MONITORING OF WOOD STORK & WADING BIRD REPRODUCTION IN WCAS 1,2,& 3 OF THE EVERGLADES. Final Report to the

Transcription

1 MONITORING OF WOOD STORK & WADING BIRD REPRODUCTION IN WCAS 1,2,& 3 OF THE EVERGLADES Final Report to the U.S. Army Corps of Engineers San Marco Blvd. Jacksonville, Florida Contract W912EP December 2010 By Peter Frederick Dept. Wildlife Ecology and Conservation P.O. Box University of Florida Gainesville, FL pfred@ufl.edu 1

2 Table of Contents Monitoring of Wood Stork & Wading Bird Reproduction in WCAs 1,2,& 3 of the Everglades... 1 Executive Summary 3 Introduction and Background 6 Methods 10 Wood Storks: Results 12 Weather and water conditions in 2010: Hydrology Water Recession: Temperature: Nesting effort: Dark colored species Reproductive Success: Discussion 27 Progress towards restoration: Literature Cited

3 Executive Summary The numbers of breeding pairs of wading birds in the Everglades and their reproductive success measures have been used for some time to reflect hydrological and biotic conditions in the Everglades, and there is compelling evidence that various aspects of wading bird reproduction and foraging ecology can be mechanistically linked with various aspects of the ecology and hydrology of south Florida wetlands. These relationships are strong enough that wading birds therefore have been chosen as important indicator species for the progress of Everglades restoration, and explicit predictions about specific species and their reproductive reactions have been expressed as a series of trophic hypotheses. This monitoring effort is specifically designed to document the annual reproductive responses of wading birds throughout the ecosystem, including Lake Okeechobee, central and southern Everglades, and Florida Bay. Here, we report on reproduction by wading birds in the 2010 breeding season. The 2010 nesting season (November 2009 July 2010) was exceptionally cold and had numerous rainfall events during the normally dry winter and spring, mostly the result of a strong El Nino event. This caused numerous reversals in the drying trend of water, and near-flat pool conditions in much of the WCAs until late March. The cold was both continuous and extreme, with deviations from normal temperatue being well below one standard deviation below the mean deviation in January, February and March of Cold temperatures probably strongly affected fish and invertebrate availability to birds, with daily low temperatures below thresholds for burrowing and hiding behavior in fishes on 62% of days, and daily mean temperatures below this on 23% of days. In addition, particularly cold snaps and continued cold temperatures may have caused extreme physiological stress on adult birds. By comparison with the recent past, 2010 was an exceptionally low year in terms of numbers of nests and nesting success. We estimated a total of 12,432 wading bird nests were initiated at colonies within LNWR, WCA 2, and WCA 3. This was the lowest number of nests recorded in the WCAs since the current survey protocol was established 3

4 in 2005, was one-third the average of the previous 10 years and less than one-quarter of the banner year in The most significant reduction was observed in WHIB initiations (6X reduction by comparison with 2009). There was no WOST nesting in the WCAS in 2010, and numbers of Roseate Spoonbills were the second smallest since nesting in the WCAS began in the early 2000 s. Reductions in nesting was also true of species that typically do well under conditions that do not concentrate prey. By comparison with 2009, Great Blue Heron nests were decreased in 2010 by 48% and Tricolored Herons by 57%. By comparison with the 5-year average, Tricolored Heron nests were down by 72% and Little Blue Herons were down by 41%. Generally, nest success was much depressed by comparison with most other estimates from the Everglades or reproductive statistics typical of the species. Wood Storks failed at all locations at which they initiated nesting this year. White Ibis nests had less than a 1% probability of fledging at least one young in 2010, while typical figures in good years exceed 50%. For Great Egrets, only 7% of nests fledged at least one young in 2010 and a more typical figure is 70% under good hydrological conditions. Snowy Egrets and Tricolored Herons managed somewhat better, with nest success at 46% and 54%, respectively. These species may have done better because they nested somewhat later and were able to fit their nesting cycle into a period of more consistent drying pattern. In general, brood sizes for nests that did survive were lower than typical for each species. During 2010 there was some progress towards wading bird restoration indicator goals. Storks began nesting in late January, which is earlier than most years in the past, though still a far cry from the November initiations typical of the pre-drainage period. The proportion of nesting in the coastal ecotone was the highest it has been since the 1960s, though it is likely that this was the result of very poor hydrological conditions in the WCAs rather than markedly improved conditions in the coastal ecotone wetlands. The interval between exceptional ibis nesting years is only one since 2009 qualified as an exceptional nesting year (2010 did not). This puts this interval well within the 2-5 year interval typical of the pre-drainage period. The ratio of tactile (ibis + Wood Stork) to 4

