Springing forward: Migrating songbirds catch up with the start of spring in North America.

In temperate regions, the annual pattern of spring onset can be envisioned as a 'green wave' of emerging vegetation that moves across continents from low to high latitudes, signifying increasing food availability for consumers. Many herbivorous migrants 'surf' such resource waves, timing their movements to exploit peak vegetation resources in early spring. Although less well studied at the individual level, secondary consumers such as insectivorous songbirds can track vegetation phenology during migration as well. We hypothesized that four species of ground-foraging songbirds in eastern North America-two warblers and two thrushes-time their spring migrations to coincide with later phases of vegetation phenology, corresponding to increased arthropod prey, and predicted they would match their migration rate to the green wave but trail behind it rather than surfing its leading edge. We further hypothesized that the rate at which spring onset progresses across the continent influences bird migration rates, such that individuals adjust migration timing within North America to phenological conditions they experience en route. To test our hypotheses, we used a continent-wide automated radio telemetry network to track individual songbirds on spring migration between the U.S. Gulf Coast region and northern locations closer to their breeding grounds. We measured vegetation phenology using two metrics of spring onset, the spring index first leaf date and the normalized difference vegetation index (NDVI), then calculated the rate and timing of spring onset relative to bird detections. All individuals arrived in the southeastern United States well after local spring onset. Counter to our expectations, we found that songbirds exhibited a 'catching up' pattern: Individuals migrated faster than the green wave of spring onset, effectively closing in on the start of spring as they approached breeding areas. While surfing of resource waves is a well-documented migration strategy for herbivorous waterfowl and ungulates, individual songbirds in our study migrated faster than the green wave and increasingly caught up to its leading edge en route. Consequently, songbirds experience a range of vegetation phenophases while migrating through North America, suggesting flexibility in their capacity to exploit variable resources in spring.

En las regiones templadas, el patrón anual de inicio de la primavera puede concebirse como una "ola verde" de vegetación emergente que se desplaza por los continentes desde las latitudes bajas a las altas, lo que significa una mayor disponibilidad de alimento para los consumidores. Muchos herbívoros migratorios "surfean" estas olas de recursos, programando sus movimientos para aprovechar los picos de vegetación a principios de primavera. Aunque menos estudiados a nivel de individuo, los consumidores secundarios, como las aves terrestres insectívoras, también pueden seguir la fenología de la vegetación durante la migración. Hipotetizamos es que cuatro especies de aves terrestres que se alimentan en el suelo en el este de Norteamérica - dos reinitas y dos zorzales - programan sus migraciones primaverales para que coincidan con las fases más tardías de la fenología de la vegetación, que se corresponden con un aumento de artrópodos, y predijimos que sincronizarian su ritmo de migración con la ola verde, pero que irían detrás de ella en lugar de surfear su borde delantero. También hipotetizamos que el ritmo al que avanza la primavera en el continente influye en las tasas de migración de las aves, de modo que los individuos ajustan la fecha de migración dentro de Norteamérica a las condiciones fenológicas que experimentan en ruta. Para comprobar nuestras hipótesis, utilizamos una red automatizada de radiotelemetría a escala continental para seguir individuos en su migración primaveral entre la región de la costa del Golfo de EEUU y las localidades septentrionales más cercanas a sus zonas de cría. Medimos la fenología de la vegetación utilizando dos métricas del inicio de la primavera, el índice de la fecha de la primera hoja primaveral y el índice de vegetación de diferencia normalizada (NDVI), luego calculamos la tasa y el tiempo de la aparaciòn de la primavera relativo a las detecciones de aves. Todos los individuos llegaron al sureste de EEUU bastante después del inicio de la primavera local. Contrario a nuestras expectativas, descubrimos que las aves terrestres mostraron un patrón de Carrera para "ponerse al día": los individuos migraron frente a la ola verde del inicio de la primavera, acercándose efectivamente al inicio de la primavera a medida que llegaban a las zonas de cría. Mientras que el surfing de las olas de recursos es una estrategia migratoria bien documentada para las aves acuáticas herbívoras y los ungulados, los individuos de aves terrestres de nuestro estudio migraron más rápido que la ola verde y alcanzaron cada vez más el borde delantero en ruta. En consecuencia, las aves terrestres experimentan una serie de fases fenológicas de la vegetación mientras migran a través de Norteamérica, lo que sugiere flexibilidad en su capacidad para explotar recursos variables en primavera.

