Acorn Woodpecker Research Articles

Interspecific Cooperative Nesting between Barn Swallows and Say's Phoebes in South-Central New Mexico

Intraspecific cooperative nesting is not a common event in the avian world, although it is well documented in species like the Acorn Woodpecker (Melanerpes formicivorus; Koenig et al. 1984) and Common Moorhen (Gallinula chloropus; Gibbons 1986). Intraspecific cooperative nesting occurs when more than two birds of the same species take part in providing parental care to rear the young (Emlen and Vehrencamp 1983). Our purpose is to document an observation of interspecific cooperative nesting between a pair of Barn Swallows (Hirundo rustica) and a Say's Phoebe (Sayornis saya). We have found no published records that document interspecific cooperative nesting in birds. This event is even more unusual in that Say's Phoebes often usurp Barn Swallow nests (Bent 1942). In late March 1993, a pair of Say's Phoebes built a nest atop an old Barn Swallow nest at our housing facilities at the Orogrande base camp on the Fort Bliss Military Reservation. The nest was located at the juncture of two steel girders supporting the roof. Orogrande is located in south-central New Mexico, approximately 96 km north of El Paso, Texas. Adjacent habitat is Chihuahuan Desert scrub (Shreve 1942) and desert grassland (Budd et al. 1979). After fledging one of three young in late April, the phoebes left the general area and were observed occasionally foraging from surrounding poles and utility wires. A short time after the phoebe fledged, Barn Swallows began to occupy and restore other nearby swallow nests with no apparent interest in the phoebe nest. On 13 June, we observed Barn Swallows lining the phoebe nest with feathers. Barn Swallows commonly line their nests with feathers, but phoebes do not (Terres 1991). On 15 June, we discovered a Barn Swallow egg in the phoebe nest. Because nest reuse occasionally occurs in birds (Butler 1980, Butler and Campbell 1987, Shields et al. 1988), the fact that the Barn Swallows were using the phoebe nest did not appear odd. However, later that same day, a Say's Phoebe was observed on the nest. We checked the nest using a mirror and saw that a Barn Swallow egg

Patterns and consequences of egg destruction among joint-nesting acorn woodpeckers

Reproductive competition among joint-nesting female acorn woodpeckers, Melanerpes formicivorus, culminates in the removal and subsequent destruction of eggs laid by co-breeders. Females destroying eggs gain both by synchronizing egg laying and by having more of their own eggs incubated in the final clutch. Here results are summarized based on observations of 19 joint nests. Egg destruction accounted for the loss of 38% of all eggs laid. Either or both joint-nesting females destroyed eggs at the same nest, and a female that destroyed eggs during one nesting attempt sometimes had her own eggs destroyed during the next. Egg destruction was not moderated by the genetic relatedness of joint-nesting females and was apparently unrelated to behavioural dominance, but substantially lowered per female success of three- compared with two-female nests. Females did not discriminate between eggs; thus egg destruction ended when both females laid normal eggs simultaneously in the nest cavity. However, egg destruction ended most frequently when a female did not destroy an egg laid by her co-breeder 1 day prior to laying her own first egg. Such failures to destroy eggs entail short-term fitness costs that may be compensated by the potential for reciprocity across breeding attempts. Abnormally small ‘runt’ eggs, rarely found in other species of birds, were commonly laid as the first egg of the clutches of one or both joint-nesting females. The laying of runt eggs may allow females to destroy normal eggs laid simultaneously by their co-breeders. Egg destruction is a major constraint on the degree to which females nest jointly. More generally, egg destruction and its associated behaviour patterns demonstrate that reproductive interference can be as complex and destructive within groups of close relatives as between unrelated individuals.

Energetic Benefits of Communal Roosting by Acorn Woodpeckers during the Nonbreeding Season

We examined the thermal consequences, energy benefits and patterns of nighttime communal roosting in Acorn Woodpeckers (Melanerpesformicivorus) during the nonbreeding season, the period when they are most reliant on nutrient-poor acorn stores. Because the oak limbs (Quercus) in which Acorn Woodpeckers excavate roost cavities cool more slowly than the surrounding air, the nighttime temperature inside unoccupied woodpecker roost cavities averaged 4.3*C higher than the outside ambient temperature, when the latter was approximately 0*C. The temperature of occupied roosts was further augmented in proportion to the number of birds sharing the roost. A single woodpecker increased the cavity temperature an additional 1.20C, whereas four birds increased it an additional 6.0*C. Acorn Woodpeckers did not huddle together at low air temperatures when placed in a simulated roost-cavity metabolism chamber. Consequently their nighttime, fasted oxygen consumption was independent of group size (one, two, or four birds) and was described by the relation: ml O0/(g hr) = 3.33-0.055 Ta. From this relation and our cavity temperature measurements, we estimate that at an outside temperature of 0?C a single cavity-roosting woodpecker would reduce its heat loss by at least 9%, whereas four birds would reduce their heat loss by at least 17%, and even more in the presence of wind. This energy savings may contribute to the higher winter survival noted for male Acorn Woodpeckers that live in larger groups.

