spruce and white birch in Newfoundland, Canada

Hemlock looper ( Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir ( Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce ( Picea mariana (Mill.) B.S.P.) and white birch ( Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71–100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70–80% for black spruce and white birch. Lower defoliation severity (1–2 years of moderate (31–70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10–15% with 1 year of moderate-severe defoliation, 35–40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years.

Relating Climatic Dynamics in Time and Space to Ecological Responses, with Application to Australian Waterbirds

Many animals move in response to climatic variations, with responses of highly mobile species such as waterbirds being especially dynamic. Climatic patterns are commonly quantified through static aggregation of meteorological variables, yet static analyses may only poorly relate to dynamic ecological responses. A technique is developed here to examine relationships between ecological responses and climatic dynamics through quantifying the dynamic structure of large-scale weather systems as they propagate through time and space. Analyses of localized climatic dynamics permit insight into the dependence of ecosystem responses not just upon spatial and temporal scales, but also upon frequencies and prevailing directions, of climatic variation. The technique is applied to the single variable of the aggregate abundance of all species of waterbirds counted in the annual Eastern Australian Aerial Waterbird Survey. The strongest climatic influence on avian abundance is shown to be the coherence of large-scale precipitation systems with spectral frequencies of around 15 days that propagate south-east into the interior of the continent from the tropical north. Directly aggregated rainfall presents a secondary influence. These comprehensively integrative analyses of localized weather are ultimately able to explain over 75% of the inter-annual variance in the aggregate abundance of over 90 species of waterbirds. These results provide a powerful demonstration of the techniques developed here, and reveal the profound extent to which environmental variability structures Australian ecosystems.

Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline

Abstract The Cook Inlet beluga whale, one of five Alaskan stocks, is genetically distinct and geographically isolated from other populations. Historically, Cook Inlet whales were hunted commercially, for sport, and for subsistence uses. The Marine Mammal Protection Act (MMPA) of 1972 ended commercial and sport hunting; in 1999, subsistence hunting voluntarily ended. In 2008, Cook Inlet beluga whales were listed as endangered under the Endangered Species Act after annual aerial surveys indicated the population was not recovering as expected. A combination of natural and anthropogenic factors may be affecting this population’s recovery. This study documented traditional and local ecological knowledge of Alaska Native subsistence hunters and fishers and commercial fishers through participatory research to explore ecological changes in Cook Inlet over time and to identify potential factors impacting this beluga whale population. Study results identified potential environmental and climate change factors including prey competition, health of beluga and their prey, and the presence of killer whales, the majority of which may indicate an ecosystem regime shift in the Cook Inlet region. Human-related factors included fisheries management and related prey reduction, water contamination, and anthropogenic-related noise. These results corroborate identified threats to beluga whales and also identify potential new areas of scientific investigation and management. As such this study demonstrates the value of incorporating traditional and local ecological knowledge into ongoing science and management.

Detecting the equilibrium‐line altitudes of New Zealand glaciers using ASTER satellite images

The glaciers of the Southern Alps of New Zealand play an important role in understanding regional and global patterns of climate change. They constitute the third largest ice mass in the Southern Hemisphere after Antarctica and South America, and present unique glaciological features in the region: high sensitivity, high input‐output systems that represent the temperate, maritime end of glacier process‐behaviour continuum. Since 1977 equilibrium‐line altitudes (ELA) of 48 New Zealand index glaciers have been surveyed using oblique aerial photographs as a low‐cost proxy for monitoring glacier mass balance. Although this method yields good results, it is location‐specific. The use of synoptic high resolution satellite imagery can potentially maximise opportunities to get a wider picture of glacier response to climate variability throughout the New Zealand Southern Alps. Hence, our objective was to investigate how well ELAs detected from 15 m ASTER satellite imagery compare with reference ELAs obtained from aerial photographs taken approximately at the same time, and thus determine whether this imagery could in the future provide a more comprehensive view of glacier wellbeing and trends throughout the Southern Alps. End‐of‐summer ASTER images were selected and orthorectified. Glaciers were extracted, and ice and snow patterns were classified, using supervised classification of principal components. ELAs were digitised and projected over a digital elevation model. The comparison of ELAs gave a mean height departure of 61 ± 55 m, or 14.4 ± 13.4% expressed relative to the glacier elevation range. We conclude that ASTER data could extend ELAs estimated by the current snowline program across the whole Southern Alps. However, small and steep glaciers with complex shapes generate large errors (dominant in the New Zealand context), and thus we suggest that only the largest glaciers can be monitored reliably. ASTER imagery cannot easily replace the annual aerial surveys, mainly because of the difficulty in obtaining the appropriate imagery. The short temporal window, high percentage of cloud cover within the area, and the potential for early unseasonable snowfall are significant limitations to the use of ASTER imagery, without mentioning the recent deterioration of the shortwave infrared ASTER instrument.

Legacy of Insect Defoliators: Increased Wind-Related Mortality Two Decades After a Spruce Budworm Outbreak

Abstract Effects of spruce budworm (Choristoneura fumiferana Clem.) outbreaks on growth and survival of balsam fir (Abies balsamea [L.] Mill.) and spruce (Picea spp.) are well documented, but few studies extend beyond 10 years after defoliation ceased. We used inventory data from 106 permanent sample plots in &amp;gt;50-year-old balsam fir stands in northern New Brunswick, Canada, to determine legacy effects of the 1969–1993 budworm outbreak on stand development up to 29 years after defoliation ceased. Defoliation data were from annual aerial surveys from 1945 to 1993 and plot ground sampling from 1985 to 1993. Plots were stratified into net stand volume development categories (decreasing, stable, and increasing 1985–2005 stemwood volume) and related to outbreak phases (outbreak, direct 1–10 years after defoliation ceased, and legacy &amp;gt;10 years), outbreak severity (1–4 [low], 5–8 [medium], and 9–12 [high] years of defoliation), and stand age (mature and overmature). Stand age was an important factor influencing outbreak severity (e.g., r2 = 0.383, P &amp;lt; 0.01). Trend and rate of volume development over time were related to past outbreak severity and increased rate of postoutbreak wind-related mortality, which peaked at 11 m3/ha/yr 11–15 years after defoliation ceased. Results indicate that aging postoutbreak stands are more vulnerable to wind disturbance events, effecting rapid stand decline.

