Mark P. Herzog

Density-dependent effects on growth, body size, and clutch size in black brant

-We documented gosling size in late summer, adult body size, and clutch size of known-age Black Brant (Branta bernicla nigricans) females nesting on the Tutakoke River colony between 1986 and 1995. During this period, the colony increased from 1,100 to >5,000 nesting pairs. Gosling mass at 30 days of age declined from 764 + SE of 13 g and 723 ? 15 g for males and females, respectively, in the 1986 cohort, to 665 + 18 g and 579 ? 18 g in the 1994 cohort. Gosling size was directly negatively correlated with number of Black Brant broods. We detected no trend in adult body size for individuals from these cohorts; in fact, adults from the 1992 and 1994 cohorts had the largest overall masses. Clutch size increased with age from 3.4 eggs for 2-year-old females to 4.4 eggs for 5-year-old females. Clutch size declined during the study by 0.20 (3-year-old females) to 0.45 (2-year-old females) eggs. Clutch size did not decline between the 1986 and 1990 cohorts for females that were >5 years old. Our results for clutch size and gosling size are similar to those recorded for Lesser Snow Geese (Chen caerulescens caerulescens). Our failure to detect a trend in adult body size, however, differs from the response of other geese to increasing population density. We interpret this difference in effects of density on adult size between Black Brant and other geese as an indication of stronger selection against the smallest individuals in Black Brant relative to other species of geese. Received 19 May 1997, accepted 17 November 1997. ARCTIC-NESTING GEESE are strictly herbivorous during the breeding season (Owen 1980, Sedinger 1992) and are selective of the most nutritious foods and habitats containing these foods (Lieff 1973, Harwood 1975, Sedinger and Raveling 1984, Gadallah and Jefferies 1995a, b). Despite these strong preferences, substantial variation exists in growth rates of goslings, which likely is associated with temporal and spatial variation in habitat quality (Cooch et al. 1991a, Larsson and Forslund 1991, Sedinger and Flint 1991, Aubin et al. 1993). Because gosling growth is associated with future survival and fecundity (Larsson and Forslund 1991, 1992, Francis et al. 1992, Rockwell et al. 1993, Sedinger et al. 1995b), habitat quality likely is directly linked to processes determining population dynamics. Sedinger and Raveling (1986) argued that seasonal declines in nutrient I E-mail: ffjss@aurora.alaska.edu 2 Present Address: Institute for Wetland and Waterfowl Research, Ducks Unlimited Inc., One Waterfowl Way, Memphis, Tennessee 38120, USA. 3Present Address: Alaska Science Center, Division of Biological Resources, U.S. Geological Survey, 1011 East Tudor Road, Anchorage, Alaska 99503, USA. concentration in the diet of Cackling Canada Geese (B. canadensis minima) resulted from reduced availability of the highest-quality foods because of grazing by geese. Lesser Snow Geese (Chen caerulescens caerulescens) substantially reduce the abundance of preferred food plants (Cargill and Jefferies 1984, Hik and Jefferies 1990), as do some Black Brant (B. bernicla nigricans; hereafter brant; Person et al. 1998). The relationship between nutrient intake by goslings and demographic parameters creates the potential for per capita availability of foods of sufficient quality during brood rearing to influence population dynamics. Long-term declines in body size and fecundity have been associated with increased size of a colony of Lesser Snow Geese, and Cooch et al. (1991a, b) and Francis et al. (1992) demonstrated a decline in juvenile survival for this colony over the same period. The number of brant nesting on the YukonKuskokwim (Y-K) Delta declined by more than 60% in the 1970s and early 1980s (Sedinger et al. 1993), likely as a result of human harvest (Sedinger 1996) and predation by arctic foxes (Alopex lagopus; Anthony et al. 1991, Sedinger et al. 1993). Reduced predation and harvest were as-

Bird Mercury Concentrations Change Rapidly as Chicks Age: Toxicological Risk is Highest at Hatching and Fledging

