Colleen A. Barber

The high frequency of extra-pair paternity in tree swallows is not an artifact of nestboxes

Abstract A common criticism of nestbox studies is one of creating artificial nesting conditions and breeding behavior different from what would be seen under natural conditions. We assessed the frequency of extra-pair paternity (percentage of broods with at least one extra-pair young) in 25 families of tree swallows (Tachycineta bicolor) nesting in natural cavities and compared it to that in a nestbox population. We found that 84% of females nesting in natural cavities obtained fertilizations from extra-pair males. These extra-pair males fathered 69% of all nestlings. Studies of tree swallows breeding in nestboxes have shown that 50–87% of broods contained extra-pair young, with extra-pair males fathering 38–53% of all the young. In broods with extra-pair paternity, natural cavities contained a significantly greater proportion of extra-pair young than did nestboxes. Despite differences in nesting habitat and female age structure, the frequency of extra-pair paternity did not differ significantly between the natural-cavity and nestbox populations. Therefore, the presence of extra-pair paternity in tree swallows is not an artifact of nestboxes or of artificial nesting conditions.

Varsity athletes have lower 2D:4D ratios than other university students

Abstract The second to fourth digit ratio (2D:4D) is a sexually dimorphic trait with lower finger ratios considered more masculine. These digit ratios are believed to reflect the prenatal hormonal environment with higher exposure to androgens in utero leading to more masculine digit ratios. The 2D:4D ratio has been negatively correlated with many factors, including aggression, physical fitness, and athleticism. We compared 2D:4D finger ratios of (1) male and female varsity athletes (n = 99) versus male and female student non-athletes (n = 122), and (2) males (n = 104) versus females (n = 117). Our results confirmed that both male (mean ± sx : 0.97 ± 0.004) and female (0.98 ± 0.005) varsity athletes had significantly lower ratios than their non-varsity peers (males: 0.99 ± 0.004; females: 1.00 ± 0.006), and that male athletes had significantly lower 2D:4D ratios than female athletes. Overall, males had significantly lower 2D:4D ratios than females (0.98 ± 0.003 vs. 0.99 ± 0.004). A smaller 2D:4D ratio appears to be consistent with participation in varsity sports among both males and females.

Clutch-size manipulations in the Yellow-Headed Blackbird: a test of the individual optimization hypothesis

To test the critical short-term predictions of the individual optimization hypothesis (IOH), Yellow-headed Blackbird (Xanthocephalus xanthocephalus) clutches of three and four eggs were experimentally enlarged or reduced by one egg, and broods were monitored until fledging. Predictions that control clutches would a) have greater fledging success than experimental clutches, and b) produce heavier or bigger offspring than enlarged broods were generally not supported. Within control clutches, the number of nestlings that fledged did not increase with clutch size. In fact, three-egg clutches were more productive than the most common clutch size of four eggs. The IOH appears to be unsupported for this population, at least up until the time of fledging. We suggest a potential insurance value exists for the fourth-laid egg, thus explaining the maintenance of a modal clutch size of four eggs in this species

EXPERIMENTAL MATE REPLACEMENT DOES NOT INCREASE EXTRA-PAIR PATERNITY IN TREE SWALLOWS

Before the onset of female fertility, we removed 12 early–settling male tree swallows (Tachycineta bicolor) from their nest–boxes and mates, and allowed replacement males which had been floaters to settle with the original female residents. We predicted that females which had their original mate choice altered (experimentals) would be more likely to obtain extra–pair fertilizations than females which remained paired with their original, early–settling mates (controls). The proportion of females obtaining extra–pair fertilizations, however, did not differ between controls and experimentals, indicating that mating tactics of female tree swallows were unaffected by mate replacement. However, differences between early–settling and replacement males did exist. Replacement males had shorter wing chords than early–settling males, suggesting that they were younger. Moreover, a significantly greater proportion of replacement males than early–settling males were unringed and thus new to the study site. Our results suggest that if females are choosing males for good genes, then early–settling males are not superior in genetic quality to the smaller replacement males which had originally been floaters.

Paired Male Song Sparrows Sing More When Their Mate is Incubating

Abstract The fertility announcement hypothesis proposes that avian males should sing at a high rate when their mate is fertile to guard their paternity. We examined if male Song Sparrows (Melospiza melodia) sing more during the incubation period when they are free of constraints of physical mate guarding. We assessed song rates of eight males for 1 hr-periods every 1–2 days during each breeding stage over two consecutive broods within one season. Males sang significantly more during periods when their mate was incubating than during the pre-fertile, or fertile periods, or while feeding young (second brood). Males may be singing at high rates during incubation to maintain contact with their mate and/or to advertise for extra-pair copulations.

