Browsing by Author "Jaime A. Collazo, Committee Chair"

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Assessing the Effects of Scale and Habitat Management on the Residency and Movement Rates of Migratory Shorebirds at the Tom Yawkey Wildlife Center, South Carolina.
(2007-12-17) Obernuefemann, Kelsey Piper; Jaime A. Collazo, Committee Chair; James E. Lyons, Committee Member; Kenneth H. Pollock, Committee Member; Theodore R. Simons, Committee Member
I evaluated the influence of inter-wetland distance and the timing of drawdowns on local daily survival (residency) and movement probability of Semipalmated Sandpipers (Calidris pusilla) during the springs of 2006 and 2007 at the Tom Yawkey Wildlife Center (YWC), South Carolina. There is growing interest in determining the scale at which coastal wetlands are functionally connected and how management influences their use by migrant shorebirds. Parameters of interest were estimated using multi-state models and encounter histories obtained from resight and telemetry data. Data were collected in the spatial context of three clusters of multiple wetland units each separated by distances of 2.6 to 4.1 km and two hydrologic treatments--a slow and fast draw down. Mean length of stay was 2.99 d (95% CIs = 2.45 - 3.52) in 2006 and 4.57 d (95% CIs = 2.59 — 8.92) in 2007. Residency probability was influenced by a negative and significant interaction between estimated percent fat at capture and southerly wind speed. This meant that differences in departure rates by birds with varying body conditions were minimized. Sixty-five percent of all marked birds stayed within 2 km from their banding location. Movement probabilities were negatively related to inter-cluster distance and bird density. In the spatial context of YWC there was functional connectivity among the clusters that were ˜2.5 km apart; movement was negligible between units at nearly twice that distance (4.1 km). Contrary to expectations, the average probability of surviving and not moving for birds in slow-managed units was higher than birds in fast-managed units (PhiSS 2006 = 0.488, PhiSS 2007 = 0.654). On average, birds marked in fast-managed units moved out at high rates (Psi 2006 = 0.399, Psi 2007 = 0.467). Higher prey biomass and bird density in slow-managed units influenced observed residency and movement rates. My findings advocate for conservation strategies that identify functionally connected wetland units and suggested that habitat supplementation for shorebirds during peak migration can be met by carefully planned staggered, slow drawdowns. The effectiveness of fast drawdowns is vulnerable to differential prey base quality, presence of birds on previously exposed habitat, failure of water control structures to operate properly, and the possibility of mismatching peak migration and rapid drawdown implementation.
Avian conservation in north-central Puerto Rico: Assessing the conservation value of shaded coffee plantations and the influence of nest location and habitat on nest predation rates
(2006-01-23) Gleffe, Jessica Dawn; Jaime A. Collazo, Committee Chair; James F. Gilliam, Committee Member; Kenneth H. Pollock, Committee Member
As size and number of undisturbed forests dwindle due to human encroachment, the importance of disturbed areas, such as secondary forests and shaded coffee plantations, for conservation of avifauna has risen. These 'functional substitutions' are not only recognized and valued at present, but in some cases, they may have played important conservation roles in the past. It is hypothesized that shaded coffee plantations in Puerto Rico played such a role by minimizing extinction rates of resident forest avifauna during periods of widespread deforestation during the 19th and 20th centuries. Implicit in this refugia hypothesis is that shaded coffee plantations harbored successful breeding populations. Data to evaluate this possibility, however, were not available. Likewise, data on breeding productivity and other measures of reproduction were not available for secondary forests, which as of 1992 totaled 41% of the island's forest cover. These measures are intimately related to fitness and, therefore, provide a useful basis to guide habitat conservation initiatives and management. In this study, I report on the reproductive activity and productivity of resident avifauna in shaded coffee plantations and compare them with similar data from secondary forests in Puerto Rico from 1997 to 1999. During that period, 253 nests were found in coffee plantations (12 ha) and 97 in secondary forests (45 ha). The composition of resident species found nesting in shaded coffee plantations and secondary forests was similar. Some of the most common nesting species were endemics. Predation and nest abandonment each accounted for 38% of nest failures. Nest success did not differ between secondary forest and shaded coffee plantations for vireos, tanagers, and hummingbirds. Similarly, breeding productivity did not differ between habitat types for four species for which sufficient data were available. Although the fate of fledglings (e.g., dispersal, survival) was not followed, documenting successful reproduction in shaded coffee plantations confirmed a fundamental assumption of the refugia hypothesis. This finding, coupled with the fact that shaded coffee plantations were more widespread in the past and were managed as rustic plantations and traditional polycultures (resembling primary