Core farming activities were balanced against additional hunting and foraging tasks across the wider land- and seascapes of southwest Greenland and long expeditions to the northern walrus hunting grounds (McGovern 1985; Enghoff 2003) and communal hunting drives to harvest migrating seals (McGovern et al. 1988). Zooarchaeological analyses have recorded an increased dietary reliance on migratory harp seals in both the Eastern and Western settlements from AD 1300 (Ogilvie et al. 2009; Smiarowski et al. 2017). Other communal hunting and foraging tasks would have taken place on a seasonal basis such as harvesting nesting birds in the spring and caribou hunting in the late autumn (Dugmore et al. 2007a).
The International Union for Conservation of Nature (IUCN) and Bird Life Species has recognized over 20% of approximately 10,000 extant bird species as being threatened. As of 2014, the IUCN RedList has declaredfive, 1,373, and 959 species as extinct in the wild, threatened, and near threatened, respectively. Between 1988 and 2008, the conservation status of 235 species was upgraded to higher categories of endangerment, as compared to just 32 species that were downgraded . Furthermore, historical records document the extinction of at least 150 avian species since the 16th century. The principal threats leading to avian population decline have been linked to man-made environmental disasters, including over-hunting, habitat loss, pesticide abuse, and invasive species introduction . To combat the ongoing decline, conservation efforts have been made, such as protective legislation, habitat restoration, captive breeding, and reintroduction, and all are responsible for the successful recovery of 49 species that were near-extinct between 1994 and 2004 .
Differences in the size and structure of corridor and woodlot habitats could also affect other ecological factors, which could, in turn, influence stress physiology of migrant birds. In southeastern South Dakota, the average size of corridor woodlands is more than three times larger than woodlots, which results in much greater amounts of woodland edge for woodlot habitats, and corridors also harbour more diverse vegetation than woodlots (Castonguay, 1982; Gentry et al., 2006; Liu and Swanson, 2014). These differences in size, structure and vegetative diversity of corridors and woodlots may produce differences in predation pressure, competition among migrants and thermal microclimates (Ellis et al., 2012), all of which could potentially influence stress physiology. Predation pressure can alter the stopover biology of migrants (Lank et al., 2003; Pomeroy, 2006; Taylor et al., 2007) and influence the stress response (Cockrem and Silverin, 2002; Clinchy et al., 2004; Newman et al., 2013). Smaller woodland parcel size and increased edge facilitate the access of predators to smaller woodlands (Donovan et al., 1997; Tewksbury et al., 2006), so predation pressure is expected to be higher in woodlots than in corridors in our study area. Such differences in predation pressure could result in differences in stress physiology between migrants in corridors and woodlots in the present study.
Competition may also influence stress physiology, and better competitors, such as birds with better body condition or of larger size, may show lower CORTB and a greater magnitude of the stress response (Lehnen and Krementz, 2005; Braasch et al., 2014). Hatch-year birds are usually socially subordinate to adults, which may restrict the former's access to limited resources due to competitive interactions with adults (Moore et al., 2003; Faaborg et al., 2010). In addition, because juveniles in autumn are experiencing their first migration, foraging efficiency during stopover may be lower than that of experienced adults (Yong et al., 1998; Heise and Moore, 2003). Consequently, the stress response might differ between ages, with higher CORTB and a lower stress response in juveniles than in adults. The age ratios of migrants at woodlot and corridor study sites differ, with higher proportions of juveniles at woodlot sites, perhaps resulting from competition with adults (Dean et al., 2004; Liu and Swanson, 2014); therefore, differences in stress physiology between birds in corridors and woodlots as a function of differing competitive interactions or differing age ratios might be expected.
