James A. Cox

INFLUENCE OF PRESCRIBED FIRE ON WINTER ABUNDANCE OF BACHMAN'S SPARROW

Abstract Prescribed fire is used extensively to manage breeding habitat for Bachmans Sparrow (Aimophila aestivalis), but little is known about the effects of prescribed fire on winter habitat requirements. We used conspecific recordings in conjunction with point counts to assess relationships between winter sparrow abundance and use of prescribed fire. Counts of sparrows conducted over three winters were higher (0.59 ± 0.42) (x̄ ± SD) when surrounding vegetation was burned the previous breeding season than in areas burned >18 months earlier (0.27 ± 0.38). Year-to-year abundance estimates for individual stations increased an average of 0.39 (± 0.54) individuals per count when surrounding vegetation was burned the previous breeding season and decreased 0.22 (± 0.59) individuals per count when vegetation was not burned. Sparrow counts were positively correlated with percent bare ground cover surrounding census stations and negatively correlated with increases in percent grass cover, grass standing crop, height of grass, and shrubs <1 m in height. Prescribed fire may improve winter foraging conditions for this ground-dwelling species by reducing dense grass cover at ground level. Increased flowering responses that many dominant plants exhibit following burns also may improve winter food resources. We observed color-marked birds (n = 18) in the same areas used during the breeding season and confirmed the maintenance of year-round home ranges by some individuals.

Nest-Site Characteristics of Bachman's Sparrows and Their Relationship To Plant Succession Following Prescribed Burns

Abstract Prescribed fire is a frequently applied land-management tool for the preservation and maintenance of southern pine woodlands. Many avian species benefit from the use of prescribed fire in pine woodlands; however, the effect fire has on nesting site characteristics is not well understood for many disturbance-dependent species. We located nests of Bachmans Sparrows (Peucaea aestivalis) in mature longleaf pine (Pinus palustris) forests managed using frequent prescribed fires (return intervals ≤2 years). Vegetation characteristics were measured at each nest (n  =  37), within a 0.04-ha area immediately adjacent to nests, and at different time intervals following burns within a larger 20-ha area surrounding nests. We examined vegetation characteristics within the 20-ha area 2, 6, 12, and 18 months after prescribed burns to compare post-fire plant succession with site characteristics associated with nest sites. Nest sites had lower amounts of grass standing crop, grass ground cover, and higher amounts of woody vegetation than found in the 0.04-ha area immediately surrounding nests. Vegetation structure at nests sites was similar to the structure measured across the 20-ha area <6 months following burns, but vegetation structure at ground level began to deviate ≥6 months after fires such that ≥50% of the values differed from the values recorded at nest sites. Results point to the importance of open vegetation structure at ground level and the need for frequent burning to maintain appropriate nesting habitat. Vegetation characteristics associated with nest sites appear to be highly ephemeral and tightly linked to conditions at ground level. As such, suitable nest sites likely represent a subset of areas occupied by singing males.

Adaptation to ephemeral habitat may overcome natural barriers and severe habitat fragmentation in a fire-dependent species, the Bachman's Sparrow (Peucaea aestivalis).

Bachmans Sparrow (Peucaea aestivalis) is a fire-dependent species that has undergone range-wide population declines in recent decades. We examined genetic diversity in Bachmans Sparrows to determine whether natural barriers have led to distinct population units and to assess the effect of anthropogenic habitat loss and fragmentation. Genetic diversity was examined across the geographic range by genotyping 226 individuals at 18 microsatellite loci and sequencing 48 individuals at mitochondrial and nuclear genes. Multiple analyses consistently demonstrated little genetic structure and high levels of genetic variation, suggesting that populations are panmictic. Based on these genetic data, separate management units/subspecies designations or translocations to promote gene flow among fragmented populations do not appear to be necessary. Panmixia in Bachmans Sparrow may be a consequence of an historical range expansion and retraction. Alternatively, high vagility in Bachmans Sparrow may be an adaptation to the ephemeral, fire-mediated habitat that this species prefers. In recent times, high vagility also appears to have offset inbreeding and loss of genetic diversity in highly fragmented habitat.

Bachman's Sparrow (Peucaea aestivalis) response to variation in the extent of burns conducted during the nesting season

Bachmans Sparrow (Peucaea aestivalis), an endemic North American passerine, requires frequent (≤ 3 yr) prescribed fires to maintain preferred habitat conditions. Prescribed fires that coincide with the sparrows nesting season are increasingly used to manage sparrow habitat, but concerns exist regarding the effects that nesting-season fires may pose to this understory-dwelling species. Previous studies suggested that threats posed by fires might be lessened by reducing the extent of prescribed fires, thereby providing unburned areas close to the areas where fires eliminate ground-cover vegetation. To assess this hypothesis, we monitored color-marked male Bachmans Sparrows on 2 sites where the extent of nesting-season fires differed 5-fold (> 70 ha vs. 100,000 ha) using frequent prescribed fire (≤ 2-yr return intervals). Additional research is needed regarding the effects that nesting-season fires may have on small, isolated populations as well as sites where much larger burn extents (> 100 ha) or longer burn intervals (> 2 yr) are used.

