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This title compares and contrasts the ruby-throated hummingbird's appearance, behavior, habitat, and life cycle to other birds like the Austrian pelican and the turkey vulture.

The diversification of hummingbirds (Trochilidae) has shaped the pollination strategies and floral trait evolution in at least 68 families of flowering plants in the Western Hemisphere. The trumpet creeper (Bignoniaceae) is the quintessential example of ornithophily in eastern North America. The mutualistic relationship between this orange‐flowered liana and the ruby‐throated hummingbird (Archilochus colubris) was illustrated as early as 1731. However, neither historical nor modern accounts accurately describe the feeding behavior of ruby‐throats at trumpet creeper flowers or the floral adaptations for ornithophily. This paper explores their surprisingly immersive mode of foraging at trumpet creeper flowers and quantitatively assesses floral traits in two populations in the Ozark Mountains. The ruby‐throat's bill is approximately one‐third the length of the trumpet‐shaped flowers, which counters the tendency for the corolla length of ornithophilous plants to match the bill length of their principal hummingbird pollinator. To access the nectary, ruby‐throats grasp or cling to the ventral petal lobe of the corolla with their claws and thrust their head and upper body into the flower. This immersive “floral‐diving” had not been formally documented among the 356 species of hummingbirds until now. The didynamous anthers and stigma are strategically positioned inside the corolla to brush the crown feathers when the ruby‐throat inserts its head. A narrow stricture in the corolla, about a third of the way up, allows the bill and tongue of hummingbirds to pass while blocking bumblebees and carpenter bees from reaching the nectary. As a result, the abundant sucrose‐rich floral nectar seems to be reserved for hummingbird pollinators. The trumpet creeper (Campsis radicans) is the prime example of ornithophily in eastern North America. This paper describes the unique foraging behavior of its principal pollinator, the ruby‐throated hummingbird (Archilochus colubris), and presents a quantitative analysis of floral adaptations for ornithophily in the Ozark Mountains.

Although the breeding ranges of Archilochus alexandri (Black-chinned Hummingbird) and Archilochus colubris (Ruby-throated Hummingbird) are narrowly parapatric in central Texas and central and southern Oklahoma, there have been few reports of hybridization in the literature and no well-documented hybrid specimens. Here we provide a comprehensive assessment of two male hybrids collected, respectively, in Grayson County, Texas, and East Baton Rouge Parish, Louisiana. As has been the pattern in other hummingbird hybrids, both specimens exhibit a blended mosaic of plumage characters of the parental species. Sequence for mitochondrial cytochrome c oxidase subunit 1 (CO1) for the hybrid specimen from East Baton Rouge Parish (LSU 182,831) confirms A. colubris as the female parent.

We assessed the feasibility of marking ruby-throated hummingbirds (Archilochus colubris) with radio frequency identification (RFID) tags. We trapped 27 hummingbirds at feeding stations on a 2.0-ha study site. We subcutaneously implanted each hummingbird with a 0.067-g RFID tag and released it at the capture site. We deployed RFID transceiver systems at 5 feeding stations and electronically monitored tagged hummingbird activity continuously on the study site through 3 summers. Post-release relocation rate exceeded expectations based on previous leg band recovery data, and bird activity data acquisition was consistent and reliable and required minimum labor.

Surprisingly little is known about the migration and stopover biology of Ruby-throated Hummingbirds (Archilochus colubris), and even less is known about their sex- or age-dependent migration. First, we provide basic information on the migration and stopover biology of this species along the northern coast of the Gulf of Mexico during autumn, including phenology, stopover duration, fuel deposition rate (FDR), arrival mass, and estimated flight ranges. Second, we investigate whether these stopover variables are influenced by age or sex. Age-dependent migration is expected because young, hatch-year birds on their first migration lack the experience of older individuals. Sex-dependent migration is expected because of sexually dimorphic characteristics in wing morphology and body size. We obtained information on arrival mass, phenology, FDR, stopover duration, and estimated flight ranges through banding data, passive integrated transponder tags, radio telemetry, and color marking at a long-term migration station along the northern coast of the Gulf of Mexico. Our data provide strong evidence for age-dependent migration and only weak evidence for sex-dependent migration. Older birds arrived earlier, had larger fuel loads, and had shorter stopover durations than younger birds. In younger birds, we found no effect of sex on FDR, arrival mass, stopover duration, or phenology. Older males arrived with larger fuel loads than females. Finally, we used flight simulation software and our data to estimate that males and older birds were capable of longer potential flight ranges than either females or younger birds.