Parental Provisioning in Melospiza melodia (Song Sparrows)

Abstract We investigated the division of parental care to nestlings in Melospiza melodia melodia (an eastern subspecies of Song Sparrow) by examining parental provisioning rates (number of trips/nestling/h) over two consecutive broods. Song Sparrows are a territorial, socially monogamous passerine with pairs raising up to three broods together over the breeding season. We obtained provisioning rate data for nine pairs over a total of 12 broods (7 first broods, 5 second broods) on at least some of days (stages) 2–3, 5–6, and 8–9 of the nestling period. Of these, we obtained provisioning data over all three nestling stages for six different pairs (five first broods, one second brood). Males and females provisioned young at similar rates throughout the nestling period. Provisioning rates did not differ significantly between first and second broods, but increased significantly as the nestlings aged, reflecting the increased offspring feeding demands. Offspring provisioning does appear to be truly biparental in this eastern subspecies of Song Sparrow.

MALE EUROPEAN STARLINGS DO NOT USE EGG SPOTS AS A CUE TO ADJUST INVESTMENT IN NESTLINGS

Abstract The effects of post-laying egg spottiness on nestling condition and parental provisioning were investigated in a nest box-breeding population of European Starlings (Sturnus vulgaris). Our objectives were to ascertain whether egg spottiness was associated with the nest ectoparasite Carnus hemapterus, and to examine potential relationships between egg spottiness, presence of C. hemapterus, nestling condition, and parental provisioning effort in European Starlings. Spotted-egg clutches were present over all 3 years in our population, but the spots did not reflect C. hemapterus abundance. Nestlings from spotted-egg clutches did not have more C. hemapterus than those from unspotted-egg clutches. However, nestlings from spotted clutches were in better condition than those from unspotted clutches. Nestling condition was not associated with C. hemapterus abundance. Adult male and female provisioning rates to the offspring did not differ between spotted and unspotted clutches. Similarly, the proportion of provisioning visits by males did not differ significantly between spotted and unspotted clutches, indicating that parents in our population of European Starlings do not use egg spots as a cue to altering their provisioning effort. Further research is required to fully understand the cause and consequences of egg spots in European Starlings.

Hematocrit Does Not Indicate Condition in Nestling or Adult European Starlings

Abstract Hematocrit, the percentage of packed red blood cells in blood, has been used as a measure of avian condition. We investigated the relationship between hematocrit and condition in a wild, breeding population of adult European Starlings (Sturnus vulgaris), and their nestlings (at 5- and 11-days post hatch). Hematocrit was not correlated with condition in adults or nestlings at either 5- or 11-days post-hatch. Adult males and females had similar hematocrit values. Hematocrit increased with age; adults had significantly higher hematocrit than both 5- and 11-day old nestlings, and 11-day old nestlings had significantly higher hematocrit than when they were 5 days of age. Hematocrit was not correlated with sampling date, ambient temperature, or relative humidity level, but was positively correlated with sampling time in the day for nestlings (but not adults). Our findings caution against using hematocrit as a measure of condition in birds.

Length of hackle iridescence increases with age in European Starlings (Sturnus vulgaris)

ABSTRACT Bird ornaments, such as plumage and song, can reflect the age of individuals. Knowledge of an individuals age and potential past breeding experience is important to future mates and to scientists studying mate-choice decisions, levels of parental investment, and reproductive performance. The iridescent length of hackles (throat feathers) has been used to sex and age adult European Starlings (Sturnus vulgaris). We confirmed that males have longer portions of hackle iridescence and overall longer hackles than females. Although After Second Year (ASY) adults have longer hackle iridescence than Second Year (SY) adults, only two other studies that we know of have examined the iridescent length of hackles in the same individuals over time. We measured hackle iridescent length of returning adults over 8 years, and discovered that it continues to increase with age in both females (25/26) and males (21/21). It had the greatest increase over the 1-year period when breeding adults switched from the SY to the ASY age category. Total hackle length also continued to increase with age, albeit more reliably for males (18/21) than females (13/26). These results demonstrate that hackle iridescence is a potential signal of age throughout the lifespan of a European Starling.

Do parents listen to their children? : begging does not go unanswered in European starlings (Sturnus vulgaris)

ABSTRACT Begging by nestling passerines is an important way to communicate their state of hunger to parents. We examined whether experimentally increased nestling begging vocalizations can quickly alter parental provisioning rates in European Starlings (Sturnus vulgaris). We predicted that an increase in begging volume heard by parents during the experimental treatment would result in a significantly higher number of provisioning visits compared to the pre-playback control of natural begging levels. Total number of parental provisioning visits during 1 h control and experimental trials were compared for 23 broods of 14-day-old nestlings. Begging calls of each brood were recorded when nestlings were 13 days old; the loudest calls from each brood were made into a 3 min loop and projected continuously the next day during the experimental trial. As predicted, parents provisioned at a significantly higher rate during the experimental trials than the control trials. European starlings are sensitive to begging calls made by their offspring and respond quickly to any changes in their begging vocalizations.