Novel Snowy Egret Foraging Behavior

Volume: 119Start Page: 116End Page: 11

Social Cues and Environmental Conditions Influence Foraging Flight Distances of Breeding Wood Storks (Mycteria americana)

The influence of both environmental conditions and social cues on the distance flown to foraging sites was examined for breeding Wood Storks (Mycteria americana) in the Florida Everglades, USA. Adult Wood Storks (n = 73) were followed in a small plane from their nesting colony to their foraging locations during the time when adult Wood Storks were incubating and feeding chicks. On average, foraging sites were close to the nesting colony (mean = 9.6 km ± 1.1), and in shallow water (mean = 9.9 cm ± 0.7) that was receding at a moderate rate (-0.36 cm/day ± 0.13). Wood Storks landed at foraging sites already occupied by other white wading birds 99% of the time, with a mean flock size of 64 ± 14 birds. Model selection identified flock size and water recession rate as the most important variables that influenced Wood Stork foraging flight distances. Distances flown to foraging sites increased with increasing flock sizes and decreased with increasing recession rates (increasing by 39% and decreasing by 18% across the observed range of data, respectively) while accounting for colony location and water depths. These findings are particularly important because they demonstrate that both social and environmental factors play critical roles in the foraging site selection process Wood Storks use during the breeding season. Further, these results in part can be linked to management activities because at least in the case of water recession rates, managers can actively influence recession rates across much of the Everglades landscap

Stability of Avian Fecal Corticosterone Metabolite Levels in Frozen Avian Feces

Fecal corticosterone metabolites are commonly used in avian ecology as a measure of response to stress. Recent research on mammals suggested that the manner in which samples are stored could be critical to alleviating any storage handling bias. Cross-reacting metabolites can increase glucocorticoid metabolites even after samples are frozen and, thus, result in an overestimation of hormone levels as the time increases between when samples were collected and when levels are measured. We examined effects of sample storage time on fecal corticosterone metabolites for 2 avian species across 165 days. We observed no change in fecal corticosterone metabolites across the sampling periods in either fulvous whistling-ducks (Dendrocygna bicolor) or white ibis (Eudocimus albas). Results suggest that avian fecal corticosterone metabolite levels do not change when samples are frozen for long periods of time and that there were no differences in the response between the 2 species we compared. This study demonstrated that avian fecal corticosterone samples are accurate even after freezing and, thus, studies that seek to address conservation questions may rely on these data. Studies of additional bird species are needed to generalize our findings to other avian taxa

Potential for successful population establishment of the nonindigenous sacred ibis in the Florida Everglades

The nonindigenous sacred ibis (Threskiornis aethiopicus) was first discovered breeding in the Florida Everglades in 2005 in the Arthur R. Marshall Loxahatchee National Wildlife Refuge. Prior to this, sacred ibises were seen periodically throughout South Florida since the mid 1990s, with occasional confirmed breeding occurrences in Miami-Dade and Palm Beach counties. We used a logistic regression model developed by Allen (Biol Invasions 8:491–500, 2006) to predict the probability of successful establishment of sacred ibis in the Florida Everglades ecosystem. Empirical data collected from several sacred ibis nests and chicks were used to validate those findings. The probability of successful establishment was estimated to be 73%. The physiological condition of nestlings suggested that this species was able to fledge chicks in good condition, thus adding to the potential to increase their breeding population. Exponential population growth rates and expanding distribution of the nonindigenous sacred ibis in France demonstrate this species’ potential for becoming invasive in Florida. We suggest that the most prudent and effective management strategy is eradication of the few pioneering individuals that are nesting in the Everglades as well as the urban source population

Avian Radio-transmitter Harness Wear and Failure

Although investigators have compared radio-transmitter attachment devices and their likelihood of failure before the end of a study, few have directly evaluated the harness materials and fastening methods that are to be shed by a bird after the research period is over. We compared the likelihood of effective detachment after transmitter life of four harness materials (7-mm- and 9-mm-wide polyester rib- bon tape and polyester-coated rubber elastic) and three fastening methods (polyester thread, cotton thread, and Gorilla Super Glue™) using dummy transmitters exposed to the elements for >1.5 years. Both polyester ribbon and polyester-coated rubber elastic materials resulted in similar physical wear and remained intact for longer than a typical field seasonal, but fastening harnesses using Gorilla Super Glue™ resulted in the earliest and most consistent harness failure. Polyester ribbon material and glue fastening resulted in the earliest failure; mean failure time for 7-mm- and 9-mm-wide polyester ribbon tape with glue fastening was 408 days ±30 SE, and 249 days ± 29 SE, respectively. Failure times for both 7-mm- and 9-mm-wide polyester- coated rubber elastic and Gorilla Super Glue™ fastening treatments were in excess of one year (438 days ± 14 SE and 438 days ± 13 SE, respectively). All harnesses with sewn thread fastening treatments lasted a minimum mean of 456 days, and i the case of both 7-mm-wide polyester ribbon and polyester-coated rubber elastic neither treatment ever failed over the period of study. Results suggest that using Gorilla Super Glue™ as a fastener maximized the likelihood of eventual harness failure, whereas transmitters fastened via sewing showed minimal signs of wear an were unlikely to be shed by a bird during a period of time less than two years. Additional experimental studies are warranted to examine alternative harness material types, fastening methods, and harness styles to maximize the potential of successful radio transmitter shedding

The Role of Stress Proteins in the Study of Allostatic Overload in Birds: Use and Applicability to Current Studies in Avian Ecology

Stress proteins offer a measure of stress in birds at the cellular level that are an alternative to the glucocorticoids. Stress proteins are not biased by handling stress, the increase in stress proteins lasts longer than with other measures (e.g., corticosterone), and, therefore, they may be a more appropriate measure of long-term or chronic stress. However, caution should be practiced when using stress proteins because the level of stress needed to elicit a response may be higher than with corticosterone. Stress proteins have only recently been used to measure the response to competition, food limitation, growth, and parasitism in birds. In other taxa, the stress proteins have been used to measure genetic stress, temperature, toxins, UV radiation, and physical activity. Stress proteins increase the options available to avian ecologists for understanding how avian species respond to changes in the environment

Multiple Nest-Tending Behavior in an Adult Female White Ibis

A non-breeding adult female White Ibis (Eudocimus albus) was observed tending multiple nests during the 2006 wading bird breeding season in the Florida Everglades. This is the first known case of adult multiple nest-attending breeding behavior documented for the Ciconiiformes order

Sex Determination for the Great Egret and White Ibis

Most species of wading birds are monomorphic and present few or no external characteristics to al-low for sex determination in the field. We used standard morphometric measurements and discriminant function analysis to determine the sex of Great Egrets ( Ardea alba ) and White Ibises ( Eudocimus albus ). The models were validated based on sex determination from DNA. Two functions were created for Great Egrets; mass reliably discriminated 88% of our samples, while wing chord separated 81% of our samples. We included mass in the discriminant function analysis for Great Egrets because mass did not vary between years or within our pre-breeding sampling period. Mass was not included in our analysis of White Ibis because it differed by year and within our pre-breeding sampling period. White Ibis samples were separated by a discriminant function using the length of curved bill and tarsus. This function correctly classified 78% of our samples. We provide simplified linear equations to calculate the sex of Great Egrets and White Ibises as well as cut off points where the probability of correctly sexing individuals drops below 75%. Our model can be used to reduce the costs of sex determination by allowing researchers to use expensive DNA analysis techniques only for those individuals that cannot be reliably classified using the simple statistical model