Non-migrating Birds Research Articles

Night Migratory Songbirds Exhibit Metabolic Ability to Support High Aerobic Capacity during Migration.

Aerobic metabolism in night migratory songbirds exhibit seasonal plasticity, which depends not only on annual life history stages (LHSs), viz., migratory/nonmigratory or breeding/nonbreeding, but also on the time of the day. Initially, we studied daily changes in behavior/physiology alongside aerobic metabolism intermediates using gas chromatography–mass spectrometry-based chemometric analyses of serum of migratory male redheaded buntings during low-energy wintering, that is, the nonmigrating LHS. Then, the metabolic phenotype of nonmigrating birds was compared with that of photostimulated migrating buntings, the latter representing the high-energy LHS. Diurnal changes such as daytime feeding and activity were reflected by increased fatty acid (FA, viz., palmitic, oleic, and linoleic acids) levels and protein catabolites, whereas higher night-time levels of short-chain FAs indicated lipolysis in night-fasted birds. High night-time levels of taurine, a sulfur amino acid, suggested the endogenous metabolite rendering an adaptive advantage to hyperglycaemic night migratory songbirds during the LHS with low daily energy expenditure. Conversely, migrating birds, largely night-active, exhibited higher circulatory FA, its mobilization, and increased aerobic catabolism, and the adipocyte-secreted lipid, palmitoylethanolamide (PEA), capable of activating the peroxisome proliferator-activated receptor α–PGCα axis, showed elevated levels throughout the day. PEA is known for anti-inflammatory and cannabinomimetic properties, and we show, for the first time, circadian changes in PEA levels in any migrating bird. Significantly higher levels of pyridoxal phosphate also suggested the bird’s protective ability to combat metabolic stress through high aerobic capacity during migration. This study elucidates putative “serum biomarkers” with a protective role in stress accrued by enhanced aerobic capacity requirements at the organismal level.

The threat of global mercury pollution to bird migration: potential mechanisms and current evidence.

Mercury is a global pollutant that has been widely shown to adversely affect reproduction and other endpoints related to fitness and health in birds, but almost nothing is known about its effects on migration relative to other life cycle processes. Here I consider the physiological and histological effects that mercury is known to have on non-migrating birds and non-avian vertebrates to identify potential mechanisms by which mercury might hinder migration performance. I posit that the broad ability of mercury to inactivate enzymes and compromise the function of other proteins is a single mechanism by which mercury has strong potential to disrupt many of the physiological processes that make long-distance migration possible. In just this way alone, there is reason to expect mercury to interfere with navigation, flight endurance, oxidative balance, and stopover refueling. Navigation and flight could be further affected by neurotoxic effects of mercury on the brain regions that process geomagnetic information from the visual system and control biomechanics, respectively. Interference with photochemical reactions in the retina and decreases in scotopic vision sensitivity caused by mercury also have the potential to disrupt visual-based magnetic navigation. Finally, migration performance and possibly survival might be limited by the immunosuppressive effects of mercury on birds at a time when exposure to novel pathogens and parasites is great. I conclude that mercury pollution is likely to be further challenging what is already often the most difficult and perilous phase of a migratory bird's annual cycle, potentially contributing to global declines in migratory bird populations.

Role of wild birds as carriers of multi-drug resistant Escherichia coli and Escherichia vulneris.

Emergence and distribution of multi-drug resistant (MDR) bacteria in environments pose a risk to human and animal health. A total of 82 isolates of Escherichia spp. were recovered from cloacal swabs of migrating and non-migrating wild birds. All bacterial isolates were identified and characterized morphologically and biochemically. 72% and 50% of isolates recovered from non-migrating and migrating birds, respectively, showed positive congo red dye binding (a virulence factor). Also, hemolysin production (a virulence factor) was showed in 8% of isolates recovered from non-migrating birds and 75% of isolates recovered from migrating birds. All isolates recovered from non-migrating birds were found resistant to Oxacillin while all isolates recovered from migrating birds demonstrated resistance to Oxacillin, Chloramphenicol, Oxytetracycline and Lincomycin. Some bacterial isolates recovered from non-migrating birds and migrating birds exhibited MDR phenotype. The MDR isolates were further characterized by API 20E and 16S rRNA as E. coli and E. vulneris. MDR Escherichia isolates contain ~1-5 plasmids of high-molecular weights. Accordingly, wild birds could create a potential threat to human and animal health by transmitting MDR bacteria to water streams and other environmental sources through their faecal residues, and to remote regions by migration.

Differential Regulation of Adipokines May Influence Migratory Behavior in the White-Throated Sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

Seasonal differences in behavior patterns of the migratory white-throated sparrow

Avian migration and associated changes in behavior patterns occur on a seasonal basis and are regulated by both circadian and circannual clocks. It is well known that seasonally migrating birds must alter the temporal partitioning of behaviors in order to successfully complete nocturnal migration, although the precise changes in allocation have not previously been examined. Because of the difficulties related to the study of bird migration in the wild, many studies regarding the physiology of migration have been performed in captivity, where nocturnal migratory restlessness is readily observable at the appropriate times of the year. Even so, quantifying the amount and timing of daily behavioral rhythms in migrating and non-migrating individuals has not previously been performed. We used video recordings of a common nocturnal migrant, the white-throated sparrow (Zonotrichia albicollis), to generate a basic ethogram and to chart the timing and frequency of occurrence of each behavior in order to compare migrant individuals with non-migrating birds. Our study suggests that the specific allocation of behaviors are altered during migration and that these changes might contribute to the development of the “migratory syndrome”.