Many small endotherms use torpor to reduce metabolic rate and manage daily energy balance. However, the physiological ‘rules’ that govern torpor use are unclear. We tracked torpor use and body composition in ruby-throated hummingbirds ( Archilochus colubris ), a long-distance migrant, throughout the summer using respirometry and quantitative magnetic resonance. During the mid-summer, birds entered torpor at consistently low fat stores (~5% of body mass), and torpor duration was negatively related to evening fat load. Remarkably, this energy emergency strategy was abandoned in the late summer when birds accumulated fat for migration. During the migration period, birds were more likely to enter torpor on nights when they had higher fat stores, and fat gain was positively correlated with the amount of torpor used. These findings demonstrate the versatility of torpor throughout the annual cycle and suggest a fundamental change in physiological feedback between adiposity and torpor during migration. Moreover, this study highlights the underappreciated importance of facultative heterothermy in migratory ecology. Torpor is an energy-saving strategy used by warm-blooded animals, including birds and small mammals. Similar to hibernation, although shorter in duration, torpor is a state of minimal activity, low body temperatures and reduced metabolism that helps animals conserve energy in unfavorable conditions. Some animals use torpor to survive times when food is not readily available. Hummingbirds, for example, eat nectar all day long to meet their high energy needs, but must build fat reserves to see them through their overnight fast. If they go to sleep with too little fat, they can descend into torpor to stretch out that limited energy supply and survive until morning. Many hummingbirds migrate to areas with warmer weather, where food remains available, for the winter months. The ruby-throated hummingbird ( Archilochus colubris ), for example, travels over 5,000 kilometers in its fall migration. Like most long-distance migrants, ruby-throated hummingbirds increase their fat stores before departing, using these stores to fuel their journey. It is thought that this bird may use torpor as a way to accelerate fat build up before its annual migration. However, it remained unclear whether hummingbirds switched from using torpor strictly in energy emergencies, to using it as strategy to prepare for migration. To shed light on this question, Eberts, Guglielmo and Welch investigated when, why and how hummingbirds save energy using torpor during the summer, and whether there are seasonal shifts in their use of torpor coinciding with migration. Eberts, Guglielmo and Welch hypothesized that a bird would initiate daily torpor if its energy stores fall below a critical level during the night, but that they may abandon this threshold (triggering torpor at higher fat levels) in late summer as a way to spare energy and gain fat before their annual migration. To test their hypotheses, Eberts, Guglielmo and Welch tracked body composition, food intake, energy expenditure and torpor use throughout summer in a group of captive ruby-throated hummingbirds. In the middle of the summer, the birds entered torpor and remained torpid for longer when they went to sleep with low fat stores. In late summer, however, the same birds were more likely to enter torpor at consistent times and when they had higher fat stores. Eberts, Guglielmo and Welch also observed that the more time birds spent in torpor, the more fat they gained. This suggests that in late summer, hummingbirds switch from using torpor as a survival strategy to using it to maximize energy savings before migration. These results clearly define the physiological rules governing torpor use in hummingbirds. They also support the long-standing assumption that torpor helps migratory species save energy and accumulate fat stores before long-haul flights.

Knowledge of spatial connectivity between breeding and non-breeding locations of migratory birds and their breeding site fidelity are important for avian conservation. Ruby-throated Hummingbirds (RTHU, Archilochus colubris ) breed in eastern Canada west to the Rocky Mountains and in the USA east of the Mississippi River and spend the non-breeding period in Mexico, Central America, and southern Florida, USA. We measured the hydrogen and oxygen stable isotopic compositions of adult RTHU tailfeathers (fourth rectrix) from three breeding locations in North America to estimate migratory connectivity between breeding and non-breeding grounds where feathers are grown. Feather δ 2 H values showed no statistical difference among the three sampling locations as well as disparate geographic assignments from one location on the non-breeding grounds in Costa Rica. Therefore, only weak evidence of migratory connectivity between breeding and non-breeding grounds could be ascertained for our sample of this species. The lack of migratory connectivity detected for Ruby-throated Hummingbirds using stable isotopes is consistent with origins from broad regions on the non-breeding grounds. However, it may also imply that precipitation δ 2 H values on the non-breeding grounds do not vary enough to detect a difference among our study populations. Sampling of additional populations in the eastern and southern portion of the species’ breeding range and the non-breeding grounds may reveal differences in migratory connectivity among populations and requires further investigation. The δ 18 O values of feathers correlated poorly to their δ 2 H values, an effect that may reflect the balance between metabolically driven processes and environmental water on the δ 18 O values of hummingbird tissues. This study provides the foundations for further investigations into migratory connectivity of RTHU using δ 2 H f values and suggests potential avenues of study for use of δ 18 O values of tissues in metabolic research.

