Influence of reduced food availability on growth of captive American kestrels

Abstract

Captive American kestrels (Falco sparverius) were used to model the effect of low prey availability on growth and survivorship potential in nestling raptors. The experimental design consisted of 4 treatments: nestlings were fed ad libitum (100% diet) or on increasingly restricted diets (90, 80, and 70% of the ad libitum diet). Nestlings fed a reduced diet grew significantly more slowly than those fed the ad libitum diet, as shown by the body mass growth constant. The restricted diet had no significant effect on the asymptotic size of the kestrels, i.e., body mass and tarsus and antebrachium lengths. However, young kestrels fed reduced diets (80 and 70%) had a lower body mass at fledging than those fed ad libitum and the 90% diet, although they fledged at the same age. The growth of the ninth primary was slower for birds on restricted diets than for those fed ad libitum. Sexual dimorphism was observed for body mass and antebrachium growth constants, with males growing faster than females. However, females reached a higher asymptotic body mass and antebrachium length, as well as a higher body mass at fledging, than males. Thus, when prey availability is reduced by as much as 30%, nestling kestrels grow more slowly and store less fat, which could lead to poorer postfledging survivability.

Growth and development of house sparrows (Passer domesticus) in response to chronic food restriction throughout the nestling period

“…In both our control and food-restricted house sparrows, we observed rapid increases in tarsus length during the first week post-hatch, followed by slowed growth to day 12. Growth of the tarsus, skull and wing of food-restricted house sparrows was maintained in line with that of adequately fed controls, which is in agreement with previous studies showing prioritization of skeletal growth (relative to mass gain) in altricial young faced with acute or chronic, moderate restriction (Negro et al, 1994;Lacombe et al, 1994;Lepczyk and Karasov, 2000;Moe et al, 2004). An equivalent prioritization of skeletal growth was observed in our preliminary study of 25% chronic restriction lasting until 25days post-hatch in house sparrows (Killpack et al, 2010).…”

“…However, food-restricted birds maintained skeletal growth in line with controls and fledged at the same age (Killpack et al, 2010). This pattern of reduced asymptotic body mass and maintenance of skeletal growth and fledging date has also been demonstrated with chronic 20-30% food restriction in captive American kestrels (Lacombe et al, 1994). Thus, maintenance of skeletal growth within the limitations imposed by chronic, moderate food restriction may allow birds to avoid the enduring negative consequences of reduced structural size on competitive abilities and survival within and outside of the nest.…”

Impacts of Short-Term Food Restriction on Immune Development in Altricial House Sparrow Nestlings

“…Our findings of reduced body mass, organ mass, and structural size in food-restricted nestlings support the previously demonstrated resource dependence of growth and maintenance in young birds (Lacombe et al 1994;Negro et al 1994;Burness et al 2000;Brzęk and Konarzewski 2001;Dahdul and Horn 2003;Moe et al 2004;Killpack and Karasov 2012a). Body mass, Food Restriction and Immune Development in Nestlings 203 organ mass, and structural size were recovered in refed birds, indicating flexibility to immediate resource supply.…”

“…Growth rates of altricial nestlings can be flexible to resource supply, and in some cases nestlings have been shown to slow growth during periods of food restriction and later "catch up" following return to adequate resources (Lepczyk and Karasov 2000;Bize et al 2006;Hegyi and Török 2007;Criscuolo et al 2008Criscuolo et al , 2011Killpack et al 2014). It is well documented that allocation patterns to organ growth and maintenance metabolism are altered during food restriction in nestlings (Lacombe et al 1994;Negro et al 1994;Burness et al 2000;Brzęk and Konarzewski 2001;Dahdul and Horn 2003;Moe et al 2004;Killpack and Karasov 2012a). Recent studies have shown that components of both the innate (e.g., antimicrobial proteins, natural antibodies, complement) and adaptive (e.g., B-and Tlymphocyte activities) arms of the immune system rapidly increase throughout the nestling and postfledging period of altricial birds (Palacios et al 2009;Stambaugh et al 2011;Killpack and Karasov 2012b;Killpack et al 2013).…”

“…First, we included these measurements to have an independent assessment that our experimental feeding protocol imposed a state of restriction in the nestlings. Second, given that food restriction during the nestling period has been shown to result in declines in the mass of internal organs and muscles (Lacombe et al 1994;Negro et al 1994;Burness et al 2000;Brzęk and Konarzewski 2001;Dahdul and Horn 2003;Moe et al 2004;Killpack and Karasov 2012a), these variables provide a useful comparator system for examining the flexibility of nestling immune system development to resource limitation. Finally, inflammatory responses involve systemic physiological alterations in addition to the release of acute-phase proteins (reviewed in Sköld-Chiriac et al 2014;O'Reilly and Eckersall 2014), and therefore body mass and temperature measures may be used to examine those responses following LPS immune challenge.…”