5 non-tactile (Great Egret) foragers was quite low in 2010 largely as a result of poor nesting by ibises, and no progress was made on that indicator. In sum, the 2010 nesting year was extremely poor, though not unexpected given the hydrological and temperature conditions that prevailed. While the response by the birds may not be surprising, it is of great interest to know how frequently these conditions may occur in the future, especially under changing global weather patterns. 5

6 Introduction and Background The Water Resources Development Act of 2000 (WRDA) authorized the Comprehensive Everglades Restoration Plan as a framework for modifications and operational changes to the Central and Southern Florida Project needed to restore the south Florida ecosystem. In addition, the USACE as a lead agency in the CERP process has an interest in ensuring that responses of threatened and endangered species are monitored in order to comply with the Endangered Species Act. The Wood Stork (Mycteria americana) is the only stork breeding in the United States, and is a federally endangered species. Wood Storks have special relevance for the restoration of the south Florida ecosystem (encompassing the Kissimmee basin, Lake Okeechobee, the Everglades, Big Cypress, wetlands of southwest Florida, and Florida Bay). Historically, this area was the core reproductive habitat for the species, to the extent that over 75% of the U.S. population was thought to breed in this area (Coulter et al. 1999). The breeding population in the Everglades has declined by over 80% since the 1930s and by at least 50% since the 1960s. In addition, storks have shifted the timing of nesting in the Everglades from November/December initiations, to February/March initiations (Ogden 1994). This shift in timing has meant that storks are usually rear young during the onset of summer rains, when surface water levels rise, prey disperse, and young storks typically starve. In addition, storks have shown marked shifts in the location of nesting, having moved gradually from almost entirely coastal nesting in the Everglades, to inland nesting, as a result of gross dewatering of the coastal regions of the Everglades (Ogden 1994). Storks also began nesting in more northerly locations in north and central Florida, Georgia, and South Carolina during the period These dramatic changes in the characteristics of birds nesting in south Florida has been related to radically altered distribution and timing of surface water in the Everglades (Ogden 1994), as well as an approximately 50% loss of wetlands in Florida since Europeans arrived. Thus the restoration of south Florida wetlands seems to be extremely important to the restoration of breeding Wood Storks to the area. The restoration of storks may also be a signal of successful restoration of key hydrological and biological functions of the south Florida ecosystem (Ogden 1994). By 6

7 virtue of their unique grope-foraging technique, storks seem to require very dense sources of prey animals in order to be cued to nest, and to nest successfully. Their reproduction may thus reflect something about the healthy dynamics of prey animal populations. This is probably not a simple relationship, since dense populations may require one or more kinds of irregular disturbance to achieve pulsed production (Frederick and Ogden 2001). Storks also seem to rely throughout their range on some degree of surface water recession in order to concentrate prey animals successful foraging therefore relies on the right mix of water depth, and water level recession. Thus the regular, successful reproduction of storks may indicate that the combination of several hydrological and biological functions in the Everglades has been correctly restored. Reliance on the storks as an indicator seems wise, since we have a long record of stork nesting (over 80 years), and almost no information on dynamics of aquatic animal populations prior to drainage of the system. The Roseate Spoonbill (Platalea ajaja) is federally listed as Threatened. It is historically been an important nesting bird in the coastal regions of the Everglades, but has also bred in freshwater colonies since at least 1992 (Frederick and Towles 1995) and annually thereafter. Thus this protected species is also of interest because of its potential responses to Everglades restoration activities. The numbers of breeding pairs of wading birds in the Everglades, and their reproductive success measures have been used for some time to reflect hydrological and biotic conditions in the Everglades, and there is compelling evidence that various aspects of wading bird reproduction and foraging ecology can be mechanistically linked with various aspects of the ecology of wetlands, at a variety of scales (Frederick and Ogden 2003, Frederick 2002). While some of these linkages are simple enough to be revealed by short-term studies, a full understanding of the interplay of many variables (eg, hydrology, weather, vegetation, prey and fire cycles) is only possible through the use of long term records. For example, an 80-year record of nesting and hydrology was required to discover that exceptionally large and significant breeding events were almost always preceded by infrequent, severe droughts (Frederick and Ogden 2001). Thus the monitoring of wading birds has been a powerful tool in unraveling the ecology of the birds and the ecosystem, and ongoing monitoring is likely to pay off in 7