Toxicological risk of methylmercury exposure to juvenile birds is complex due to the highly transient nature of mercury concentrations as chicks age. We examined total mercury and methylmercury concentrations in blood, liver, kidney, muscle, and feathers of 111 Forsters tern (Sterna forsteri), 69 black-necked stilt (Himantopus mexicanus), and 43 American avocet (Recurvirostra americana) chicks as they aged from hatching through postfledging at wetlands that had either low or high mercury contamination in San Francisco Bay, California. For each waterbird species, internal tissue, and wetland, total mercury and methylmercury concentrations changed rapidly as chicks aged and exhibited a quadratic, U-shaped pattern from hatching through postfledging. Mercury concentrations were highest immediately after hatching, due to maternally deposited mercury in eggs, then rapidly declined as chicks aged and diluted their mercury body burden through growth in size and mercury depuration into growing feathers. Mercury concentrations then increased during fledging when mass gain and feather growth slowed, while chicks continued to acquire dietary mercury. In contrast to mercury in internal tissues, mercury concentrations in chick feathers were highly variable and declined linearly with age. For 58 recaptured Forsters tern chicks, the proportional change in blood mercury concentration was negatively related to the proportional change in body mass, but not to the amount of feathers or wing length. Thus, mercury concentrations declined more in chicks that gained more mass between sampling events. The U-shaped pattern of mercury concentrations from hatching to fledging indicates that juvenile birds may be at highest risk to methylmercury toxicity shortly after hatching when maternally deposited mercury concentrations are still high and again after fledging when opportunities for mass dilution and mercury excretion into feathers are limited.

Large-Scale Variation in Growth of Black Brant Goslings Related to Food Availability

Abstract We examined variation in growth of Black Brant (Branta bernicla nigricans) goslings among two colonies on the Yukon-Kuskokwim Delta in southwestern Alaska and the Colville River Delta on Alaskas Arctic coast. We simultaneously measured abundance and quality of a key food plant, Carex subspathacea, and grazing pressure on that plant at the three colonies. Our goal was to measure variation in gosling growth in relation to variation in grazing pressure and food abundance because growth of goslings is directly linked to first-year survival, and consequently is the principal mechanism for density-dependent population regulation. Goslings grew substantially faster on the arctic coast and were nearly 30% larger than those on the Yukon-Kuskokwim Delta at four to five weeks old. Faster growth on the arctic coast was associated with 2× greater standing crop of C. subspathacea during brood rearing than on the Yukon-Kuskokwim Delta. Dispersal rates are high enough (Lindberg et al. 1998) to rule out local adaptation and genetic variation as explanations for observed variation in growth. Our results are consistent with lower survival of goslings from the Yukon-Kuskokwim Delta during their first fall migration and stronger density-dependent regulation on the Yukon-Kuskokwim Delta than on the Arctic coast.

A sampling design framework for monitoring secretive marshbirds

Abstract. A framework for a sampling plan for monitoring marshbird populations in the contiguous 48 states is proposed here. The sampling universe is the breeding habitat (i.e. wetlands) potentially used by marshbirds. Selection protocols would be implemented within each of large geographical strata, such as Bird Conservation Regions. Site selection will be done using a two-stage cluster sample. Primary sampling units (PSUs) would be land areas, such as legal townships, and would be selected by a procedure such as systematic sampling. Secondary sampling units (SSUs) will be wetlands or portions of wetlands in the PSUs. SSUs will be selected by a randomized spatially balanced procedure. For analysis, the use of a variety of methods as a means of increasing confidence in conclusions that may be reached is encouraged. Additional effort will be required to work out details and implement the plan.

