Aaron R. Pierce

IS REPRODUCTION BY TREE SWALLOWS COST FREE

Abstract We manipulated brood sizes of Tree Swallows (Tachycineta bicolor) in 1996 and 1997 to test for the existence of intra- and intergenerational costs of reproduction. Modal clutch size was six eggs, but experimental brood sizes ranged from two to nine young. Nestling starvation was higher in 1996 (and dependent on brood size) than in 1997, but in both years enlargement of brood size resulted in increased productivity. Nestling mass near fledging was negatively correlated with brood size, but tarsus length and wing chord were not. Food deliveries by parents increased steadily between broods of two to six young but then remained constant between broods of six to nine young. The loss of female mass between incubation and the end of the nestling period was positively related to the pairs total feeding effort, and female mass near fledging declined with increasing brood size. The latter decline disappeared, however, when broods of nine were omitted. Adult return rate (1996 to 1997) was highest among birds that raised enlarged broods. Our results, and a review of other studies of Tree Swallows, suggest that broods of seven or eight young can be raised without costs to the parents or young, and it appears that costs associated with feeding young have not influenced annual fecundity of Tree Swallows. Rather, egg production is most likely limited by energy availability to laying females. A major cost of reproduction for Tree Swallows probably arises from nest-site competition in that early arrival in spring to obtain nest sites exposes adults to high risks of death from starvation.

Forest Succession in an Oak-Hickory Dominated Stand During a 40-Year Period at the Ross Biological Reserve, Indiana

Abstract Deciduous forests in the eastern United States have been dynamic over both geological and historical time scales, particularly since humans have modified the landscape. Historically, the central hardwood forest has been subject to considerable human disturbance, especially fire, and these anthropogenic disturbances have contributed to the dominance of shade-intolerant oak (Quercus) and hickory (Carya) species within the central hardwood region. Current research indicates that many of these forests are changing to dominance by shade-tolerant species, mainly sugar maple (Acer saccharum Marsh.). This change has been attributed to a lack of disturbance. The objective of this study was to document long-term changes in structure and composition of a mature oak-hickory stand at the Ross Biological Reserve in Indiana. There has been little disturbance at the Ross Biological Reserve in the past 55 years, and a similar trend of increased shade-tolerant species was expected. Results of decadal tree censuses suggest that a successional change toward the dominance of sugar maple has been occurring during the 40-year study period, and an abundance of sugar maple saplings suggests that the increasing importance of sugar maple will continue with a lack of disturbance. The increased abundance of sugar maple may be having a negative effect on regeneration of oak-hickory species as well as on understory species such as flowering dogwood (Cornus florida L.). Such changes in the plant community also suggest changes in resources for animals. Management of the Ross Biological Reserve, and similar areas, requires an appreciation of forest dynamics on a variety of time scales.

THE EFFECTS OF FLOODING AND SEDIMENTATION ON SEED GERMINATION OF TWO BOTTOMLAND HARDWOOD TREE SPECIES

Flooding and sedimentation are two of the dominant disturbances that influence tree species composition and succession in floodplain forests. The importance of these disturbances may be most notable during the germination and establishment phases of plant succession. Channelization of most alluvial systems in the southeastern United States has caused dramatic and systematic alterations to both hydrologic and sedimentation processes of floodplain systems. We determined the influence of these altered abiotic processes on the germination and growth of two common floodplain tree species: swamp chestnut oak (Quercus michauxii Nutt.) and overcup oak (Q. lyrata Walt.). Flood durations of 0 days, 15 days, and 30 days prior to germination was a factor in germination, but the effect varied by species. For instance, overcup oak, which has a higher tolerance to flooding than swamp chestnut oak, had higher germination rates in the flooded treatments (15-day -x = 78% and 30-day -x = 85%) compared to the non-flooded treatment (-x = 54%). In contrast, germination rates of swamp chestnut oak were negatively affected by the 30-day flood treatment. Sediment deposition rates of 2 cm of top soil, 2 cm of sand, and 8 cm of sand also affected germination, but were secondary to flood duration. The main effect of the sediment treatment in this experiment was a reduction in above-ground height of seedlings. Our study provides evidence for the importance of both flooding and sedimentation in determining tree species composition in floodplain systems, and that tolerance levels to such Stressors vary by species.