8 further understanding and management applications (Frederick and Ogden 2003). First, the long-term nature of the record of the existing nesting record is a powerful context for comparison of any future years. Second, the long term record becomes more powerful with each passing year, particularly for the analysis of the importance of rare combinations of events. Third, a key prediction of the restoration program is that hydrological restoration will result in increased populations of wading birds, earlier nesting for some species, and increased nesting success for some species. While this is a reasonable set of predictions given our understanding of these relationships, there is still a lot of uncertainty in the accuracy (in both space and time) of the prediction. This is because wading bird nesting numbers are probably influenced by alternative nesting opportunities outside the Everglades, and because the influence of contaminants may confound the predicted relationship between hydropattern and nesting. Wading bird nesting is therefore a key criterion of restoration, and aspects of their reproductive ecology (energetics, timing, productivity) have the potential for fine-tuning the way that the hydrology of the Everglades is managed, as well as the relationship between hydrology and nesting. For these reasons, continued monitoring of the Everglades breeding populations is likely to provide crucial information, both for evaluating the progress of restoration, and for refining our understanding of the underlying ecological relationships between the aquatic ecology of the ecosytem and the birds. Although the planning for restoration of the South Florida Ecosystem is well underway, considerable uncertainties remain about the reproductive responses of storks, including how soon storks might respond to a restored ecosystem, where and when they will nest, the relative importance of wetland areas outside the Everglades, and how the population will respond to specific levels of reproductive productivity. Although there is a considerable amount known about the reproductive ecology of storks, there is very little information about the survival or movement patterns of adult and juvenile storks. This has meant that the relative influence of areas outside the Everglades on stork populations is largely unknown, and this lack of understanding could well confound our interpretation of stork responses to restoration. For example, if stork populations respond negatively to restoration, we could (at present) not distinguish between inappropriate restoration as a cause, or appropriate restoration coupled with degenerating habitat quality outside the 8

9 ecosystem. As well, the near-complete lack of information on stork survival has meant that it is impossible to even crudely model stork demographic responses. At the moment, it would be impossible to say whether the current rates of reproduction would result in an increasing, stable, or declining population. This project specifically monitors nesting and nesting success by storks in the Everglades in the hopes of a) detecting ecological changes consistent with restoration, b) contributing to a much larger southeastern-wide picture of stork population change, and c) contributing fecundity inputs to models of stork demographic change. 9

10 Methods We performed two kinds of systematic surveys to document nesting by storks and spoonbills in WCAs 1, 2, and 3 - aerial and ground surveys. Aerial and ground surveys are complementary, and in the Everglades, neither does a particularly good job alone (Frederick et al. 1996). The primary objective of both kinds of surveys is to systematically encounter and document nesting colonies. On or about the 15th of each month between January and June, we performed systematic aerial surveys for colonies, with observers on both sides of a Cessna 182, flight altitude at 800 feet AGL, and eastwest oriented flight transects spaced 1.6 nautical miles apart. These conditions have been demonstrated to result in overlapping coverage on successive transects under a variety of weather and visibility conditions, and have been used continuously since Once colonies were located, we noted positions with a handheld or onboard GPS unit with the aircraft positioned approximately vertically over the north end of the colony. We estimated numbers of visible nesting birds while circling at a variety of altitudes ( feet AGL). Actual positions of colonies were later rectified by visually locating the tree islands on GIS imagery. At small colony sizes (<100 nests), the proportional error in estimating numbers is generally small. However, as colony size grows beyond that, the bias is generally to underestimate numbers (Erwin 1982, Prater 1979), and controlled experiments with simulated counts have demonstrated both large bias (cf 40%) and large inter-observer differences in bias (Frederick et al. 2003). In addition, the latter study also demonstrated that bias can be greatly reduced (by approximately half) through the use of counts of aerial photographs taken at the time of survey. For this reason, in this study digital photographs of the larger colonies were taken from overhead and multiple angles, and counted later via projection. Systematic ground surveys of colonies by airboat were done between early April and late May in selected sections of WCA 3, and were designed to locate and document small colonies or those of dark-colored species that are difficult to detect from aerial surveys. All tree islands were approached closely enough to flush nesting birds, and nests were either counted directly, or estimated from flushed birds. In the past, we have performed systematic, 100% coverage ground surveys of colonies by airboat in WCAs 1, 2 and 3 once between early April and late May. In 2005, 10

