Harrison B. Tordoff

The Influence of Daylength on Reproductive Timing in the Red Crossbill

Early studies of reproductive timing in birds led to generalizations overemphasizing the importance of daylength as a regulating factor. Daylength is certainly important in stimulating gonadal development in many insectivorous passerines of temperate latitudes, but other factors, such as rainfall or its consequences, appear to control time of breeding in some birds of desert and tropical regions (Keast and Marshall, 1954; Miller, 1959, 1961; Immelmann, 1963; Oksche et al., 1963). Moreover, the unpredictable occurrence of reproduction in the Red Crossbill (Loxia curvirostra) suggests the influence of nonphotoperiodic factors on this largely boreal species. The Red Crossbill probably has the most erratic breeding schedule of any North American bird. At various localities in its range, it has been found over a period of time breeding in every month of the year. The nomadic tendencies of this species make the situation even more unusual. A locality inhabited by breeding birds in one year may not be used for several years thereafter. These irregularities in timing and location of breeding suggest that reproduction in this species is not primarily dependent on daylength. The extent of this dependence is analyzed in this paper.

Observations on Metabolism of Sodium Chloride in the Red Crossbill

OVER the past five years the capacities of several land birds for obtaining osmotically unobligated water from saline solutions have been evaluated (see Bartholomew and Cade, 1963). Such studies have contributed to an understanding of the water economies of species inhabiting salt marshes (Cade and Bartholomew, 1959) and to some assessment of the potential of species inhabiting deserts for gaining water from saline sources (Bartholomew and Cade, 1958). Studies of utilization of saline solutions have recently been supplemented by analysis of kidney function in the House Finch (Carpodacus mexicanus) and certain subspecies of the Savannah Sparrow (Passerculus sandwichensis) by Poulson and Bartholomew (1962a, b). Despite significant advances in the understanding of electrolyte metabolism of wild land birds, many additional studies are needed. The high order of interspecific and even intraspecific variability in this area hinders generalizations concerning salt tolerances of these animals. Moreover, studies of electrolyte excretion should be extended beyond the two species on which data are now available. For these reasons we undertook this investigation of the Red Crossbill (Loxia curvirostra). We considered this bird of particular interest because of its habit of eating salt in the wild-most of our experimental birds were obtained with a trap baited with a block of salt. The observations reported here concern capacities of individuals of this species for utilizing sodium chloride solutions of various concentrations and their response to injected loads of this salt.