Hatch-year migrants are undertaking their first migration in autumn, so they are less experienced foragers than adults, which could result in lower refuelling rates, although age-related differences in body condition and refuelling rates are seldom detected at stopover sites (e.g. Seewagen et al., 2013; Liu and Swanson, 2014). Moreover, juvenile migrants are usually socially subordinate to adults, which may restrict the former's access to limited resources due to competitive interactions with experienced adults (Yong et al., 1998; Heise and Moore, 2003; Moore et al., 2003; Faaborg et al., 2010). As a consequence, the stress response may differ between age classes, with higher CORTB and a lower stress response in juveniles than in adults. In the present study, we did not detect significant differences in CORTB, CORT30 or the magnitude of the stress response between adults and juveniles. This is similar to the results of Thomas (2008), who found little difference in plasma CORT levels between adult and juvenile least (Calidris minutilla) and semipalmated sandpipers (Calidris pusilla). This suggests that ecological and environmental conditions at our stopover sites provided effective stopover habitat for both adults and juvenile birds such that age-related differences in stress physiology were not evident.
The migration modulation hypothesis proposes that migrants maintain elevated CORTB levels during migration and show a suppressed stress response when faced with additional acute stressors (Holberton et al., 1996), thereby facilitating fattening while sparing muscle protein. Consistent with this hypothesis, elevated CORTB levels, a suppressed stress response, or both, occur in a number of wild migrant or photostimulated, migratory-ready captive birds (Holberton et al., 1996, 2007; Piersma et al., 2000; Landys-Ciannelli et al., 2002; Long and Holberton, 2004). However, numerous studies also document significant stress responses in wild migrant or photostimulated captive birds (Romero et al., 1997; Piersma et al., 2000; Landys-Ciannelli et al., 2002; Falsone et al., 2009; Nilsson and Sandell, 2009), suggesting that full suppression of the stress response does not occur in most migrants or that the degree of suppression changes with the stage of migratory stopover. However, the magnitude of the stress response in these birds may sometimes be influenced by body condition (Mizrahi et al., 2001; Jenni-Eiermann et al., 2009; Raja-aho et al., 2010), so energetic condition could influence the modulation of the stress response during migration. A corollary prediction of the migration modulation hypothesis is that CORTB and the magnitude of the stress response should be inversely related, even if the stress response is not fully suppressed. The suppressed stress response when facing additional acute stressors might result from negative feedback of elevated CORTB during migration (Raja-aho et al., 2010). In the present study, we found a significant negative relationship between CORTB and the magnitude of the stress response, despite robust stress responses for all bird groups studied, which is consistent with this corollary prediction of the migration modulation hypothesis.
At present, the most commonly used birds are the passerines (order Passeriformes), and the bird market is mostly domestic . Most wild birds are captured in their natural habitat and a small fraction of them are bred in captivity for their commercialization . In Mexico, the bird traders are called pajareros (derived from pájaro, the Spanish word for bird), and they have maintained the cultural tradition of capturing and maintaining wild birds for sale; this is an activity that, according to historical documents, is of Prehispanic origin [14, 15]. Among the few accounts of the pajarero activity in Mexico, the best reports are by Mellink and collaborators [16,17,18], who described the use of wild birds in the Potosino-Zacatecano Plateau region in north central Mexico. Research on this topic in Latin America is very scarce, and most of the studies consist of birds on the useful bird species list. There are few studies with qualitative data describing the social characteristics of bird users or depicting the interesting capture techniques that they have developed. These studies do not include literature on the extraordinary traditional bird knowledge that these people have. More research regarding this activity has been published for Brazil , despite the fact that birds are used as pets in all Latin American countries (e.g., ).
The pajarero trade is a well-established production chain, beginning with the capture of wild birds, continuing with their acclimation and maintenance, and finishing with their sale (Fig. 3). At the community scale or micro-region, the households and leaders in charge of accumulating the captured birds are linked to the production chain; they are sometimes also involved in the acclimation and maintenance of the birds and, if necessary, in transporting the birds to the localities of wholesaler households, which act at a regional scale. 1e1e36bf2d