11 100% coverage ground surveys throughout the WCAs were discontinued due to a change in MAP guidelines for monitoring (concentrating instead on measuring size and species composition of large colonies of white-colored waders). However, we did perform some systematic ground surveys in WCA 3 that allow for a direct comparison of densities of colonies in certain areas. This was designed to give an index of abundance for small colonies and dark-colored species in a fashion that might be sustainable for the current monitoring effort. It should be clear that this flushing technique works only for smaller colonies, since in large colonies the counting is much more difficult, and many of the birds in the interior would not flush. We conducted ground surveys between 20 March and 15 April The ground survey belt transects in WCA 3A extended from Tamiami Trail to I-75 (Alligator Alley). East/West boundaries for these north/south oriented belts are found in Table 1. Very large colonies were generally few in number and were counted by a combination of aerial survey estimation and photo-counts for white-colored species (as above), and walk-through counts. An example of how these techniques are combined is shown by the Hidden colony (also called in previous years L-28, and 40-mile Table 1. East/West boundaries for Ground Survey transects, WCA 3A. Transect ID East Boundary West Boundary

12 bend ) located in extreme southwestern WCA 3. This colony has substantial numbers of Great Egrets and in some years White Ibises, and usually has large numbers of Snowy Egrets,Tricolored Herons, Anhingas and Little Blue Herons. The colony is largely in dense cypress woods, and visibility from the ground is limited to tens of meters. The Great Egrets, White Ibises and Snowy Egrets are typically counted from aircraft at what was perceived to be their maximum density during incubation periods (February or early March for GREG, late March or April for SNEG). The Tricolored Herons, Anhingas and Little Blue Herons were systematically counted during incubation stage on foot, using 3 6 observers walking abreast, spaced 5 15 m apart along compass lines. Nests of the three small herons (Snowies, Tricoloreds and Little Blues) are indistinguishable unless chicks are present. However, White Ibises and Snowies (which can look similar from the air) were easily distinguished by nest and eggs on the ground. Generally, Snowy Egrets nested in groups that were discernable as the birds flushed. Where chicks were not present, we estimated species proportions of nests based on numbers of birds flushed from particular areas. Wood Storks: We systematically surveyed for Wood Stork colonies from February to June 2004 throughout Water Conservation Areas 1, 2 and 3 using fixed wing aircraft as above We also estimated numbers of young storks per successful nest using either helicopter or fixed wing aircraft when young were between 30 and 45 d of age, based on size (Ogden 1994). After this age the chicks lose their association with the nest, and are difficult to assign to individual nests or even broods. Results Weather and water conditions in 2010: Hydrology. During the wet season of 2009, the Everglades experienced normal rainfall though the onset of the rainy season was several weeks late by some measures. In any case, water 12

13 levels were at or above typical levels by September Although fall drying in the WCAs initially looked promising with a rapid drop in water level between September and October 2009, repeated rainfall events during the fall and winter of 2009/2010 caused water levels thereafter to fluctuate and the net decrease was very modest until late April of 2010 (Figures 1-3). This pattern was exacerbated in WCAs 1 and 3, with nearly flat water during the normal nesting period and repeated reversals during January through June. In the case of the WCAs, there were perhaps six major reversals during this time, depending on what is counted as a reversal Jun-08 9-Sep Dec Mar-09 6-Jul Oct Jan-10 2-May Aug Nov Feb-11 Figure 1. Stage at 3-4 gauge in central WCA 3, (dark line). Stage is shown in relation to mean monthly maximums (X s) and minimums (squares) for the period of record, and one standard deviation in excess of mean monthly maximums (stars) and below minimums (triangles). In Everglades National Park (Figure 3), water levels in Shark Slough initially fell in a fairly ordered fashion throughout the fall of 2009, with only one or two important 13

14 reversals in this trend. However, between January and late April, water levels actually increased substantially, at a time when water levels are historically most likely to fall. In all water management units in the Everglades, water levels in late spring were quite high, generally well above monthly mean maxima, and in some cases at or above one standard deviation of mean monthly maxima Stage at 1-9 in Feet msl /01/08 09/09/08 12/18/08 03/28/09 07/06/09 10/14/09 01/22/10 05/02/10 08/10/10 11/18/10 Figure 2. Stage at 1-9 gauge in central WCA 1, (dark line). Stage is shown in relation to mean monthly maximums (squares) and minimums (X s) for the period of record, and one standard deviation in excess of mean maximums (triangles) and below minimums (stars). 14

