Dispersal of introduced house sparrows Passer domesticus: an experiment

An important issue concerning the introduction of non-indigenous organisms into local populations is the potential of the introduced individuals to spread and interfere both demographically and genetically with the local population. Accordingly, the potential of spatial dispersal among introduced individuals compared with local individuals is a key parameter to understand the spatial and temporal dynamics of populations after an introduction event. In addition, if the variance in dispersal rate and distance is linked to individual characteristics, this may further affect the population dynamics. We conducted a large-scale experiment where we introduced 123 house sparrows from a distant population into 18 local populations without changing population density or sex ratio. Introduced individuals dispersed more frequently and over longer distances than residents. Furthermore, females had higher probability of dispersal than males. In females, there was also a positive relationship between the wing length and the probability of dispersal and dispersal distance. These results suggest that the distribution and frequency of introduced individuals may be predicted by their sex ratio as well as their phenotypic characteristics.     

Circadian entrainment by feeding cycles in house sparrows,Passer domesticus

Summary We studied the potential zeitgeber qualities of periodic food availability on the circadian rhythms of locomotor and feeding activity of house sparrows. The birds were initially held in a LD-cycle of 12:12 h, with food restricted to the light phase. After transfer to constant dim light, the birds remained entrained by the restricted feeding schedule. Following an exposure to food ad libitum conditions, the rhythms could be re-synchronized by the feeding cycle. Shortening of the zeitgeber period to 23.5 h resulted in the loss of entrainment in most birds, whereas a longer zeitgeber period of 25 h re-entrained the rhythms of most birds. Although these results prove that periodic food availability can act as a zeitgeber for the circadian rhythms of house sparrows, several features of our data indicate that restricted feeding is only a weak zeitgeber. The pattern of feeding activity prior to the daily time of food access shown under some experimental conditions suggests that anticipation is due to a positive phase-angle difference of the birds' normal circadian system rather than being caused by a separate pacemaker.     

A taste for novelty in invading house sparrows, Passer domesticus

One of the central questions in invasion biology involves whysome introductions succeed and others fail. Although severalcorrelates of invasion success have been identified, patternsalone cannot identify the mechanisms underlying the invasionprocess. Here, we test the hypothesis that one predictor ofinvasion success, behavioral flexibility, is different betweeninvading and established populations of the same species ofbird. We predicted that neophobia (fear of novelty), a surrogateof behavioral flexibility, would be weaker in an actively invadingpopulation (28 years resident; Colon, Republic of Panama) ofhouse sparrows (Passer domesticus) compared to a populationthat had been resident for more than 150 years (Princeton, NewJersey, USA). To test this hypothesis, we compared latency toconsume novel foods and phobia of novel objects between populationswhen both were kept under similar environmental conditions incaptivity. As predicted, birds from the 150-year-old populationtook significantly longer to approach and consume novel foodsthan birds from the 28-year-old population. Responses to novelobjects were not different between populations however; bothpopulations fed more readily near some novel objects, whichto our knowledge is the first such occurrence in a wild vertebratespecies. Overall, a predilection for trying new foods and beingattracted to novel objects may in part explain how this specieshas so successfully invaded new areas.     

Experimental test of a trade‐off between moult and immune response in house sparrows Passer domesticus

A trade‐off between immune system and moulting is predicted in birds, given that both functions compete for resources. However, it is unclear whether such a trade‐off exists during post‐breeding moult. This study tests such a trade‐off in the house sparrow (Passer domesticus). Males injected with an antigen (lipopolysaccharide) significantly moulted slower than sham‐injected males. Moreover, males whose seventh primaries were plucked to simulate moult showed smaller immune response to phytohaemagglutinin than control males, in which seventh primaries were clipped. A trade‐off between moult speed and body mass was also found. The results show a clear trade‐off between moult and immune response in the house sparrow: immune response negatively affected moult and moult negatively affected immune response. These findings suggest that only individuals in good condition may have an efficient moult and simultaneously respond effectively in terms of immunity to pathogens, which could explain how plumage traits honestly indicate parasite resistance in birds.     

Toxicity of sodium chloride to house sparrows (Passer domesticus)

Sodium chloride (NaCl) is widely used as a deicing agent on roadways. There are numerous anecdotal reports of poisoning of passerine birds by road salt in the United States and Canada, but little is known about the toxicity of NaCl to songbirds. The objectives of this study were to determine the lethal dose range for NaCl in a representative passerine species (house sparrow [Passer domesticus]); to determine the clinical, physiologic, and pathologic effects of sublethal and lethal oral NaCl exposure; and to assess the potential for recovery after exposure to granular salt or highly concentrated salt solutions. The up-and-down method was used in a pilot study to estimate the lethal oral dose of granular NaCl in wild caught house sparrows. The toxicity of highly concentrated NaCl solution also was investigated. This was followed by an acute dose response study in which house sparrows were dosed orally with granular NaCl at 0, 500, 1,500, 2,500, or 3,500 mg/kg. Sparrows were deprived of water for 6 hr postexposure (PE) in an attempt to mimic specific winter conditions. Groups of three birds at each dose were euthanized at 1, 3, 6, and 12 hr PE, and samples were collected for histopathology and brain and plasma electrolyte analyses. Results indicated an approximate mean lethal dose (LD50) of 3,000-3,500 mg/kg in water-deprived birds, which is similar to mammalian values. House sparrows dosed with a concentrated solution of NaCl generally died at doses of 8,000 mg/kg. Clinical signs observed at >or=1,500 mg/kg included rapid onset (<30 min) of depression (indicated by reduced activity and reduced response to visual and auditory stimuli), ataxia, inability to fly or perch, and death in as little as 45 min. Birds that survived for 6 hr usually recovered. Plasma Na concentrations >200 mmol/l were consistently associated with clinical signs. Pathologic lesions consisted of edema and distension of the caudoventral thin muscled region of the gizzard and were observed 1 hr PE in most birds dosed with >or=500 mg/kg. Brain Na concentrations in clinically ill sparrows and those that died of NaCl toxicity ranged from 1,297 to 1,615 (mean=1,450; SD=115) ppm wet weight or 5,603 to 6,958 (mean=6,367; SD=454) ppm dry weight, which differed significantly from control birds. No histologic lesions were observed in brain sections of exposed birds, likely reflecting the acute nature of the exposure. However, fluid accumulation beneath the koilin layer of the gizzard was observed in the majority of birds at high dosage levels. These results indicate that passerines ingesting relatively small numbers of road salt granules or small quantities of highly concentrated NaCl solutions are at risk of sodium poisoning.     

Age-related patterns of reproductive success in house sparrows Passer domesticus

A common life history pattern in many organisms is that reproductive success increases with age. We report a similar pattern in house sparrows Passer domesticus , older individuals performed better than yearlings for most measures of reproductive success. Older males and females began breeding earlier in a given season and fledged more young than their yearling counterparts. Individual males also fledged more young in their second breeding season than they did in their first, but individual females did not show consistent improvement in reproductive success from year one to two. A path analysis indicated that age in both sexes acted primarily through the timing of breeding; earlier nesters laid more eggs and hence fledged more young but did not have more nesting attempts. We tested whether the increased reproductive success with age arose from high quality individuals surviving to be older (selection hypothesis). In contrast to the main prediction of this hypothesis that reproductive success and survival should be positively related, we found that survival from one year of age to two years of age was negatively related to reproductive success in the first year for males and females combined. Additionally, individuals that survived to breed as two-year-olds did not differ in total young fledged in their first year from those that did not survive to their second season of breeding. Our results indicate that fledgling production increases with age due to improvements in timing of breeding, particularly in females, and not because of the loss of poor breeders or increased output. Mechanisms producing age-related differences in timing of breeding warrant further study.     

Developmental changes in digestive physiology of nestling house sparrows, Passer domesticus

Six decades of studies have speculated that digestive capacity might limit avian growth rate or that developmental changes in the gut might determine developmental changes in digestive efficiency. However, there are no studies on digestive enzymes during avian development, except for studies on mainly domestic birds that exhibit the precocial mode of development. We studied alimentary organ masses, intestinal enzyme activities (sucrase, maltase, isomaltase, aminopeptidase-N), and pancreatic enzyme activities (amylase, trypsin, chymotrypsin) during development of a wild passerine bird exhibiting the altricial mode of development. Wild nestling house sparrows were studied immediately after removal from the nest (days 0, 3, 6 of age; day 0=hatch), whereas captives were raised in the laboratory beginning day 3 on a formulated casein/starch-based diet until fledging age (after day 12). Digestive biochemistry was dynamic. Tissue-specific activities of some digestive enzymes continued to increase through fledging, by >10 times in some cases (e.g., sucrase and maltase in midintestine). Total pancreatic amylase activity increased 100 times between hatch and day 12 through a combination of increases in tissue-specific activity and pancreas mass. House sparrows differ from poultry, in whom after about 2 wk of age the specific activity of intestinal and pancreatic digestive enzymes is generally constant or declines during development. The data on intestinal and pancreatic enzymes help explain why digestive efficiency of nestling house sparrows improves with age, and the data seem consistent with the idea that digestive capacity might limit feeding rate and hence growth rate.     

Cutaneous immune activity varies with physiological state in female house sparrows (Passer domesticus)

Many vertebrates show seasonality in immune defenses, perhaps because of trade-offs with other physiological processes. Trade-offs between reproduction and immune function have been well studied, but how other life cycle events such as molt affect immune function remains unclear. Here, we hypothesize that one possible explanation is that accumulative dissociated processes (e.g., resource deficits generated over the long term by physiological processes) can have delayed effects on immune activity. To test this hypothesis, we compared cutaneous immune responses in groups of captive female house sparrows (Passer domesticus) photoperiodically induced into six different life cycle stages. We predicted that if delayed trade-offs occur, immune activity would be reduced after a mature life state was reached (e.g., postmolt) and not just compromised when other tissues were actively growing (instantaneous trade-off). We found evidence for both types of trade-offs: immune responses were weakest in sparrows that had just completed postnuptial molt, but they were also weak in birds growing reproductive tissues or feathers. Birds in mature reproductive states or light molt had strong immune responses comparable with birds in a nonbreeding/nonmolting state. Altogether, our results indicate that immune activity in female house sparrows can be influenced by both instantaneous and delayed trade-offs.     

Contrasting adaptive immune defenses and blood parasite prevalence in closely related Passer sparrows

Immune system components differ in their functions and costs, and immune defense profiles are likely to vary among species with differing ecologies. We compared adaptive immune defenses in two closely related species that have contrasting inflammatory immune responses, the widespread and abundant house sparrow (Passer domesticus) and the less abundant tree sparrow (Passer montanus). We found that the house sparrow, which we have previously shown mounts weaker inflammatory responses, exhibits stronger adaptive immune defenses, including antibody responses, natural antibody titers, and specific T-cell memory, than the tree sparrow. Conversely, tree sparrows, which mount strong inflammatory responses, also mount stronger nonspecific inflammatory T-cell responses but weaker specific adaptive responses. Prevalence of avian malaria parasite infections, which are controlled by adaptive immune defenses, was higher in the geographically restricted tree sparrow than in the ubiquitous house sparrow. Together these data describe distinct immune defense profiles between two closely related species that differ greatly in numbers and distributions. We suggest that these immunological differences could affect fitness in ways that contribute to the contrasting abundances of the two species in North American and Western Europe.     

Constraints on home range behaviour affect nutritional condition in urban house sparrows (Passer domesticus)

In human‐dominated landscapes (semi)natural habitats are typically embedded in tracts of unsuitable habitat. Under such conditions, habitat characteristics and grain size of the surrounding landscape may affect how much food, and at what cost, is available for sedentary species with low home‐range plasticity. Here we combine behavioural radio‐tracking, feather ptilochronology, and landscape analysis to test how nutritional condition varies with home range size in 13 house sparrow [Passer domesticus (Linnaeus, 1758)] populations along an urban gradient. Urban individuals occupied smaller home ranges than conspecifics from rural areas, most distinctly if key cover was highly scattered. In urban plots, patch connectivity, home range sizes, and activity areas were positively correlated, indicating that individual ranging behaviour was related to the spatial distribution of suitable habitat. Urban House sparrows also showed the smallest feather growth bars, which were positively related to home range size at plot level. In contrast, growth bar widths and home range sizes were negatively related in rural populations, whereas in suburban populations, both variables varied independently. We conclude that individuals from progressively more built‐up areas show a restricted ability to adjust their daily ranging behaviour to the scattered distribution of critical resources. This may complement other putative causes of the widespread population decline of urban house sparrows. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 41–50.     

Reproductive state, but not testosterone, reduces immune function in male house sparrows (Passer domesticus)

The immune system requires energetic and nutritional resources to optimally defend organisms against pathogens and parasites. Because resources are typically limited, immune function may require a trade-off with other physiologically demanding activities. Here, we examined whether photoperiodically induced seasonal states (breeding, molting, or nonbreeding) affected the cutaneous immune response of captive male house sparrows (Passer domesticus). To assess immune function in these birds, we injected the mitogen phytohemagglutinin (PHA) into the patagium and measured the resulting wing web swelling. Molting and nonbreeding birds had similar immune responses to PHA injection. However, males in a breeding state showed lower immune responses than both molting and nonbreeding birds even though they did not actually breed. We tested whether this decrease in the PHA swelling response in birds in a breeding state was due to elevated plasma concentrations of testosterone (T) by administering T to birds in a nonbreeding state. Contrary to some evidence in the literature, T did not suppress the response to PHA in house sparrows. Our data show that passerine birds show seasonal modulation in immune function, even in benign environmental conditions. However, even though T is often cited as a strong immunosuppressant, it is not fully responsible for this seasonal modulation.     

Genetic relatedness in wintering groups of house sparrows (Passer domesticus)

Social behaviour of group-living animals is often influenced by the relatedness of individuals, thus understanding the genetic structure of groups is important for the interpretation of costs and benefits of social interactions. In this study, we investigated genetic relatedness in feeding aggregations of free-living house sparrows ( Passer domesticus ) during the nonbreeding season. This species is a frequent model system for studies of social behaviour (e.g. aggression, social foraging), but we lack adequate information on the kin structure of sparrow flocks. During two winters, we ringed and observed sparrows at feeding stations, and used resightings to identify stable flock-members and to calculate association indices between birds. We genotyped the birds using seven highly polymorphic microsatellite loci, and estimated pairwise relatedness coefficients and relatedness categories (close kin vs. unrelated) by maximum likelihood method. We found that most birds were unrelated to each other in the flocks (mean ± SE relatedness coefficient: 0.06 ± 0.002), although most individuals had at least a few close relatives in their home flock (14.3 ± 0.6% of flock-mates). Pairwise association between individuals was not significantly related to their genetic relatedness. Furthermore, there was no difference between within-flock vs. between-flock relatedness, and birds had similar proportions of close kin within and outside their home flock. Finally, relatedness among members of different flocks was unrelated to the distance between their flocks. Thus, sparrow flocks were not characterized by association of relatives, nevertheless the presence of some close kin may provide opportunity for kin-biased behaviours to evolve.     

Metabolic and ventilatory acclimatization to cold stress in house sparrows (Passer domesticus)

Passerines that overwinter in temperate climates undergo seasonal acclimatization that is characterized by metabolic adjustments that may include increased basal metabolic rate (BMR) and cold-induced summit metabolism (M(sum)) in winter relative to summer. Metabolic changes must be supported by equivalent changes in oxygen transport. While much is known about the morphology of the avian respiratory system, little is known about respiratory function under extreme cold stress. We examined seasonal variation in BMR, M(sum), and ventilation in seasonally acclimatized house sparrows from Wisconsin. BMR and M(sum) increased significantly in winter compared with summer. In winter, BMR increased 64%, and M(sum) increased 29% over summer values. The 64% increase in winter BMR is the highest recorded for birds. Metabolic expansibility (M(sum)/BMR) was 9.0 in summer and 6.9 in winter birds. The metabolic expansibility of 9.0 in summer is the highest yet recorded for birds. Ventilatory accommodation under helox cold stress was due to changes in breathing frequency (f), tidal volume, and oxygen extraction efficiency in both seasons. However, the only significant difference between summer and winter ventilation measures in helox cold stress was f. Mean f in helox cold stress for winter birds was 1.23 times summer values.     

Body‐mass‐dependent trade‐off between immune response and uropygial gland size in house sparrows Passer domesticus

Parasites greatly impact host fitness. The immune system is fundamental to combat endoparasites, and survival increases with greater investment in immunity. Some ectoparasites, by contrast, are reportedly combated by the use of the uropygial gland, an organ exclusive to birds, which secretes an oily substance (preen oil) that is spread on plumage. However, both mounting an immune response against a parasite and producing uropygial gland secretion depend on the same resources, a situation which may induce trade‐offs between the two antiparasitic functions. In this study, I experimentally test whether immune response is traded off against uropygial gland size in the house sparrow Passer domesticus. In the experiment, a group of sparrows were injected with an antigen (lipopolysaccharide, LPS), which stimulates the immune system, while the other group received a sham injection. The uropygial gland of LPS‐treated birds decreased significantly more than that of the control birds after treatment. Nevertheless, the effect of the treatment was limited to house sparrows with low body mass, suggesting that heavy house sparrows were able to produce an immune response while maintaining a relatively large uropygial gland. Given that uropygial gland size is strongly related to production of preen oil, these results suggest that preen oil production declines in birds in poor body condition when resources are preferentially diverted to other demanding functions, such as the immune system. Considering that the uropygial gland is involved in several fitness‐related processes in birds, the trade‐off between immune response and uropygial gland size may have important consequences for bird life histories.     

The mask of seniority? A neglected age indicator in house sparrows Passer domesticus

In many species, females prefer older males as social and genetic mates, and male secondary sexual traits often act as age indictor mechanisms. It has been reported that almost all the extra-pair paternity in one population and recently in another population of house sparrows Passer domesticus , was achieved by males more than one year old. We aimed to determine whether there is a morphological trait that distinguishes yearlings from older males in house sparrows. Here, we report that such a trait – the extent of black around a male's eye, which we term the 'mask' or 'mask of seniority', is a reasonable indicator of male age, being adequate to assign yearlings and older males correctly 81% of the time. It is well known that a male's black throat patch, often called the 'badge' or 'badge of status', signals fighting ability. We speculate that badge size signals dominance, and is therefore often used in male–male competition, whereas mask size may play a key role as an age indicator mechanism, potentially used in female choice. It is surprising that this important trait evaded researchers' attention during 20 years of house sparrows being a model organism for sexual selection.     

Renal response to dietary protein in the house sparrow Passer domesticus

Many birds switch seasonally or during ontogeny between diets of varying protein content. In mammals, high-protein diets induce hypertrophy of the kidney in general and of the thick ascending limbs (TAL) in particular, along with increases in glomerular filtration rate (GFR) and urine flow. A hypothesis to explain these phenomena is that the TAL become increasingly sensitive to peptide hormones (glucagon and antidiuretic hormone [ADH]) released in response to protein feeding; the consequent enhancement of ion reabsorption dilutes urine reaching the macula densa, thereby suppressing tubulo-glomerular feedback (TGF) and causing a rise in GFR. Avian kidneys possess most of the elements involved in this mechanism, including loops of Henle with TAL, sensitivity of TAL to ADH (arginine vasotocin [AVT] in birds), and the elements of TGF. We therefore hypothesized that switching from a low-protein to a high-protein diet would induce responses in birds similar to those found in mammals. We tested this hypothesis by feeding house sparrows, Passer domesticus, isocaloric diets containing either 8% or 30% protein. Birds on high-protein food had larger renal medullae, both in mass and in TAL diameter, but no increase in whole-kidney mass. Urine flow was approximately doubled on high-protein food, but there was no change in GFR. We were not able to detect an increased sensitivity of AVT-induced adenylyl cyclase activity in TAL from high-protein animals, and responsiveness to glucagon was higher in TAL from birds eating low-protein food. We are unable to conclude that a suppression of TGF is responsible for the rise in urine flow in birds eating high-protein foods, and the mechanisms behind the medullary hypertrophy and the diuresis remain to be fully explored.     

Reduced parental effort in relation to laying date in house sparrows (Passer domesticus): a study under controlled conditions

It is known that breeding success in birds declines with an advance in the laying date. In this paper, breeding success diminished with laying date in a house sparrow (Passer domesticus) population breeding in captivity. The principal cause of the cline in breeding success with date was a decrease in the female feeding rate. The parental effort in females decreased with the advance of the laying date, although food access was ad libitum throughout the breeding season. Consequently, this cline in breeding success may be due to a reduced parental investment with the advance of the laying date or to exhaustion due to previous reproductive events in the season. Hypotheses usually used to explain the cline in breeding success with date can not explain results in this study.