forests), lends considerable support to the notion that shaded coffee plantations have served as a refuge for resident avian species during periods of widespread deforestation. The production capacity of shaded coffee plantations was dependent on nesting substrates provided by the shade vegetation (canopy) layer, not the coffee tree layer. Nesting activity in secondary forests also occurred primarily in the canopy layer. To investigate the basis of this pattern, I tested whether the observed nesting patterns were influenced by differential predation pressure between the understory and canopy layers. I also tested whether predation pressure differed between canopy layers of plantations and secondary forests to further assess the conservation value of shaded plantations. Tests were conducted using a series of carefully designed artificial nest experiments during the breeding season of 2005. I found that predation rates ranged from 0.44 to 0.77 (average = 0.65 ± 0.06 SE) for understory and from 0.45 to 0.80 (average = 0.65 ± 0.05 SE) for canopy nest heights. Predation rates ranged from 0.67 to 1.0 (average = 0.84 ± 0.06 SE) in shaded coffee plantations, and from 0.63 to 0.97 (average = 0.81 ± 0.06 SE) in adjacent secondary forest. Rates for both experiments were not significantly different (P > 0.05). Based on photographic evidence, avian and mammalian nest predators can prey upon nests regardless of height. Experiments and data from natural nests suggest that birds nesting in shaded plantations are not at a disadvantage compared to those nesting in secondary forests. Moreover, the pervasive nature of nest predation reported in this work, and its influence on habitat quality, affirmed the need to identify and manage habitat features associated with nest success.
Population Viability Analysis of Puerto Rican Parrots: an assessment of its current status and prognosis for recovery.
(2003-06-20) Muiznieks, Britta Dace; Jaime A. Collazo, Committee Chair
Despite 34 years of recovery efforts, the Puerto Rican Parrot continues to face a high risk of extinction. In 2002 the population count was estimated at 20-24 individuals, similar to post-hurricane Hugo counts (23) and close to the all time low count of 17-19 individuals in 1973. In light of this situation, coupled with discussions about establishing a second population in the karst region in north-central Puerto Rico, I reviewed cumulative demographic data collected over the past 13 years and conducted a population viability analysis to update the status and recovery outlook of the species. I used program Vortex to assess the status of the species and conducted a sensitivity analysis to assess the relative importance of selected parameters in the demography of the species. Basic Scenario model projections over 100 years were of a declining population (stoc. r = -0.066). Within 10 years the mean population (across extant populations) dropped from 40 to 24 individuals, and within 20 years, to 15 individuals. The persistence of the population was 0 and the mean time to extinction was 37.4 years. Sensitivity analyses indicated that almost none of the parameter values used in the model scenarios yielded a positive, mean stochastic growth. Low juvenile mortality (32% for age 0-1) produced the only positive average stochastic growth rate (r>0.02). Relative to the Basic Scenario model, the population grew only when productivity levels exceeded 2.5. Productivity levels recorded from 1990-95 (1.88 young fledged/active nest) and 1996-2002 (1.23young fledged/active nest) resulted in a steady population decline with very low persistence (0-3%). At the average productivity since 1990 (1.56 young fledged /active nest), supplementation temporarily boosted the mean population size. Once supplementations stopped, mean population size declined. The population continued to grow only when supplementation was coupled with sustained high productivity (e.g., 2.75 young fledged /active nest). To augment the knowledge base of resident avifauna in north-central Puerto Rico, I collected information on the general biology of the Puerto Rican Woodpecker. The biology of the species was poorly documented, and its nesting habits might provide insights into what Puerto Rican Parrots may face when released in the region. Woodpecker detections were consistently higher in lower montane/shaded coffee plantation sites when compared to sites in karst topography. Management, past and present, in shaded coffee plantations may help explain the high number of detections in shaded coffee sites as compared to secondary forests. Management results in higher numbers of dead trees as trees are girdled routinely to 'create openings' in the shade. The onset of reproduction during my study was in January, with the majority of incubation occurring in February and March. The average observed clutch size was 5 eggs (n=6, SE=0.26), with only one cavity containing 4 eggs. Nest success varied greatly from year to year. In 1998, only 1 out of 7 active nests successfully fledged young, whereas in 1999, 7 out of 9 did so. Possible explanations for high chick mortality, particularly in 1998, were infestation of chicks with ectoparasites or dehydration and/or hyperthermia. There is no evidence, from this study or from literature, to believe that the status of the Puerto Rican Woodpecker is in danger. The value of this study lies primarily on augmenting the knowledge about the natural history of another endemic species.