15 Stage at P-33 in feet MSL /7/2008 8/15/ /23/2008 3/3/2009 6/11/2009 9/19/ /28/2009 4/7/2010 7/16/2010 Figure 3. Stage at P-33 gauge in central Shark Slough, (dark line). Stage is shown in relation to mean monthly maximums (open squares) and minimums (X s) for the period of record, and one standard deviation in excess of mean maximums (open triangles) and below minimums (stars). The cause of these unusual water levels was clearly the abundant and unseasonable rainfall provided by a strong winter El Nino event, which typically cause much wetter winters in southern Florida than normal. Water Recession: Water level recession rates in winter and spring have been noted as one of the components that can help make prey available to wading birds in the Everglades, and although their power for predicting nesting alone is rather weak, minimum water recession rates of 2 mm/d or greater may be important as a threshold for breeding. Water recession rates are currently used operationally by the SFWMD to enhance breeding whenever possible. 15

16 Table 2. Water level recession rates (mm/d) in the Everglades, with comparisons of the year in question with historical records at each station. Note that negative values indicate rising water, positive values indicate falling water. Percent exceedance refers to the percent of years in the record in which the drying rate is less than that of the current year. % Exceedance % Exceedance % Exceedance Both Early Drying Late Drying Early and Late Drying Year Station Early Dry Late Dry Rate* Rate* Rate* P P A P A A A Recession rates in 2009 and 2010 were exceptionally slow. In WCA 1, both early and late recession rates were negative (= rising water), and were exceeded by (less than) very few of the years on record for the 1-9 gauge. In WCA 3, only 22% of the previous years on record had slower drying rates than The late drying rate was apparently more typical, but represents only the January through March period. Water levels rose between March and April, indicating that the net recession rate during the later part of the nesting season was actually flat or negative. In ENP, the recession rates were quite fast during 16

17 November through January (96% of years on record had slower rates), but none of the years on record had slower recession rates during January through March. Temperature: In addition to being an extremely wet winter, the winter of was also anomalously cold. In January, February, and March, mean deviations from monthly averages were at least one standard deviation in below the mean monthly temperature deviation (Figure 4). Temperature deviations in degrees F above or below monthly means Dec-09 Jan-10 Jan-10 Feb-10 Mar-10 Mar-10 Apr-10 May-10 May-10 Jun Figure 4. Monthly temperature deviations at Tamiami Ranger Station in western Dade County, Florida during the winter of Zero represents average long term monthly deviation from normal temperature. Dashed line connects 2010 monthly deviations from long term mean monthly temperatures. Gray lines indicate one standard deviation above and below the mean monthly deviation. 17

18 Nesting effort: We estimated a total of 12,432 wading bird nests were initiated at colonies within LNWR, WCA 2, and WCA 3 (Tables 3, 4 and 5). This was the lowest number of nests recorded in the WCAs since the current survey protocol was established in The total for 2010 is approximately one-third the average of the previous 10 years and less than one-quarter of the banner year in The most significant reduction was observed in WHIB initiations. This season s estimates are over 6 times smaller than the average of the previous 5-years of about 19,500. While LNWR hosted comparable numbers of WHIB nests this season, the WCAs (specifically Alley North, Hidden, and 6th Bridge) saw only a small fraction of their usual numbers. Like the 2007 and 2008 nesting seasons, this year saw no WOST nesting in our study area, a stark contrast from the 1,433 nests found in Although we did have a small number of Roseate Spoonbills nesting in WCA 3, it was the second smallest number since spoonbills began nesting there in the past decade. The 2010 nesting season can be reliably characterized as an extremely poor nesting year in terms of numbers of nest starts. Trends in total numbers of wading birds in the WCAs (Figure 5 & 6) suggests that total numbers of nest starts have somewhat stabilized since a rapid rise in the early 2000 s. Both ibises and Great Egrets appear to be fluctuating but stable, and stork numbers are too variable to make much of a blanket statement about. Dark colored species: Systematic ground surveys during 2010 of a standard geographic area in WCA 3a suggested numbers of nesting dark-colored species were down as well (Table 7). In 2010, we found only 52% of the Great Blue Heron nests and 43% of the Tricolored Heron nests found in the same area in Compared with the five-year running average, Great Blue nests were down by 30%, Tricolored Herons down by 72%, and Little Blue Herons down by 41%. These decreases may be due to several causes. First, the systematically surveyed area was in central WCA 3, which was deeply flooded in 2010, and birds may have shifted nesting colonies to shallower areas not surveyed in Second, this may have been part of the overall trend in nesting numbers, with nesting curtailed because of poor hydrological and temperature conditions. Finally, there 18