Effect of management on the spatial spread of mountain pine beetle ( Dendroctonus ponderosae) in Banff National Park

To evaluate control measures, the spread of mountain pine beetles, Dendroctonus ponderosae, in management and monitoring regions in Banff National Park was analyzed for years 1997 to 2004. The Park allowed mountain pine beetles to follow their natural course in a monitoring zone (74,041 ha), whereas in a management zone (45,997 ha) an extensive eradication program was established in 2001 which included baiting mountain pine beetles and cutting and burning all colonized trees. We used data collected from an annual aerial survey and the geo-referenced location of trees that were cut and removed to assess if the area colonized and the spatial extent of mountain pine beetles differed between the two zones. After 4 years, the control measures did not significantly affect the area colonized by mountain pine beetles, and in 2004 mountain pine beetles were still expanding in both zones, although at a slow rate (1.23 ha per year). The spatial extent and the rate at which 500 m × 500 m cells (25 ha) were colonized were much reduced in the management zone. Thus, the management program appeared to have reduced the success of long distance movement as measured by colonizing new 25 ha cells, but short distance dispersal remained successful as indicated by the continued increase in area colonized. The effectiveness of control measures was probably limited by the number of colonized trees that were missed and by survival rates determined by other untested factors.

Comparing population growth rates using weighted bootstrapping: Guiding the conservation management of Petrogale xanthopus xanthopus (yellow-footed rock-wallaby)

In this study we compare estimates of the long-term mean stochastic population growth rates, E[r] for Petrogale xanthopus xanthopus (yellow-footed rock-wallaby), a threatened Australian species. In fluctuating environments such as semi-arid areas, herbivore populations respond directly to changes in the biomass of food resources. Biomass is generally correlated with rainfall, so it is often useful to model annual population growth rates of herbivores directly with rainfall. Models of this nature are referred to as numerical response models. The factors that are thought to threaten this species include competition from introduced herbivores and predation from foxes. Annual aerial survey data collected from 1997 to 2004 over approximately 600km of transect line were analyzed in seven zones within South Australia. Using the Ivlev numerical response model, the annual population growth rates were found to correlate best with the rain that fell in the seven-month period immediately prior to the surveys. Not surprisingly, positive growth rates were found to be associated with higher rainfalls in this period, while negative growth rates were associated with lower rainfalls. We also used weighted bootstrapping to calculate confidence intervals around our estimates of long-term mean stochastic population growth rates, E[r]. The findings suggest that the estimates of E[r] are positive in areas where there is fox and herbivore management. However, we found no evidence that this species will decline in the absence of these treatments.

Wood Stork Nesting in Georgia: 1992-2005

Wood Storks (Mycteria americana) were first recorded nesting in Georgia in 1965 at Blackbeard Island National Wildlife Refuge (Harris 1995). In 1992, biologists initiated annual aerial surveys of known wading bird rookery sites to document Wood Stork distribution and estimate the number of nesting pairs in Georgia. Additionally, personnel from the U.S Fish and Wildlife Service and Savannah River Ecology Laboratory have contributed annual ground-count data for several colonies. Since surveys began, stork nesting has been documented at least once in 43 locations across the Coastal Plain of the state, with an average of 14 active sites per year. The documented nesting effort for storks has increased from four pairs in one wading bird colony in 1965 to a high count of 1,817 pairs in 19 colonies in 2005. A regression of log-transformed nest totals for the 14-year time-series (1992-2005) showed no significant overall trend in nesting pair numbers (P = 0.84) for that period. However, it is possible that an ongoing rebound from a drought-related crash could continue, resulting in an increasing trend. Thirty-three (77%) of stork nesting locations were on private land, with only ten (23%) nesting locations in public ownership. Seven colony sites have supported an average of 68% of the stork nesting effort since 1992; in 2005 these sites supported 77% of the nesting effort. Although not a systematic census of all potential stork nesting habitat, these standardized surveys have produced a useful estimate of Wood Stork population size, distribution, and stability in Georgia. We believe that Georgia’s Wood Stork population has shown an increase in size and distribution, and that numbers can continue to increase or stabilize as long as hydrologic conditions favorable to the species persist.

Measuring the Biological Status of the U.S. Breeding Population of Wood Storks

Abstract In 1984, the U.S. Fish and Wildlife Service listed the U.S. breeding population of Wood Storks (Mycteria americana) in their known range of Florida, Georgia, South Carolina, and Alabama as “endangered” under the Endangered Species Act, due to a population decline of 75 percent from the 1930s to the 1980s. In 1997, an updated Recovery Plan for the Wood Stork established two metrics to for determining the biological status: numbers of nesting pairs and regional productivity measured over time. Five-year averages of nesting pairs from annual aerial surveys show an increasing trend (1981-85, 1991-95, 2001-2005). Since listing in 1984, the average number of active colonies has almost doubled, however colony size has decreased. Current productivity estimates are similar to those recorded in the 1970s and 1980s. Monitoring continues to indicate that nesting numbers and productivity rates are variable within and among years and within and among colonies. Variability is likely related to environmental fac...