Methylmercury is the Predominant Form of Mercury in Bird Eggs: A Synthesis

Bird eggs are commonly used in mercury monitoring programs to assess methylmercury contamination and toxicity to birds. However, only 6% of >200 studies investigating mercury in bird eggs have actually measured methylmercury concentrations in eggs. Instead, studies typically measure total mercury in eggs (both organic and inorganic forms of mercury), with the explicit assumption that total mercury concentrations in eggs are a reliable proxy for methylmercury concentrations in eggs. This assumption is rarely tested, but has important implications for assessing risk of mercury to birds. We conducted a detailed assessment of this assumption by (1) collecting original data to examine the relationship between total and methylmercury in eggs of two species, and (2) reviewing the published literature on mercury concentrations in bird eggs to examine whether the percentage of total mercury in the methylmercury form differed among species. Within American avocets (Recurvirostra americana) and Forsters terns (Sterna forsteri), methylmercury concentrations were highly correlated (R(2) = 0.99) with total mercury concentrations in individual eggs (range: 0.03-7.33 μg/g fww), and the regression slope (log scale) was not different from one (m = 0.992). The mean percentage of total mercury in the methylmercury form in eggs was 97% for American avocets (n = 30 eggs), 96% for Forsters terns (n = 30 eggs), and 96% among all 22 species of birds (n = 30 estimates of species means). The percentage of total mercury in the methylmercury form ranged from 63% to 116% among individual eggs and 82% to 111% among species means, but this variation was not related to total mercury concentrations in eggs, foraging guild, nor to a species life history strategy as characterized along the precocial to altricial spectrum. Our results support the use of total mercury concentrations to estimate methylmercury concentrations in bird eggs.

Avian mercury exposure and toxicological risk across western North America: a synthesis

Methylmercury contamination of the environment is an important issue globally, and birds are useful bioindicators for mercury monitoring programs. The available data on mercury contamination of birds in western North America were synthesized. Original data from multiple databases were obtained and a literature review was conducted to obtain additional mercury concentrations. In total, 29219 original bird mercury concentrations from 225 species were compiled, and an additional 1712 mean mercury concentrations, representing 19998 individuals and 176 species, from 200 publications were obtained. To make mercury data comparable across bird tissues, published equations of tissue mercury correlations were used to convert all mercury concentrations into blood-equivalent mercury concentrations. Blood-equivalent mercury concentrations differed among species, foraging guilds, habitat types, locations, and ecoregions. Piscivores and carnivores exhibited the greatest mercury concentrations, whereas herbivores and granivores exhibited the lowest mercury concentrations. Bird mercury concentrations were greatest in ocean and salt marsh habitats and lowest in terrestrial habitats. Bird mercury concentrations were above toxicity benchmarks in many areas throughout western North America, and multiple hotspots were identified. Additionally, published toxicity benchmarks established in multiple tissues were summarized and translated into a common blood-equivalent mercury concentration. Overall, 66% of birds sampled in western North American exceeded a blood-equivalent mercury concentration of 0.2 μg/g wet weight (ww; above background levels), which is the lowest-observed effect level, 28% exceeded 1.0 μg/g ww (moderate risk), 8% exceeded 3.0 μg/g ww (high risk), and 4% exceeded 4.0 μg/g ww (severe risk). Mercury monitoring programs should sample bird tissues, such as adult blood and eggs, that are most-easily translated into tissues with well-developed toxicity benchmarks and that are directly relevant to bird reproduction. Results indicate that mercury contamination of birds is prevalent in many areas throughout western North America, and large-scale ecological attributes are important factors influencing bird mercury concentrations.

Early environment and recruitment of black brant ( Branta bernicla nigricans ) into the breeding population

Abstract In geese, growth regulates survival in the first year. We examined whether early growth, which is primarily governed by environmental conditions, also affects the probability that individuals that survive their first year enter the breeding population. We used logistic regression on a sample of Black Brant (Branta bernicla nigricans) that were weighed at a known age in their first summer and observed during winter (indicating that they had survived the principal mortality period in their first year) to study whether early growth influenced the probability that those individuals would be recruited into the breeding population. We also examined the effects of cohort (1986–1996), sex, age when measured, and area where individuals were reared. The model with the lowest Akaikes Information Criterion score contained body mass, age (days) at measurement, cohort, sex, and brood-rearing area. Models that included variable mass had 85% of the cumulative model weight of the models we considered, indicating that gosling mass had a substantial effect on probability of them entering the breeding population. Females were more likely to be detected breeding than males, which is consistent with the differential fidelity of the sexes. Of individuals that survived the first year, larger goslings were more likely to become breeders. More recent cohorts were less likely to have been detected as breeders. Our findings indicate that environment during the growth period affects the ability of individuals to enter the breeding population, even after accounting for the effects of growth on survival.