19 is a well defined overall trend towards fewer nests of Tricolored Herons and Little Blue Herons in this area over the last 10 years (Figure 7), and for these species, the trend may simply be carried into Reproductive Success: Generally, nest success was much depressed by comparison with most other estimates from the Everglades or reproductive statistics typical of the species (Table 6). Although Wood Storks began nesting somewhat early at several locations within Everglades National Park, abandonments were common and no nests eventually produced young. White Ibis nests had less than a 1% probability of fledging at least one young in 2010, while typical figures in good years exceed 50%. For Great Egrets, only 7% of nests fledged at least one young in 2010 and a more typical figure is 70% under good hydrological conditions. Snowy Egrets and Tricolored Herons managed somewhat better, with nest success at 46% and 54%, respectively. These species may have done better because they nested somewhat later than ibises, Great Egrets and storks and were able to fit their nesting cycle into a period of more consistent drying pattern in late April and early May. In general, brood sizes for nests that did survive were lower than typical for each species (Table 6). 19

20 Table 3. Total estimated numbers of nests of wading birds by species in all WCAs in GREG WHIB WOST ROSP SNEG GBHE LBHE TRHE GLIB BCNH USW ANHI* Colony Total WCA 1 1,367 3, , ,731 WCA WCA 3 1,677 1, ,701 Total 3,044 5, , ,432 20

21 Table 4. Total estimated numbers of nests of wading birds by species in WCAs 2 and 3 of the Everglades, January through June Latitude Longitude WCA Colony GREG WHIB WOST ROSP SNEG GBHE LBHE TRHE GLIB BCNH USW ANHI* Colony Total Alley N** , th Bridge** Hidden Restin Joule** L-67 (Horus)** Vacation Cypress City** B Mud Canal B Mud East Nammu Juno Jupiter Odin Nanse Air Surveys > 50 Nests 1,486 1, ,983 Air and Ground < 50 Nests*** Totals by Species 1,677 1, ,701 * ANHI Not Reported. See Text ** Estimates of subcanopy nests adjusted based on ground visits *** Includes 360 wading bird nesting pairs discovered from ground surveys 21

22 Table 5. Numbers of wading bird nests by species found in Loxahatchee National Wildlife Refuge, January through June of Latitude Longitude WCA Colony GREG WHIB WOST ROSP SNEG GBHE LBHE TRHE GLIB BCNH USW ANHI* Colony Total Lox 70 (north) 2,700 2, Lox West , Lox , Lox NC Lox NC Venus Welt Air Surveys > 50 Nests 1,252 3, ,327 6,543 Air Surveys < 50 Nests Totals By Species 1,367 3, ,374 6,731 * ANHI Not Reported. See Text 22

23 Table 6. Summary of reproductive statistics for six wading bird species in the Water Conservation Areas of the Everglades, Species Year success 1 success nest Nest s.d. s.d. Fledglings per s.d. Clutch clutch n size size N successful nest 2 fledlgings n Great Egret Great Egret Great Egret 2008 na 6 n.a. Great Egret Great Egret Little Blue Heron 2006 na Little Blue Heron 2009 na Na Little Blue Heron na na Na Snowy Egret 2006 na na Snowy Egret 2009 na Na Snowy Egret na na Na Tricolored Heron na na Na White Ibis White Ibis 2006 na White Ibis White Ibis na na Na Wood Stork Wood Stork na na Na 0.00 na na 23

24 1. proportion of nest starts predicted to raise at least one young to 14 days (White Ibises, small herons), 21 days (Great Egrets) or 28 days (Wood Storks); survival estimated for entire nesting period via pro-rating using Mayfield methods. 2. Numbers of young raised to 14 days (White Ibises and small herons) 21 days (Great Egrets) or 28 days (Wood Storks). 24

25 80000 Numbers of nests in all Everglades Figure 5. Numbers of wading bird nests in all areas, , showing totals of all species (triangles), 5-year running average of totals (dark line), and 5-year running average of White Ibis nests (dashed line) Numbers of Nests Figure 6. Observed numbers of Wood Stork (solid line) and Great Egret (dashed line) nests in the Everglades,

