Michael D. Kern

Seasonal changes in the reproductive system of the female white-crowned sparrow, Zonotrichia leucophrys gambelii, in captivity and in the field. 2. The incubation patch.

SummaryThe ventral apterium of free-living female White-crowned Sparrows (Zonotrichia leucophrys gambelii) becomes an incubation patch during the breeding season. At this time, it loses its feathers, increases in wet and defatted dry weight, and undergoes marked histological alterations. At times of year other than the breeding season, the apterium consists of a low squamous epidermis and a thin, poorly vascularized dermis of dense connective tissue. The dermis is separated from subcutaneous tissue by an internal elastic lamina. During the breeding season, the epidermis is a proliferative, stratified squamous eptihelium with well-defined basal, intermediate, transitional, and cornified layers; and the dermis consists of a superficial layer of collagen and a deep layer of highly vascular areolar connective tissue, noticeably edematous and mildly inflamed. Blood vessels are frequently in large groups in the center of the dermis. Edema and hypervascularity are most pronounced during incubation, but the epidermis is best developed during egg-laying. The apterium reverts to its basal state after the incubation period. Captive females, which do not breed, do not develop incubation patches.Estrogen is apparently responsible for feather loss and collagen synthesis. It and other unidentified hormones (probably prolactin and/or androgens) produce the hypervascularity, edema, and epidermal growth.

HABITAT AND SEX DIFFERENCES IN PHYSIOLOGICAL CONDITION OF BREEDING SOUTHWESTERN WILLOW FLYCATCHERS (EMPIDONAX TRAILLII EXTIMUS)

Abstract The Southwestern Willow Flycatcher (Empidonax traillii extimus; here- after “flycatcher”) is a federally listed endangered species that breeds in densely vegetated riparian habitats dominated by native and exotic plants, including introduced monotypic saltcedar (Tamarix ramosissima). Some workers have theorized that saltcedar is unsuitable habitat for the flycatcher, primarily because it generally supports a smaller and less diverse invertebrate community (the flycatchers food base) than native habitats (e.g. Salix spp.). However, differences in insect communities between native and saltcedar habitats are not proof that saltcedar habitats are inferior. The only way to evaluate whether the habitats differ in dietary or energetic quality is to document actual food limitation or its manifestations. Measurements of an individuals body condition and metabolic state can serve as indicators of environmental stressors, such as food limitation and environmental extremes. We captured 130 flycatchers breeding in native and saltcedar habitats in Arizona and New Mexico and measured 12 variables of physiological condition. These variables included body mass, fat level, body condition index, hematocrit, plasma triglycerides, plasma free fatty acids and glycerol, plasma glucose and beta-hydroxybutyrate, plasma uric acid, total leukocyte count, and heterophil-to-lymphocyte ratio. We found substantial sex-based differences in the condition of male and female flycatchers. Ten of the 12 measures of physiological condition differed significantly between the sexes. In all cases where male and female condition differed (except mass), the differences suggest that males were in poorer condition than females. We found few habitat-based differences in flycatcher condition. Only 3 of the 12 physiological condition indices differed significantly between habitats. Our data show that, at least in some parts of the flycatchers range, there is no evidence that flycatchers breeding in saltcedar habitats exhibit poorer nutritional condition or are suffering negative physiological affects. Diferencias entre Hábitats y Sexos en la Condición Fisiológica de Individuos Reproductivos en Empidonax traillii extimus

Racial Differences in Nests of White-Crowned Sparrows

Comparaison des nids de Zonotrichia leucophrys leucophrys, du Manitoba, Z.l. oriantha de Californie et du Colorado et Z.l. nuttalli de Californie. Les nids varient par la taille, leur elevation, leur conductance thermique

Possible roles for corticosterone and critical size in the fledging of nestling pied flycatchers

Our study was designed to see whether corticosterone (B) rises abruptly in the blood of nestling pied flycatchers (Ficedula hypoleuca) at the time they fledge, as reported recently for kestrels, and if so, why. We measured the growth and blood levels of B and selected nutrients of nestlings in broods of five, seven, and nine chicks during 1998 and 1999. In half of the broods, we clipped selected wing and tail feathers of both parents with the intention of making it more difficult for them to provide their chicks with food. We collected blood samples when the chicks were six to 10 d old (period of rapid growth) and 15 d of age or older (0–5 d before fledging). B increased substantially several days before the chicks left the nest and then declined somewhat. We found no differences in rates of growth or blood levels of B, nutrients, and hematocrit as a function of either brood size or parental handicapping. Nestlings within a day of fledging appear to have been food deprived in 1998; their glucose was significantly reduced, and B, free fatty acids, and glycerol were significantly elevated compared to levels in chicks 1–4 d younger. Such changes did not occur in 1999. Blood levels of B were significantly correlated with brood size near the day of fledging, but not earlier, in both years of the study. It was possible to predict the day on which chicks would leave the nest, using their wing length when 12 d old. These results suggest that high blood levels of B associated with food restriction and sibling competition induce chicks to fledge, provided they have reached a critical size, and that the importance of fasting, sibling competition, and B may vary from year to year.

GAS PERMEABILITY OF AMERICAN ALLIGATOR EGGS AND ITS ANATOMICAL BASIS

The barrier to gas flux across the eggs of American alligators (Alligator mississippiensis) consists of a calcareous shell and an underlying shell membrane of two layers, a limiting membrane facing the embryo and a fibrous membrane facing the shell. The limiting membrane is penetrated by an immense population (averaging 341,188 cmT2) of tiny pores (averaging 0.51 mm in diameter) and a small population (averaging 190 cm−2) of large pores (averaging 34.6 mm in diameter). An estimated 6% of these pores are open at the onset of incubation, and 22%‐24% are open near hatch. The shell membrane is 2.6–10 times less permeable to O2 than the shell. Its permeability nearly quadruples during incubation, is higher at the equator than elsewhere, increases more rapidly when eggs are incubated at 33°C as opposed to 30°C, and appears to depend primarily on its water content. In contrast, the shells permeability to O2, as well as its water vapor conductance and the number of open pores in it, does not change significantly during incubation.

Water Loss, Conductance, and Structure of Eggs of Pied Flycatchers during Egg Laying and Incubation

Eggs of Pied Flycatchers (Ficedula hypoleuca) lose water at a slow, constant rate (

Environmentally relevant bouts of cooling stimulate corticosterone secretion in free-living eastern bluebird (Sialia sialis) nestlings: Potential links between maternal behavior and corticosterone exposure in offspring

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Changes in water-vapor conductance of common canary eggs during the incubation period

) during egg laying but at a much higher, linear rate during incubation. Prepipping losses average 20% of the eggs mass when freshly laid. The watervapor conductance (