Population structure and habitat use by overwintering neotropical migrants on a remote oceanic island

Abstract We studied habitat use by migrant birds on the island of San Salvador using mist nets during January of 4 years (1997–2000). Information on capture rates, body mass, age-sex class distribution, frequency of recapture, and return rate were used to determine preferences for early successional habitat, mangrove, scrub or secondary forest. We captured 23 species (19 parulid warblers), but focused our attention on the 14 most abundant species (750 individually marked birds). A group of four abundant species exhibited equal sex ratios, but a female bias existed among common and uncommon species [e.g. black-throated blue warblers ( Dendroica caerulescens ) and American redstarts ( Setophaga ruticilla )]. Twelve of 14 species used habitats unevenly. Habitat use also varied with age–sex class in prairie warblers ( D. discolor ) and redstarts: in both, males used secondary forests and females used early successional habitat. Palm warblers also showed high variability in habitat use among years. Body mass did not vary with habitat in most species, but more stressful conditions late in the dry season might reveal differences. Return rates to the island were significantly lower than estimates obtained for the same species elsewhere in the Caribbean and Central America, and were of little use in identifying preferred habitats. However, most recaptures (within and between seasons) were made in the habitat where capture rates were highest. Interspecific differences in capture rate were thus indicative of habitat preferences. Based on this criterion, six of the 14 species preferred early successional habitat. Every habitat, however, was used heavily by at least three species. These latter findings, and the sex- and age-specific patterns of habitat segregation, emphasize the importance of maintaining habitat diversity for the conservation of neotropical migrants.

THE INFLUENCE OF VALLEY PLUGS IN CHANNELIZED STREAMS ON FLOODPLAIN SEDIMENTATION DYNAMICS OVER THE LAST CENTURY

Channelization of alluvial systems alters the functions and processes of floodplain ecosystems. In the loess belt region of western Tennessee and northern Mississippi, channelization, the geology of the region, and past land-use practices have resulted in geomorphic readjustments of streams and the formation of valley plugs. Valley plugs completely block stream channels with sediment and debris, and can result in greater deposition rates on floodplain surfaces. We used dendrogeomorphic techniques to quantify floodplain sediment deposition rates from the last 100+ years. The data were used to determine the spatial and temporal patterns of sedimentation in floodplains affected by channelization and the subsequent formation of valley plugs and in floodplains along unchannelized streams. We measured sediment accumulation by coring trees for age determination and measuring depth to the root collar of 63 trees at unchannelized sites and 214 trees at channelized valley plug sites. Mean floodplain deposition rates were greater at valley plug sites (-x = 1.71 ± 0.08 cm/yr) compared to rates at unchannelized sites (-x = 0.31 ± 0.02 cm/yr). The formation of valley plugs in channelized streams also affected the spatial and temporal patterns of sedimentation. Increases in deposition rates at the valley plug sites occurred approximately 30 years ago and corresponds to the timing of regional activities including: channelization projects, increases in agricultural activity, and the termination of stream dredging projects.

Short-Term Demographic Responses of a Coastal Waterbird Community After Two Major Hurricanes

Abstract. Response of breeding waterbird communities to the effects of hurricanes remains poorly understood. The impact of two 2008 hurricanes on the breeding waterbird community was investigated at the Isles Dernieres Barrier Island Refuge in southern Louisiana using pre- and post-hurricane survey data. After the 2008 hurricanes, the breeding community was reduced from 44,042 breeding pairs in 2008 to 27,977 pairs in 2009 and to 23,544 pairs in 2010. Populations of the five most abundant species, Brown Pelican (Pelecanus occidentalis), Laughing Gull (Leucophaeus atricilla), Royal Tern (Thallasseus maximus), Sandwich Tern (Thallasseus sandvincensis), and Black Skimmer (Rynchops niger), decreased from 2008 to 2010. In contrast, populations of Roseate Spoonbill (Platalea ajaja), Sooty Tern (Onychoprion fuscatus), and Gull-billed Tern (Gelochelidon nilotica) increased from 2008 to 2009 but declined in 2010. The dramatic decline of total breeding pairs in the year following hurricanes demonstrates the vulnerability of this community to tropical storms and habitat degradation. Further investigations of this community are necessary to understand how major disturbances affect resilience and long-term viability of colonial waterbird communities on barrier islands.

Breeding Habitat Requirements and Colony Formation by Royal Terns (Thalasseus Maximus) and Sandwich Terns (T. Sandvicensis) on Barrier Islands in the Gulf of Mexico