26 Table 7. Numbers of wading bird nests discovered in systematic ground searches within a constant study area within WCA 3, GREG WHIB ANHI GBHE TRHE BCNH SNEG LBHE

27 Numbers of nests in constant survey area TRHE LBHE Figure 6. Numbers of Tricolored Heron and Little Blue Heron nests in the constant survey area in WCA 3A by year. Discussion By comparison with both the recent and the recent past, 2010 was clearly an exceptionally poor year for wading bird reproduction in the Everglades and particularly in the WCAs. The numbers of nests overall were the lowest counted since the mid-1990s, when consistently high water conditions and high mercury contamination both prevailed. The approximately 12,000 nests initiated were less even than the approximately 15,000 found in 2005, also considered a very poor nesting year. All species seemed to be reduced in While this was not surprising for species that rely on concentrated prey for nesting (storks, spoonbills, ibises, Snowy Egrets), we also saw substantial decreases in numbers of Great Egrets, Great Blue Herons, and Tricolored Herons, species that are typically more resilient than tactile foragers especially during reversals and higher water conditions. 27

28 Nest success was quite low for all early nesting species ranging from zero for Wood Storks to near zero for ibises (<1%), and only 7% for Great Egrets. For later nesting small herons, nest success was higher (40-50%) but still low for the species and area. The extremely low nesting success was consistent with the near-stable water levels, interspersed with short periods of rising water during the nesting season. These reversals have been consistently associated with poor feeding and nest abandonment in the past for storks, ibises and to a lesser extent the herons and egrets. In fact, it seems likely that the only reason the small herons did not fail on the same scale as the other species was because they nested up to a month later when water conditions were more consistently falling. Although the effect of water trend on feeding and propensity to nest is well known, the effect of consistently and sometimes extremely cold temperatures is less well known. The availability of prey animals decreases considerably as temperature declines (Frederick and Loftus 1993), and particularly at lower temperatures fishes and invertebrates may simply burrow into the substrate for thermal protection. Prey behaviors that make prey unavailable to birds may begin at temperatures as low as 15 o C. In January, February and March of 2010, daily low temperatures were below this on 57 (63%) of days, and daily mean temperatures were below this for 21 (23%) of the days. Temperature and wind speed rather than hydrological variables were most responsible for explaining nest failure during a series of years for Great Egrets (Frederick and Loftus 1993). In addition to the problem of not being able to obtain enough prey to nest, it is also likely that the extreme and continued cold was responsible for unusual direct physiological stress on adult birds. An anecdotal report from a team looking for cold stunned pythons on a particularly gold morning in January included finding 5 dead or moribund Great Egrets along a canal in the Homestead area. Indeed, severe cold weather can be an important source of mortality for ciconiiform birds (van der Molen et al. 1982, Cezilly et al. 1996). The response to the 2010 nesting season is therefore not particularly surprising given the conditions. Hydrology during the 2010 nesting season was typical in direction for a reasonably strong El Nino winter frequent rain and many reversals. The temperatures were not expected El Ninos generally display higher average winter temperatures than the long term mean, and 2010 was considerably colder. What is of greater interest is how the frequency of this kind of winter weather is likely to be affected by changing global weather patterns. 28

29 Progress towards restoration: 2010 showed only mild improvement in the four key parameters that are monitored for signs of response to restored conditions (Frederick et al. 2008), and mostly because the parameters average past years into the measure. 1. Change in timing of Wood Stork nesting. Storks began nesting earlier this year than they have in the recent past, with initiations as early as late January. While this is not as early as was typical in the historical period (November and December nesting), the trend is certainly an improvement over the trend in the past 20 years (Figure 6). The average for 2010 however now includes none of the years in the early 2000 s that had early nesting and only includes one year in which storks nested earlier than February so the average is considerably lower than for 2009 despite there being no later nesting in 2010 than Nest initiation date index for Storks

30 Figure 6. Index of nest initiation timing for Wood Storks, 1950 s through The index is smaller as storks initiate later in the season, with a 1 corresponding to March initiation, and a 5 corresponding to a November initiation. The index is a 4-year running average of these annual scores. Earliest nesting in 2010 was late January in Everglades National Park. 2. Proportion of Storks + Ibises to Great Egrets A high ratio of tactile foragers (storks + ibises) to sight foragers (Great Egrets) is thought to be a characteristic of the predrainage Everglades, since tactile foragers apparently do better under conditions of very high prey availability. The ratio during the 1930s was thought to be over 30. The ratio in 2010 was 2.17, which is low even by comparison with recent years (Figure 7) Ibis + Stork/Great Egret ratio Figure 7. Ratio of White Ibises plus Wood Stork nests to Great Egret nests. 30