Cementless total hip replacement in an alpaca.

OBJECTIVE: To report management of a chronic slipped capital femoral epiphysis (SCFE) in an alpaca using cementless total hip replacement (THR). STUDY DESIGN: Case report. ANIMAL: An 18-month-old, 47 kg alpaca male. METHODS: Cementless THR was performed in an alpaca with a chronic, right SCFE, and secondary osteoarthritis. Force plate gait analysis was performed before and 8 weeks after surgery. Outcome was determined through clinical evaluation, radiography, and force plate gait analysis. RESULTS: Cementless THR resulted in marked improvement in the alpaca's comfort level, degree of lameness, and range of motion. On preoperative force plate gait analysis there was decreased contact time (P=.01) and vertical impulse (P<.01) of the affected limb, whereas at 8 weeks postoperatively significant differences in gait analysis between pelvic limbs were not apparent. CONCLUSION: THR using a BioMedtrix canine cementless modular prosthesis restored hip function in an alpaca with coxofemoral osteoarthritis from chronic SCFE. CLINICAL RELEVANCE: THR may be an appropriate treatment for selected traumatic and degenerative conditions of the coxofemoral joint in alpacas.

Effect of cell physicochemical characteristics and motility on bacterial transport in groundwater.

The influence of physicochemical characteristics and motility on bacterial transport in groundwater were examined in flow-through columns. Four strains of bacteria isolated from a crystalline rock groundwater system were investigated, with carboxylate-modified and amidine-modified latex microspheres and bromide as reference tracers. The bacterial isolates included a gram-positive rod (ML1), a gram-negative motile rod (ML2), a nonmotile mutant of ML2 (ML2m), and a gram-positive coccoid (ML3). Experiments were repeated at two flow velocities, in a glass column packed with glass beads, and in another packed with iron-oxyhydroxide coated glass beads. Bacteria breakthrough curves were interpreted using a transport equation that incorporates a sorption model from microscopic observation of bacterial deposition in flow-cell experiments. The model predicts that bacterial desorption rate will decrease exponentially with the amount of time the cell is attached to the solid surface. Desorption kinetics appeared to influence transport at the lower flow rate, but were not discernable at the higher flow rate. Iron-oxyhydroxide coatings had a lower-than-expected effect on bacterial breakthrough and no effect on the microsphere recovery in the column experiments. Cell wall type and shape also had minor effects on breakthrough. Motility tended to increase the adsorption rate, and decrease the desorption rate. The transport model predicts that at field scale, desorption rate kinetics may be important to the prediction of bacteria transport rates.

Bacterial transport experiments in fractured crystalline bedrock.

The efficiency of contaminant biodegradation in ground water depends, in part, on the transport properties of the degrading bacteria. Few data exist concerning the transport of bacteria in saturated bedrock, particularly at the field scale. Bacteria and microsphere tracer experiments were conducted in a fractured crystalline bedrock under forced-gradient conditions over a distance of 36 m. Bacteria isolated from the local ground water were chosen on the basis of physicochemical and physiological differences (shape, cell-wall type, motility), and were differentially stained so that their transport behavior could be compared. No two bacterial strains transported in an identical manner, and microspheres produced distinctly different breakthrough curves than bacteria. Although there was insufficient control in this field experiment to completely separate the effects of bacteria shape, reaction to Gram staining, cell size, and motility on transport efficiency, it was observed that (1) the nonmotile, mutant strain exhibited better fractional recovery than the motile parent strain; (2) Gram-negative rod-shaped bacteria exhibited higher fractional recovery relative to the Gram-positive rod-shaped strain of similar size; and (3) coccoidal (spherical-shaped) bacteria transported better than all but one strain of the rod-shaped bacteria. The field experiment must be interpreted in the context of the specific bacterial strains and ground water environment in which they were conducted, but experimental results suggest that minor differences in the physical properties of bacteria can lead to major differences in transport behavior at the field scale.