Use of recorded vocalizations in winter surveys of Bachman's Sparrows

Abstract We used a recorded song of the Bachmans Sparrow (Aimophila aestivalis) to determine whether recorded vocalizations improved detection of this secretive species in winter. Surveys were conducted in the Red Hills region of northern Florida and southwestern Georgia under a range of climatic conditions. Bachmans Sparrows responded readily to taped vocalizations and were detected only on surveys where recorded vocalizations were used. A total of 251 individuals (mean = 1.01 per stop) was observed, or approximately 10–15 observations/h. Detections decreased at lower ambient temperatures and also varied among sites, but adequate numbers were observed even when maximum daytime temperatures remained < 3° C. We believe variation in the number of sparrows observed among sites may relate to variation in ground cover. Bachmans Sparrows were most common in areas with extensive native ground cover, but further studies are needed. We recommend use of recorded vocalizations in winter surveys of Bachmans Sparrows and suggest recorded vocalizations may help in winter surveys of other secretive sparrows.

Tool Usage by Juvenile Sitta pusilla (Brown-headed Nuthatch)

Abstract Although tool usage in adult birds is well documented, we have not found reports of juvenile birds using tools other than a few observations of individuals held in captivity. Here we describe the first observations of tool usage by juvenile birds in the wild. We observed juvenile Sitta pusilla (Brown-headed Nuthatch) using tools similar to those used by adults as early as 2 months post-fledging. We also observed juveniles attempting to use novel objects as tools, suggesting tool usage in this species may have both innate and learned components. Tool usage also takes place in 2 closely related nuthatch species and may be more common in this family of birds than currently known.

Uncommon Levels of Relatedness and Parentage in a Cooperatively Breeding Bird, the Brown-Headed Nuthatch (Sitta pusilla)

ABSTRACT Cooperatively breeding birds employ a variety of mating strategies, and we do not fully understand breeding group structure and the range of reproductive strategies used by group members. We examined group structure and parentage in a population of Brown-headed Nuthatches (Sitta pusilla). We genotyped 346 adults and nestlings banded at 59 nests using nine microsatellite loci to determine parentage and relatedness and compared the results to field observations of marked individuals from 282 nests monitored from 2006–2010. Based on field observations, 23% of nests were cooperative, and only 13% of the cooperative groups had more than one helper. Consistent with field observations, genetic analyses indicated that 83% of helpers were related to at least one parent at the nest, and that most helpers were male. Extra-group paternity appeared to be common at nests of both pairs (45%) and cooperative groups (32%, but did not differ in frequency between the two nest types. Although male helpers unrelated to the breeding female might be expected to sire offspring in cooperative groups, we did not observe this phenomenon. Instead, we found one, and possibly two, cases of incestuous breeding involving related helpers.

How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch

Breeder investment in offspring reflects a trade-off between the benefits realized from current reproductive efforts and the benefits expected from future reproductive opportunities. When assisted by nonbreeding helpers that provide care for offspring, breeders may modify reproductive investments to minimize the costs of producing offspring, or in ways that maximize productivity and offspring survival. How helpers assist breeders can vary with different stages of reproduction, and how breeders alter investment in response to helpers may change depending on the stage of reproduction. We assessed how helpers contribute to reproduction and how breeders alter their investment in response to helper contributions in the cooperatively breeding brown-headed nuthatch (Sitta pusilla). We assessed helper contributions across three stages of reproduction: (1) nest excavation, (2) maternal egg production, and (3) nestling care and development at days 8–12 post-hatching, a period of rapid nestling growth. We also investigated how breeders responded to helper contributions and the relationship of helper behavior with breeders’ reproductive success. Helpers contributed to offspring care but not nest excavation. Breeders assisted by helpers did not alter investments in nest excavation, offspring production, or offspring care. As a result, offspring raised by cooperative groups received more food and weighed more. Nests with helpers were more likely to fledge at least one offspring, even when considering variation in territory characteristics and breeder experience. Results indicate breeders likely benefit from the favorable breeding conditions helpers provided for current breeding efforts, which influenced the quality of offspring produced and their likelihood of fledging in this study.Significance statementHelpers may contribute to breeders’ reproductive effort during many stages of reproduction. The presence of nonbreeding helpers should therefore influence the investments made by breeders during different stages of breeding. Investment decisions in one stage should furthermore influence later investment decisions. We demonstrated that helpers assisted breeders primarily during the offspring rearing stage in brown-headed nuthatches (Sitta pusilla), a facultative cooperative breeder. Breeders with helpers maintained their level of investments in offspring similar to the investments documented for breeders without helpers. As a result, chicks in nests with helpers received more food and were heavier, and adults with helpers were more likely to fledge at least one young. Our results suggest that the combined effects of parental and helper investment provided benefits for current broods with potentially important survival consequences for offspring.

An Unusual Song-Like Vocalization Produced by Female Bachman's Sparrows (Peucaea aestivalis)

Abstract We describe a new female vocalization for Peucaea aestivalis (Bachmans Sparrow) that may represent a type of female song. The vocalization has characteristics that are similar to the “excited” or “flight” songs that male P. aestivalis produce, and similar song characteristics can be found among other members of the genus, including one congener for which female singing is common. Two marked female P. aestivalis were observed producing the vocalization as well as four unmarked individuals that were paired with territorial males. A recording of one of these unmarked individuals collected in 1989 is similar to the vocalizations observed for marked females. Field notes collected at the time the recording was made suggested the “odd song” was produced by a female, and we provide a sonogram of this new vocalization based on this recording. The vocalization appears to be rare and may be difficult to link to external stimuli and social function.