Activation Changes in Zebra Finch (Taeniopygia guttata) Brain Areas Evoked by Alterations of the Earth Magnetic Field

Many animals are able to perceive the earth magnetic field and to use it for orientation and navigation within the environment. The mechanisms underlying the perception and processing of magnetic field information within the brain have been thoroughly studied, especially in birds, but are still obscure. Three hypotheses are currently discussed, dealing with ferromagnetic particles in the beak of birds, with the same sort of particles within the lagena organs, or describing magnetically influenced radical-pair processes within retinal photopigments. Each hypothesis is related to a well-known sensory organ and claims parallel processing of magnetic field information with somatosensory, vestibular and visual input, respectively. Changes in activation within nuclei of the respective sensory systems have been shown previously. Most of these previous experiments employed intensity enhanced magnetic stimuli or lesions. We here exposed unrestrained zebra finches to either a stationary or a rotating magnetic field of the local intensity and inclination. C-Fos was used as an activity marker to examine whether the two treatments led to differences in fourteen brain areas including nuclei of the somatosensory, vestibular and visual system. An ANOVA revealed an overall effect of treatment, indicating that the magnetic field change was perceived by the birds. While the differences were too small to be significant in most areas, a significant enhancement of activation by the rotating stimulus was found in a hippocampal subdivision. Part of the hyperpallium showed a strong, nearly significant, increase. Our results are compatible with previous studies demonstrating an involvement of at least three different sensory systems in earth magnetic field perception and suggest that these systems, probably less elaborated, may also be found in nonmigrating birds.

From the Tundra to Tierra del Fuego: Protecting Key Sites for Birds in Canada and throughout the Western Hemisphere

Canada provides habitat for more than 470 species of migrating and non-migrating birds. They provide a number of ecosystem services; biological control, pollination, seed dispersal, seed germination and nutrient recycling. However their habitats are under increasing pressure from threats such as urban expansion, industrial agriculture, logging, mining and pollution. In order to ensure that our migrants return each spring, we must also work to conserve their vital habitat beyond our borders. Birds are important to conserve in their own right as they are an effective indicator taxon for environmental change; they are relatively large and diurnal, birds are close to ubiquitous geographically, are high on the food chain therefore reflecting change in a diversity of organisms and they are relatively long-lived so studies can be conducted over a number of years. Their distribution therefore helps us to identify areas where measures to conserve biodiversity are especially critical. Not all sites can be conserved so Important Bird Areas (IBAs) have been identified which are conservation priorities. Sites selected as IBAs are effective in capturing a high proportion of threatened, endemic and representative wildlife species other than birds.

Phenotypic flexibility of body composition in relation to migratory state, age, and sex in the western sandpiper (Calidris mauri).

We investigated the flexibility of body composition in relation to seasonally variable demands for endurance flight capacity and hyperphagia in a migratory shorebird. Migrating western sandpipers were sampled in spring and fall while refueling at a north temperate stopover and were compared with nonmigrating birds captured at a tropical wintering area in Panama. Sandpipers weighed 25% more at stopover, and nearly 40% of migratory mass increase consisted of lean body components. Most organs and flight muscles were 10%-100% larger during migration, and the greatest relative size increases occurred in the digestive system (including liver). Birds preparing to initiate spring migration from Panama deposited only fat, suggesting that changes in lean body components take place after migration has begun, possibly through training effects. Sex did not influence body composition. Juveniles making their first southward migration were similar to adults in structural size and body mass but had substantially enlarged alimentary tracts. Sandpipers appeared to deposit lean mass during stopover in fall but not in spring. The dramatic enlargement of the digestive system in this small species that makes short flights and fuels frequently contrasts with the reduction of digestive components in larger species that fuel only once or twice by making one or two very long flights to their destination.

Modulation of lipogenic enzymes, fatty acid synthase and Δ 9 -desaturase, in relation to migration in the western sandpiper ( Calidris mauri )

Long-distance migration in birds is characterized physiologically by periods of rapid fattening and lipogenesis, and increased desaturation of fatty acids stored in adipose tissue. We investigated seasonal, age- and sex-related differences in activities of two lipogenic enzymes, fatty acid synthase and delta9-desaturase, in relation to migration in the small, Arctic-nesting western sandpiper (Calidris mauri). Migration, and associated lipogenesis and fattening, involved marked upregulation of these enzymes in this species. However, this increase in enzyme activity was only seen in actively migrating birds during spring migration, when fatty acid synthase and delta9-desaturase levels increased by 53% and 113%, respectively, compared to non-migrating birds. There was no change in fatty acid synthase enzyme activity during the premigration period, even though body mass of adult birds increased significantly during this period. Similarly, there was no increase in delta9-desaturase activity during premigration, despite the fact that birds increase the proportion of monounsaturated fatty acids in their fat stores at this time. We suggest that upregulation of lipogenic enzymes is required to support high rates of mass gain (0.4 g day(-1)) during short (1-4 day) periods at stop-over sites. However, slower rates of mass gain (0.09 g day(-1)) over several weeks prior to migration can be achieved without any increase in tissue-specific enzyme activity.