Phenological patterns in birds appear to be temperature-dependent in part, and global temperatures are undergoing change. Many studies of bird phenology are conducted at broad temporal but local spatial scales, making it difficult to assess how temperature affects bird migration across landscapes. Recently, networks of “citizen science” volunteers have emerged whose collective efforts may improve phenology studies as biases associated with such efforts are recognized and addressed. We compared mean Rubythroated Hummingbird (Archilochus colubris) first arrival dates from Journey North (2001–2010) with data from the North American Bird Phenology Program (1880–1969). Ruby-throated Hummingbirds arrived earlier in the more recent period throughout the eastern United States; these advances, however, varied by latitude from 11.4 to 18.2 days, with less pronounced changes above 41°N. Warmer winter and spring temperatures in North American breeding grounds were correlated with earlier arrivals at lower latitudes in our recent period. Surprisingly, Ruby-throated Hummingbirds arrived later at high latitudes (42–43°N) during warmer winters and later at both mid- and high latitudes (38–39, 41–44°N) during warmer springs, which perhaps indicates extended migratory stopovers below 40°N during these years. Overall, weather variables predicted arrival dates better in the recent than in the historical period. Our results document spatial variability in how warming temperatures affect hummingbird arrivals and add credence to the hypothesis that spatial differences in arrival patterns at high versus low latitudes could exacerbate asynchrony between some birds and their food resources and modify associated ecosystem services such as pollination and insect pest suppression.

Radiotelemetry has advanced the field of wildlife biology, especially with the miniaturization of radio-tags. However, the major limitation when radio-tagging birds is the size of the animal to which a radio-tag can be attached. We tested how miniature radio-tags affected flight performance and behavior of Ruby-throated Hummingbirds (Archilochus colubris), possibly the smallest bird species that has been fitted with radio-tags. Using eyelash adhesive, we fitted hatch-year individuals (n = 20 males, n = 15 females) with faux radio-tags of 3 sizes that varied in mass and antenna length (220 mg, 12.7 cm; 240 mg, 12.7 cm; and 220 mg, 6.35 cm), then filmed the birds in a field aviary to quantify activity budgets. We also estimated flight range using flight simulation models. When the 3 radio-tag packages were pooled for analysis, the presence of a radio-tag significantly decreased both flight time (∼8%) and modeled flight range (∼23%) in comparison to control birds. However, a multiple-comparison analysis between the different packages revealed that there was a significant difference in flight time when the larger radio-tag package (240 mg) was attached, and no significant difference in flight time when the lighter radio-tag packages (220 mg) were attached. Our results are similar to those of other studies that analyzed the flight time or flight range of birds wearing radio-tags. Therefore, currently available lightweight radio-tags (≤220 mg) may be a new option to aid in the study of hummingbird biology. Future study should focus on the additional drag created by the radio-tag and the effects of the lightest radio-tag packages on free-ranging birds. These studies would provide additional information to determine the feasibility of the use of radio-tags to study hummingbird biology.

Global change can affect several aspects of bird biology, including population size and migration timing. We used count data collected during 25 years (1990–2014) at Hawk Mountain Sanctuary, a raptor migration watch-site in eastern Pennsylvania, to investigate population changes in Ruby-throated Hummingbirds (Archilochus colubris) and the timing of their autumn migration, in light of ongoing climate change. Hummingbird numbers increased significantly from 1990–2014. The first 5%-, 50%-, 95%- and average passage dates of hummingbirds over this time indicated an earlier passage, with the first 5% passage-date shifting earlier significantly. Passage duration (number of days between 5% and 95% of the flight) remained relatively constant from 1990–2014. In light of similar shifts in timing of spring passage of this species, our results suggest that Ruby-throated Hummingbirds may be shifting the timing of their migratory cycle.