31 3. Interval between exceptional ibis nesting events. During the 1930 s, exceptionally large ibis nestings (70 th percentile of records during the period) occurred once every two to three years. This was thought to have been a response to the relative frequency of exceptional years for feeding when large pulses of prey animals were produced and made available. This measure has improved markedly in recent years (Figure 8), and while both 2007 and 2008 were nonexceptional, 2009 was definitely exceptionally large. The 2010 season however has pushed pushed the interval up to 1 year, and the running average remains below 2 (1.2). This compares favorably with the period (1.67). 30 Interval between exceptional years Figure 8). Interval between exceptional ibis nesting years, defined as the 70 th percentile of the annual nests for the period (for current period, 16,977 nests). Current value for 2010 is 1 year, and running 5-year value is 1.2 years. This is quite similar to the 1 2 year interval typical of the 1930s. 4. Location of nesting. In 2010 the proportion of nesting birds found in the coastal region of the mainland peninsula increased considerably, to over 37% of the total. This is the largest proportion since the mid-1990s, when very high water in the central Everglades forced birds to nest in the coastal areas. The 2010 situation may have been similar, since the Central WCAs had 31

32 very high water all season and birds may have been largely unable to forage there for much of the season. It is unclear whether the coastal zone may have improved in some way itself. The proportion in the coastal zone in 2010 remained well below the 70 90% thought to have nested there in the predrainage system (Figure 9) Proportion of nests in ENP Figure 9. Proportion of all nesting in the Everglades (WCAs 1, 2, 3, and ENP) that occurred in the coastal ecotone of Everglades National Park. 32

33 LITERATURE CITED Cezilly, F., A.Viallefont, V. Boy, and A.R. Johnson Annual variation in survival and breeding probability in Greater Flamingos. Ecology 77: Coulter, M. C., J. A. Rodgers J. C. Ogden and F. C. Depkin Wood Stork. Birds of North America, Eds: A. Poole and F. Gill. No. 409: The Birds of North America, Inc. Philadelphia, PA. Erwin, R. M Observer variability in estimating numbers: an experiment. Journal of Field Ornithology 53: Frederick, P. C Wading Birds in the Marine Environment. In: Biology of Seabirds. Eds. B. A. and J. Burger Schreiber, Boca Raton, Florida: CRC Press. Frederick, P. C., T. Towles, R. J. Sawicki, and G. T. Bancroft Comparison of aerial and ground techniques for discovery and census of wading bird (Ciconiiformes) nesting colonies. Condor 98: Frederick, P.C. and W. F. Loftus Responses of marsh fishes and breeding wading birds to low temperatures; a possible behavioral link between predator and prey. Estuaries 16: Frederick, P. C. and J. C. Ogden Pulsed breeding of long-legged wading birds and the importance of infrequent severe drought conditions in the Florida Everglades. Wetlands 21 (4): Frederick, P. C. and J. C. Ogden Monitoring wetland ecosystems using avian populations: Seventy years of surveys in the Everglades. Pgs in: D. Bush and J. Trexler, Eds. "Interdisciplinary approaches for evaluating ecoregional initiatives". Island Press, Washington D.C.447 pgs. Frederick, P. C. B. A. Hylton J. A. Heath and M. Ruane Accuracy and variation in estimates of large numbers of birds by individual observers using an aerial survey simulator. Journal of Field Ornithology 74: Frederick, P.C., D. E. Gawlik, J.C. Ogden, M. Cook and M. Lusk The White Ibis and Wood Stork as indicators for restoration of the Everglades ecosystem. Ecol. Indicators. 33

34 Ogden, J. C A comparison of wading bird nesting dynamics, and as an indication of changes in ecosystem conditions in the southern Everglades. in: Everglades: the ecosystem and its restoration. Eds. S. and J. C. Ogden Davis, pp. Del Ray Beach, Florida: St. Lucie Press. Prater, A. J Trends in accuracy of counting birds. Bird Study 26: Van der Molen EJ, Blok AA, De Graaf GJ (1982) Winter starvation and mercury intoxication in grey herons (Ardea cinerea) in the Netherlands. Ardea. 70: