Tarsus Growth Research Articles

Habitat-Specific Growth and Fitness in Carrion Crows (Corvus corone corone)

SUMMARY (1) The relationship between habitat, chick growth, fledging size and fitness of breeders was studied in two populations of carrion crows, Corvus corone corone L., one living in an urban and another in an agricultural environment in south-western Switzerland. The logistic equation was used to model weight gain and tarsus growth, and the growth constant (k) and the asymptote (a) computed, using an iterative least square fitting technique. The chicks in the two habitats are compared with respect to the parameters a and k of the logistic equation. The Darwinian fitness is evaluated for each habitat. (2) Chicks in the urban habitat gain weight slower, take longer to reach fledging weight and are significantly lighter at fledging than the chicks in the agricultural habitat. Thus, for the weight curves, the chicks in the urban habitat show significantly lower values for both parameters a and k. (3) Tarsus growth is slower for chicks in the urban habitat, but in contrast to weight gain, growth of tarsus is not prolonged. For tarsus growth the parameter k is identical in the two habitats, but urban chicks show significantly lower values for the parameter a. Tarsus length is fixed by the age of fledging. Chicks in the urban habitat have shorter tarsi at fledging. (4) Growth of wing is slower in the urban habitat, but, since wing length is incomplete at fledging, no curves were fitted. (5) Tarsus length of territory-holding adults was measured in both habitats and a critical minimum size for territory acquisition empirically established. Of all fledglings raised in the urban habitat, 79% fall below this critical size and will therefore be unable to acquire a territory and thus be excluded from breeding, whereas only 24% of fledglings raised in the agricultural habitat will be excluded. (6) Successful parents in the agricultural habitat fledge, on average, 2-7 chicks per year, parents in the urban habitat 1 5 chicks only. 36% of all territory holders in the agricultural habitat fledge young, 39% in the urban habitat. Since a much higher percentage of fledged chicks reach the critical body size in the agricultural habitat, these parents reach a Darwinian fitness five times higher than the parents in the urban habitat.

Paternal influence on growth and survival of dark-eyed junco young: do parental males benefit?

Recent studies of typically monogamous passerine birds have suggested that the fitness benefits males derive by caring for their young may not be as great as was previously thought. This study was conducted to determine whether parental care by male dark-eyed juncos, Junco hyemalis, serves to increase either the quantity or quality of young that they produce. Over a 4-year period, males were caught at the time their eggs hatched, and the subsequent growth and survival of the young of unaided females and control pairs were compared. Broods raised by unaided females gained body mass more slowly and fledged at slightly lower mass than those raised by two parents. However, fledging mass was not correlated with survival to independence. There were no differences in tarsus growth between the two treatment groups. Entire brood loss to predators occurred as often among females without male help as it did among those with male help. However, partial brood loss was more common among female-only broods than among controls; this difference was largely attributable to higher rates of starvation and exposure in female-only broods. There appeared to be an interaction between growth and predation. Female-only broods that were below the median mass of combined treatment groups at 5 days of age were more likely than all other broods to experience partial or complete predation. Male impact on offspring survival varied with age of the offspring. When years were combined, males tended to increase survival during the first half of the nestling period, but their impact at the time of nest-leaving was minimal. In all years, from nest-leaving to independence (ca. 2 weeks), broods without male help survived only about half as well as did those with male help. Independent young raised by one parent were as likely to return the following spring as were young raised by two parents. Thus, paternal care benefits males by improving the survivorship of their fledglings, and may also act as a buffer against poor female parental quality and inclement weather. However, the magnitude of these benefits is such that bigamous males might achieve greater reproductive success than monogamous males. Various possible male strategies are discussed.

Weathered crude oil effects on chicks of Fork-Tailed Storm-Petrels (Oceanodroma furcata)

Adult Storm-Petrels had between 0.004 and 0.0008 ml of fossil fuel hydrocarbons present in their food samples when they were considered contaminated. Chicks of Fork-Tailed Storm-Petrels (Oceanodroma furcata) were fed 0.1 ml of weathered Prudhoe Bay crude oil, which should be close to the maximum dose they might receive at a feeding. Chicks dosed orally once, twice, or weekly with 0.1 ml weathered Prudhoe Bay crude oil did not differ significantly in gross morphology, bill, tarsus, or wing growth from control chicks. Chicks dosed one time gained weight between the ages of 0–21 days at significantly slower rates. Chicks aged 22–51 days grew similarly regardless of treatment. Dosed chicks fledged on average two days later than control chicks. Ingesting small amounts of weathered oil had little effect perhaps because Storm-Petrels may be able to ingest long-chained hydrocarbons (like petroleum) with relative impunity, because these compounds are relatively nontoxic and are part of their normal diet.

Ecological Aspects of the Reproductive Biology of Eastern Kingbirds: Geographic Comparisons

A geographic comparison of the ecology of Eastern Kingbirds (Tyrannus tyrannus) breeding in New York (NY), and Kansas (KS), USA, was conducted in 1979 and 1980, respectively Emphasis was placed on relating variation in reproductive parameters, both within and between sites, to season and weather. Superimposed on the geographic comparison was a severe drought in KS in 1980. In both populations egg laying peaked at the end of the 1st wk of June, and modal clutch size was three. seasonal declines in clutch size were also nearly identical. Clutch size differences were not significant. Eggs were significantly larger in NY than in KS. The difference was not related to either adult size or annual variation in weather. Egg mass was only weakly correlated with environmental variables (date and temperature), but interruptions in laying followed days of below—average temperatures. Egg mass increased With the order of laying in NY, but decreased in KS. This apparently reflected the stressful conditions for laying females in KS. Incubation was significantly shorter in KS, probably due to warmer air temperatures since an inverse relationship was found between air temperature and incubation length in NY. Smaller egg size in KS may also have contributed to the shorter incubation period. Nestling growth was relatively slow, and despite large mass differences (eggs were heavier in NY) growth rates were nearly identical. Absolute tarsus growth was also significantly greater in NY, but development of the ninth primary was significantly greater in KS. Nestling period length was inversely correlated with primary length in both populations. Emphasis on primary development in KS, where nest success was lower, vs. mass gain in NY, where starvation was more frequent, discussed in terms of tradeoffs to balance losses to predators (KS) and starvation (NY). Growth was negatively correlated with brood size in both populations, but in KS also with date, i.e., seasonal changes probably related to the drought. Productivity was greater in NY, but in neither population did it exceed 1.5 fledglings per nesting attempt. Mortality of fledglings is near zero in both populations due to intense postfledging parental care. Weather has important influences on the breeding biology of kingbirds, yet geographic variation in most traits was small. Hence, kingbird reproduction is not highly adapted to differences in average weather conditions between the sites. Occasional periods of severe weather probably preclude narrow specialization to local conditions. Kingbirds are therefore best characterized as a bet—hedging species. Patterns of growth and reproduction match hypothetical and independently derived predictions based on other aerial insectivores, thus providing support for several recent predictions for life history evolution.