Phenological Adaptations in Fleshy Vertebrate-Dispersed Fruits of Temperate Plants

The timing of fruit ripening is an important feature of fleshy-fruited vertebrate-dispersed plants in temperate regions. The dominating dispersal agents are birds, of which the majority are migratory. Many of these birds use fleshy fruits as a source of food to build reserves before and during migration, for which reason many plants ripen their fleshy fruits at a time that coincides with the peak of bird abundance in the autumn (Snow and Snow 1988, Debussche and Isenmann 1992, Noma and Yumoto 1997). However, there is variation in this pattern. At an individual species level, variation in fruit ripening may not follow bird abundance patterns (French 1992, Fuentes 1992, Willson and Whelan 1993). Furthermore, many plants produce fleshy fruits before or after the autumn assembly of migrating birds (Eriksson and Ehrlen 1991, White and Stiles 1992). There are at least four possible explanations for such phenological deviations. First, non-migrating birds, or stationary mammals, may be the most important seed dispersers for some species (Eriksson 1994, Traveset and Willson 1997), relaxing the need for a specific timing of fruit ripening. Second, competition among plants for disperser-attraction may have resulted in different strategies of fruit phenology (Thompson and Willson 1979, Stiles 1980, Stapanian 1982). Early maturing fleshy fruits may primarily attract birds that seek quick energy while the birds still rear their young. Fruits ripening late, i.e. after the birds have migrated, instead attract stationary animals during autumn and winter by providing persistent sources of reserve food. This kind of reasoning leads to predictions of phonological trends in nutritional content of fruit pulp: carbohydrate content would decrease during the season whereas lipids and proteins would increase. Moreover, based on considerations of plant recruitment, Stapanian (1982) suggested that species with early ripening fruits would benefit from having many small seeds instead of few large seeds. The reason is that small seeds are more likely to possess delayed germination, disperse in time, which is suitable for plants that due to dispersal by still territorial birds do not reach far from the mother plant. Third, the phenology of fruiting may be constrained by the timing of flowering, and the subsequent time needed for seed development (Primack 1987). A final explanation for a lack of clear phenological patterns of fruit maturation is that these traits may not be amenable to adaptive explanations at all due to phylogenetic inertia (Herrera 1986, Kochmer and Handel 1986, Bremer and Eriksson 1992, Jordano 1995). According to this view, the traits possessed by many extant fleshy fruits evolved under circumstances no longer prevailing, in some genera as far back as during the early Tertiary. Empirical studies aimed at scrutinizing hypotheses on the relationship between fruit traits and phenology have produced conflicting results. The predicted trends in nutritional content have gained limited support from some studies (Herrera 1982, Johnson et al. 1985, Debussche et al. 1987) but not from others (Piper 1986, Eriksson and Ehrlen 1991). For seasonal trends in structural fruit traits there is generally no support (Herrera 1982, Eriksson and Ehrlen 1991), apart from a trend of increasing seed size found by Piper (1986). A conclusion that presently seems most reasonable is that phylogenetic constraints have a strong impact on fleshy fruit traits, limiting the scope for finding close connections between the traits and features of the present-day environments (Herrera 1995, Jordano 1995). However, no study has explicitly examined structural and nutritional features of fleshy fruits in relation to phenology, with use of a method that accounts for phylogenetic relationships among species. If nutritional and structural fruit traits are generally lineage-specific, a cross-species comparison of these traits in relation to phonology may fail to detect any trends because the lineage-effects confound the effects of phenology.

The Caloric Content of Migrating Birds

Determinations of kilocalories per ash—free gram dry weight of 32 individuals of 20 species ranging from exceedingly fat migrants to lean nonmigrant birds revealed the following: 1) Long—range migrants at peak of fat decomposition in the fall had a caloric content of 7.9 to 8.3 (mean 8.1) kcal/g ash—free dry weight. 2) Spring arrivals were between 5.7 and 7.4 (mean 7.0). 3) Lean nonmigrants were between 6.0 and 6.9 (mean 6.3). 4) The caloric value of the ash—free nonfat body component was the same for all three groups, averaging about 5.5, indicating that decomposition and utilization of fat during migration does not affect the caloric content of the nonfat portion of the bird's body.

Differences between Migrant and Non-Migrant Birds in Food and Water Intake at Various Temperatures and Photoperiods

Differences between Migrant and Non-Migrant Birds in Food and Water Intake at Various Temperatures and Photoperiods