Dominance within broods of the cooperatively breeding acorn woodpecker

Abstract. The study of dominance among juvenile broodmates controls for factors such as age and experience that are known to influence dominance. In acorn woodpeckers, Melanerpes formicivorus, broodmates remain together on the natal territory for at least 1 year and potentially compete for various resources. Moreover, many broodmates remain together for their entire lives and share mates as members of polygynous or polyandrous groups. Dominance interactions were observed between acorn woodpecker broodmates following fledging. Although dominance interactions occurred both within and between sexes, neither sex was over- or under-represented among dominants. Dominance appeared to have no effect on post-fledging mortality. Relative wing length prior to fledging was the best predictor of dominance, followed by relative body mass prior to fledging. Relative bill length showed the poorest association with dominance. The highly significant association between dominance and relative wing length at the time of banding appears to be due to the strong relationship between hatch order and subsequent wing length rank prior to fledging.

Geographic Variation in Coloration and Morphology of the Acorn Woodpecker

Although geographic variation in coloration and morphology of Acorn Woodpeckers (Melanerpes formicivorus) is thought to be slight, a sedentary species restricted to a particular habitat across a broad geographic range may be expected to exhibit some geographic differentiation. I analyzed seven morphometric and five plumage coloration characters on 1,531 study skins from across the species' geographic range. Dividing the specimens examined into 25 population samples, I found highly significant geographic differences in most of the characters analyzed, including clinal patterns and discrete differences in both morphometric and plumage characters. Patterns of geographic differentiation in the two character sets were not significantly concordant. It is possible to identify seven geographic units within the species, each of which is diagnosable based on combinations of discrete and continuous character states. Resumen. A pesar de que se ha pensado que la variación geográfica en el Carpintero Arlequín (Melanerpes formicivorus) es mínima, se puede esperar que una especie sedentaria y restringida a un hábitat particular que se distribuye sobre un área de distribución muy amplia, mostrará diferenciación en alguna escala geográfica. En este trabajo, se analizaron siete caracteres morfométricos y cinco de coloración del plumaje en 1,531 especímenes de toda el área geográfica de la especie. Se encontró variación geográfica significativa en la mayoría de los caracteres analizados, incluyendo patrones clinales y diferencias discretas entre poblaciones. Basándose en estos patrones, es posible identificar siete unidades geográficas en la especie, cada una diagnosticable con estados de caracteres discretos.

Environmental Variation and the Persistence of Small Populations

Understanding the factors that determine the continued survival of small populations is a central problem in conservation biology. The Acorn Woodpecker (Melanerpes formicivorus) naturally occurs in small, isolated populations throughout much of the American Southwest. In spite of this distributional pattern, the species is neither rare nor endangered. Thus it appears to have successfully "solved" the problems to the problems of habitat fragmentation. We used data from a 10-yr field study and simulation models to examine the effects of environmental stochasticity on population survival times. All simulated woodpecker populations went extinct within 49 yr, and the median survival time was only 16 yr. However, when immigration was allowed, persistence times greatly increased; with an immigrant rate of only five individuals per year, most populations lasted >1000 yr. The results of this and other analyses suggest that this population persists only because it is part of a larger "metapopulation," and because it is regularly rescued from extinction by immigration from other, independently varying, populations. This finding has important implications for the development of management strategies designed to preserve small populations that are faced with fragmented distributional patterns and high levels of environmental variation.

Distress Calls in the Acorn Woodpecker

Acorn Woodpeckers live in extremely stable kin groups. Nonetheless, only 59.9% of birds caught in roosting aggregations gave distress calls or fear screams. Distress was highly repeatable among individuals and apparently heritable. However, the incidence of distress did not vary seasonally or according to age, sex, or status. Also, with two marginally significant exceptions, distress calls did not vary consistently with group characteristics or with the composition of roosting aggregations. Screams did not attract conspecifics, but sometimes attracted large mammalian predators. These results fail to support Rohwer's (1975) calling for help hypothesis and instead are consistent with Higstedt's (1983) predator attraction hypothesis that distress calls function to attract secondary predators that will distract or dispute the original predator, thereby inadvertently allowing the caller to escape.

The Effects of Tannins and Lipids on Digestion of Acorns by Acorn Woodpeckers

-The effects of tannins and lipids on the metabolizable energy coefficient (MEC; i.e. energy ingested minus energy excreted, divided by energy ingested) of Acorn Woodpeckers (Melanerpes formicivorus) fed acorn meal of known composition was determined by feeding trials on captive birds. Adding tannins decreased MEC, while adding acorn lipid increased it. Quebracho (a condensed tannin) had a stronger detrimental effect on MEC than did tannic acid (a hydrolyzable tannin). There was a significant interaction (associative digestion) between tannic acid and lipid, such that the detrimental effects of tannic acid were enhanced in the presence of increased lipid. Despite the detrimental effects of added tannin, MEC of acorns, which are naturally high in tannins, was similar to the MEC of crickets, which are low in tannins. The amount of energy Acorn Woodpeckers derived from acorns (net energy value) averaged 69.0% of their maximum estimated energetic content based on composition and 60.5% of their total gross energy based on bomb calorimetry. The study indicates that stored acorns are more important to Acorn Woodpeckers than previously estimated. On average, however, acorns supply only a small proportion of the energetic needs of this species during the winter in central coastal California. Received 16 January 1990, accepted

Breeding Energetics and Thermal Ecology of the Acorn Woodpecker in Central Coastal California

We used the doubly labeled water (DLW) technique to measure the field metabolic rate (FMR) of adult (n = 4) and nestling (n = 30) Acorn Woodpeckers (Melanerpes formicivorus). Resting metabolic rate (RMR) of adults and nestlings was calculated from 02 consumption. We constructed the nestlings' energy budget from measurements of the growth rate, FMR, and RMR of different aged nestlings. We measured the body temperature (Tb) of two nestlings in the field using implanted radiotelemeters, assessed the nestlings' thermal environment in terms of the air temperature (Tj experienced inside and outside of nest cavities, and studied the ontogeny of nestling homeothermy in the laboratory. Adult FMR averaged 195 kJ/day, which is 30% lower than predicted from adult mass (82 g) and 2.7 times the measured basal metabolic rate. Nestling FMR (kJ/day) increased with mass (m in grams) according to the relation: FMR = -27.1 + 2.4m. Nestling FMR stabilized at about 160 kJ/day (82% of the adult level) by 3 weeks of age. Nestlings, which are adult sized when they fledge 30-32 days after hatching, grow relatively slowly. Their logistic growth rate constant (K = 0.226) is 30% lower than predicted from their mass and is equivalent to that of a tropical species of their size. Nestlings also develop endothermy much more slowly than expected and are unable to maintain adult Tb when exposed to 150C for 30 min until they are 3 weeks old. In the field, nestling Tb fluctuated until about 3 weeks of age, apparently due to intermittent brooding by the adults. Nestlings metabolized an average of 3,853 kJ/bird over the nestling period (age: 0-31 days). Of the total, RMR comprised 46.8%, whereas activity, thermoregulation, and the heat increment of feeding combined accounted for 40.2%. The energy accumulated in growth amounted to 501 kJ, or 13% of the total. Gross growth efficiency (ratio of energy accumulated in tissue to total metabolized energy) is the lowest reported for any bird. Two factors contribute to low growth efficiency: (1) a slow growth rate, which may result in part from tannins contained in the nestling's partially acorn diet, and (2) thermostatic costs associated with a low nest-cavity Ta. These unusual physiological features indicate that energetic constraints may play an important role in influencing the costs and benefits of group living in this cooperatively breeding species.

Individual Contributions to Cooperative Nest Care in the Acorn Woodpecker

Etude du role du statut reproducteur, du sexe, de l'age et de la taille du groupe sur la contribution individuelle a l'incubation, la couvaison, le nourrissage et le nettoyage du nid

Competition between European Starlings and Native Woodpeckers for Nest Cavities in Saguaros

-European Starlings (Sturnus vulgaris) have recently invaded Arizona and breed in some areas but not in similar areas nearby. In Arizona, European Starlings commonly nest in cavities in saguaro cacti (Carnegiea gigantea) but do not excavate these cavities. To examine whether European Starlings compete with native woodpeckers for nest cavities in saguaros, we studied Gila Woodpeckers (Melanerpes uropygialis) and Northern Flickers (Colaptes auratus) in areas with European Starlings and in similar, nearby areas with no European Starlings. We determined which factors explained the variation in the number of nests of each species present on fifteen 10-ha plots. We also compared the location and dimensions of nest cavities used by each species to determine whether European Starlings use Gila Woodpecker nest cavities, Northern Flicker nest cavities, or both. We found that European Starlings compete with Gila Woodpeckers but not with Northern Flickers. This competition decreases the number of Gila Woodpeckers that nest in areas where European Starlings nest. European Starlings used Gila Woodpecker nest cavities, and there was a negative relationship between the number of European Starling nests and the number of Gila woodpecker nests that explained 46.7% of the variation in the number of Gila Woodpecker nests on the plots. European Starlings did not use Northern Flicker nest cavities, and we found no relationship between the number of European Starling nests and the number of Northern Flicker nests. In addition, the number of Gila Woodpecker nests was positively related to the number of large saguaros and negatively related to the slope of the plot. The number of Northern Flicker nests was positively related to the volume of ironwood (Olneya tesota). The number of European Starling nests was negatively related to the distance to agriculture and large lawns. Received 29 June 1989, accepted 4 December 1989. EUROPEAN Starlings (Sturnus vulgaris) were introduced into North America in 1890 and rapidly spread throughout most of the United States (Kessel 1953). They were not observed in Arizona until ca. 1946 (Monson 1948). In Arizona, European Starlings commonly nest in cavities in saguaro cacti (Carnegiea gigantea), but they do not excavate these cavities (Kessel 1957). Gila Woodpeckers (Melanerpes uropygialis) and Northern Flickers (Colaptes auratus) excavate these cavities in saguaros for nest sites (Gilman 1915, Bent 1939), and the nesting season of the European Starling overlaps that of the Gila Woodpecker and the Northern Flicker (Gilman 1915, Bent 1939, Royall 1966). Brenowitz (1978) observed European Starlings usurp nest cavities from three pairs of Gila I Present address: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 USA. Woodpeckers. One pair of Gila Woodpeckers lost three successive cavities to European Starlings. European Starlings have been observed usurping nest cavities from Northern Flickers in New Hampshire (Shelly 1935), Maryland (Howell 1943), and Massachusetts (Bent 1950). European Starlings have also usurped nest cavities from many other species including Purple Martins (Progne subis) in Michigan (Allen and Nice 1952), Red-bellied Woodpeckers (Melanerpes carolinus; Kilham 1958) and Wood Ducks (Aix sponsa; McGilvrey and Uhler 1971) in Maryland, Acorn Woodpeckers (Melanerpes formicivorus) in California (Troetschler 1976), Eurasian Nuthatches (Sitta europaea) in Sweden (Nilsson 1984), and Buffleheads (Bucephala albeola) in British Columbia (Peterson and Gauthier 1985). Van Balen et al. (1982) concluded that by competing for nest cavities European Starlings decreased the number of Great Tits (Parus major) nesting in their study area in the Netherlands. Our objective was to determine whether Eu367 The Auk 107: 367-375. April 1990 This content downloaded from 157.55.39.78 on Sun, 19 Jun 2016 05:49:35 UTC All use subject to http://about.jstor.org/terms 368 KERPEz AND SMITH [Auk, Vol. 107 ropean Starlings competed with Gila Woodpeckers and Northern Flickers for next cavities in saguaro cacti, and if so, to evaluate the effects of this competition. European Starlings presently breed in some areas of Arizona but not in similar areas nearby. Therefore, we were able to study Gila Woodpeckers and Northern Flickers in areas with no European Starlings and in similar, nearby areas with various densities of European Starlings. To assess the effect of competition, we studied the relationship between the number of European Starlings nesting in an area and the number of Gila Woodpeckers and Northern Flickers nesting in that area. We examined the relationships between habitat variables and the numbers of nesting Gila Woodpeckers, Northern Flickers, and European Starlings to separate the effects of habitat and competition. We also compared the location and dimensions of nest cavities used by each species to determine whether European Starlings use Gila Woodpecker nest cavities, Northern Flicker nest cavities, or both.

Observations on Food Habits and Social Organization of Acorn Woodpeckers in Costa Rica

Observations sur la taille des groupes,le comportement d'approvisionnement et l'utilisation des glands de Quercus costaricensis par une population du Costa Rica

Population Ecology of the Cooperatively Breeding Acorn Woodpecker

Ever since the acorn woodpecker was observed and described by Spanish explorers, its behavior--particularly the unique habit of caching acorns in specialized storage trees or granaries--has impressed observers. Acorn woodpeckers are also one of the few temperate zone species in which young are reared communally in family groups. This demographic study investigates the complexities of acorn storage and group living in acorn woodpeckers at Hastings Reservation in central coastal California. It is one of the most thorough studies of any avian social system to date.

The Implications of Germinating Acorns in the Granaries of Acorn Woodpeckers in Panama

Influence de la germination des glands dans les caches de Melanerpes formicivorus sur le comportement d'amassement et la taille des groupes au Panama

Nesting Phenology and Competition for Nest Sites among Red-Headed and Red-Bellied Woodpeckers and European Starlings

Nesting Phenology and Competition for Nest Sites among Red-Headed and Red-Bellied Woodpeckers and European Starlings

Population Ecology of the Cooperatively Breeding Acorn Woodpecker, by Walter D. Koenig and Ronald L. Mumme [Review

Population Ecology of the Cooperatively Breeding Acorn Woodpecker, by Walter D. Koenig and Ronald L. Mumme [Review

Joint nesting in the acorn woodpecker

Control of invasive sea lamprey in the Great Lakes with a selective pesticide (lampricide) that targeted larval sea lamprey began in the late 1950's and continues to be one of the main methods for control. Although the Great Lakes Fishery Commission, which was formed with the mandate of controlling sea lamprey, often expresses the success of the sea lamprey control program in terms of percent reduction from lake-wide pre-lampricide control adult sea lamprey abundances, there remains a large amount of uncertainty surrounding these estimates. In this study, we gathered historical data on adult sea lamprey captures from trapping efforts from the mid-1950's through the late 1970's to better understand pre-control abundance. We used this information to estimate lake-wide population abundances of adult sea lamprey using a weighted linear regression that includes environmental and lampricide treatment predictor variables. We varied trapping efficiency for early trapping data to evaluate the uncertainty in abundance estimates. Pre-control adult sea lamprey abundances in all lakes were much greater than current population sizes, but estimates were quite sensitive to trapping efficiency. In Lake Superior, declines in abundance aligned with increases in control efforts, but in other lakes, declines were occurring prior to the onset of lampricide application, perhaps because of a loss of prey. We suggest that previous estimates of pre-control adult sea lamprey abundance may have been underestimated unless trapping efficiency was greater than what is currently achieved in the basin.

Population Ecology of the Cooperatively Breeding Acorn Woodpecker

Population Ecology of the Cooperatively Breeding Acorn Woodpecker

Ability of Two Species of Oak Woodland Birds to Subsist on Acorns

Acorns are an extremely important food resource for bird populations in temperate North America (Martin et al. 1951). However, relatively little is known about the ability of animals to digest and maintain themselves on acorns. Nowhere is this ignorance more blatant than in California, where 15 species of oaks (Quercus spp.) dominate millions of hectares of land area (Griffin and Critchfield 1972, Griffin 1977), and serve (via their fruit) as a primary food resource for at least 16 species of birds (Martin et al. 1951). Of the birds dependent on acorns in foothill woodland regions of California, two of the most characteristic are the Acorn Woodpecker (Melanerpesformicivorus) and Scrub Jay (Aphelocoma coerulescens). The former is well known for its habit of caching large numbers of acorns in specially modified storage trees or granaries (MacRoberts and MacRoberts 1976). Acorns comprise over 50% of this woodpecker's total diet (Beal 1911), and are critical to overwinter survival and subsequent spring breeding (Koenig and Mumme 1987). Acorns also comprise over 50% of the fall and winter diet of Scrub Jays (Beal 1910; W. J. Carmen, unpubl. data). Despite the dependence of these species on acorns, it is unknown to what extent, if any, they are able to circumvent the effects of tannins, a key secondary metabolite present in acorns. Tannins bind with proteins (Martin and Martin 1982) and are generally accepted as defense compounds against herbivory (Bate-Smith 1973, Tempel 1981). This study was conducted in order to obtain preliminary data on the ability of Acorn Woodpeckers and Scrub Jays to overcome tannins and to maintain their body mass exclusively on acorns.

Costs and Benefits of Joint Nesting in the Acorn Woodpecker

The acorn woodpecker (Melanerpes formicivorus) is a cooperative breeder that lives in permanently territorial family groups of 2-15 individuals. Although most groups contain only one breeding female, 22% contain two jointly nesting females, which both lay eggs in the same nest and cooperatively rear the young of that nest. Both joint and solitary nesting coexist within the same California population, even though females that nest jointly destroy each other's eggs and have significantly lower annual reproductive success than females that nest singly. Here we examine the relative costs and benefits of joint nesting, primarily by means of a demographic model. Our analysis indicates that a number of ecological and social factors have influenced the relative advantages and disadvantages of joint nesting and that the fitness of females that nest jointly appears to be comparable to (or only slightly lower than) that of females that breed singly. Factors reducing the short-term reproductive costs of joint nesting...