Does mercury contamination reduce body condition of endangered California clapper rails

We examined mercury exposure in 133 endangered California clapper rails (Rallus longirostris obsoletus) within tidal marsh habitats of San Francisco Bay, California from 2006 to 2010. Mean total mercury concentrations were 0.56 μg/g ww in blood (range: 0.15-1.43), 9.87 μg/g fw in head feathers (3.37-22.0), 9.04 μg/g fw in breast feathers (3.68-20.2), and 0.57 μg/g fww in abandoned eggs (0.15-2.70). We recaptured 21 clapper rails and most had low within-individual variation in mercury. Differences in mercury concentrations were largely attributed to tidal marsh site, with some evidence for year and quadratic date effects. Mercury concentrations in feathers were correlated with blood, and slopes differed between sexes (R(2) = 0.58-0.76). Body condition was negatively related to mercury concentrations. Model averaged estimates indicated a potential decrease in body mass of 20-22 g (5-7%) over the observed range of mercury concentrations. Our results indicate the potential for detrimental effects of mercury contamination on endangered California clapper rails in tidal marsh habitats.

Mercury exposure may suppress baseline corticosterone levels in juvenile birds.

Mercury exposure has been associated with a wide variety of negative reproductive responses in birds, however few studies have examined the potential for chick impairment via the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis regulates corticosterone levels during periods of stress. We examined the relationship between baseline fecal corticosterone metabolite concentrations and mercury concentrations in down feathers of recently hatched (<3 days) and blood of older (15-37 days) Forsters tern (Sterna forsteri) chicks in San Francisco Bay, California. Baseline fecal corticosterone metabolite concentrations were negatively correlated with mercury concentrations in blood of older chicks (decreasing by 81% across the range of observed mercury concentrations) while accounting for positive correlations between corticosterone concentrations and number of fledgling chicks within the colony and chick age. In recently hatched chicks, baseline fecal corticosterone metabolite concentrations were weakly negatively correlated with mercury concentrations in down feathers (decreasing by 45% across the range of observed mercury concentrations) while accounting for stronger positive correlations between corticosterone concentrations and colony nest abundance and date. These results indicate that chronic mercury exposure may suppress baseline corticosterone concentrations in tern chicks and suggests that a juvenile birds ability to respond to stress may be reduced via the downregulation of the HPA axis.

Impacts of Salinity on Growth and Behavior of American Avocet Chicks

Abstract The impact of anthropogenically-caused salinization on wildlife is a conservation issue of global concern. Increasing salinization of inland wetlands is especially problematic for breeding and migrating birds. In the arid American west, inland wetlands are centers of avian biodiversity, providing habitat for millions of birds. We experimentally examined the effects of different salinity levels on the growth, health and behavior of American Avocets (Recurvirostra americana) chicks. Birds raised in highly saline conditions exhibited significant changes in behavior, including increased activity and decreased feeding and preening. High salinity resulted in significant weight loss of 4.4 g by day 3. Blood measures of chick health indicated that hypersaline-raised chicks suffered from dehydration (e.g., osmolality of chicks reared in brackish water was 305, compared with 381 among chicks reared in hypersaline water). Results of this study, and similar studies on ducks, geese and egrets, indicate that waterbirds in general suffer adverse effects when living in highly saline environments, without access to freshwater. We recommend that water managers ensure the maintenance of freshwater inflows to wetlands throughout the breeding season.