ABSTRACT. Restoration and maintenance of barrier islands to preserve structural integrity and protect against erosional forces is a common goal of coastal protection. An assessment of restored barrier islands for their suitability as wildlife habitat is crucial for improvement of restoration methods and conservation of barrier-island-dwelling species, especially ground-nesting waterbirds. During the 2008 and 2009 breeding periods, we conducted a quantitative assessment of colonial waterbird use of the Isles Dernieres Barrier Island Refuge (IDBIR), Louisiana, which has experienced several restoration projects since the early 1990s, to understand the breeding ecology of two terns in the genus Thalasseus and investigated why some restored areas have not been colonized. Our objectives were to determine hatching success of the two species, identify important habitat characteristics for their reproduction and colony formation, and evaluate the success of past restoration efforts in providing suitable nesting habitat. Habitat characteristics were important for hatching success, including spatial attributes of nest sites and substrate composition. Discriminant function analysis revealed that suitable habitat for colony formation was available at some inactive restored areas, but the majority of inactive areas were unsuitable. The paucity of nesting activity at potentially suitable restored areas may be attributable to the greater activity of mammalian predators that we detected at inactive areas than at active colony sites. Management of restored barrier islands for specific waterbird habitat requirements, creation of new islands containing suitable ground-nesting habitat, and appropriate control of mammalian predators are critical factors for effective waterbird conservation and ecosystem function in these disturbance-prone regions.

Biogeography of the birds of the Bahamas with special reference to the island of San Salvador

Abstract We used original data (mist net captures) from San Salvador and Andros Island and literature sources for 19 islands in the Bahamas to conduct a biogeographic analysis of the permanent resident, terrestrial bird communities in the archipelago. The number of regularly occurring resident species on the 19 islands varied between 6 and 35 species. Island area accounted for 76% of the variation in richness, but multivariate analyses showed that vegetation and topography also affected richness: the richest communities were found on large islands that were dominated by pines and which had the highest topographic relief. Separate analyses of raptors, pigeons and doves, near-passerines, and passerines confirmed the primacy of island area as a determinant of richness among all groups except passerines. Among the latter species, area effects were secondary to vegetation type and elevation. The number of bird species on San Salvador conformed closely to the number predicted based on island area alone, but habitat use by the current avian community is at odds with the taller broadleaf forests that covered most of the island little more than 300 yr ago. We suspect that San Salvador has experienced numerous extinctions since that time.

Hatching Success and Nest Site Characteristics of Black Skimmer (Rynchops niger) on the Isles Dernieres Barrier Island Refuge, Louisiana

Abstract. Barrier islands provide numerous ecosystem functions and services, including critical breeding habitat for many waterbird species. Louisianas barrier islands are experiencing rapid land loss and habitat degradation. Restoration of barrier islands has become a high priority in Louisiana and barrier island degradation has increased waterbird reliance on restored dredge material islands. To improve restoration and management of barrier islands, we investigated the hatching success of Black Skimmer (Rynchops niger) and determined important habitat characteristics for their hatching success. Nest monitoring and nest habitat characteristics were measured at breeding colonies on the Isles Dernieres Barrier Island Refuge, Louisiana, in 2009 and 2010. Hatching success varied greatly for Black Skimmers (1–84%). Predation, flooding, and competition were the three main causes of nest failure. Habitat modeling identified nest elevation relative to the high-tide line and distance to high-tide line as important habitat characteristics. Continued restoration to build landmass on the islands is necessary to maintain quality nesting areas for Black Skimmers. Additionally, dredge applications to increase elevation, vegetation management, and predator control can provide more quality habitat and increase hatching success.

Productivity and Chick Growth Rates of Royal Tern (Thalasseus maximus) and Sandwich Tern (Thalasseus sandvicensis) on the Isles Dernieres Barrier Island Refuge, Louisiana

Abstract. Barrier islands in Louisiana and elsewhere in the northern Gulf of Mexico region provide valuable breeding habitat for numerous waterbird species; however, these islands are also deteriorating at an alarming rate. Management and conservation of waterbird species in these dynamic environments require a better understanding of the breeding biology for northern Gulf of Mexico populations. Productivity parameters were investigated for Royal (Thalasseus maximus) and Sandwich (T. sandvicensis) terns at the Isles Dernieres Barrier Island Refuge in Terrebonne Parish, Louisiana, during the 2009 and 2010 breeding seasons. Mean hatching success for Royal Tern was 77% (n = 169 nests), while Sandwich Tern hatching success was 75% (n = 130 nests). For both Royal and Sandwich terns, the estimated probability that a chick survived from hatching to fledging age was 55% (n = 630 nestlings). Overall, estimated breeding success for Royal and Sandwich terns was 42.3% and 41%, respectively. Chick growth rates were similar for both species and among islands, suggesting similar habitat quality among islands of Isles Dernieres Barrier Island Refuge. Growth rates (K) for both Royal and Sandwich terns were greatest for tarsus (K = 0.194 and K = 0.184, respectively), followed by mass (K = 0.143 and K = 0.164, respectively), and then wing cord (K = 0.125 and K = 0.110, respectively). Future studies evaluating causes of chick mortality would provide insight into the quality of habitat provided during this life stage. Chick growth rates may also be a useful indicator of ecological change and response to disturbances such as the Deepwater Horizon oil spill.